February 2004 • NREL/TP-500-35109 

Evaluation of RCAS Inflow 

Models for Wind Turbine 

Analysis 

J. Tangler 

G. Bir 

National Renewable Energy Laboratory 

1617 Cole Boulevard 

Golden, Colorado 80401-3393 

NREL is a U.S. Department of Energy Laboratory

Operated by Midwest Research Institute • Battelle 

Contract No. DE-AC36-99-GO10337 
February 2004 • NREL/TP-500-35109 

Evaluation of RCAS Inflow 

Models for Wind Turbine 

Analysis 

J. Tangler 

G. Bir 

Prepared under Task No. WER3 3110 

National Renewable Energy Laboratory 

1617 Cole Boulevard 

Golden, Colorado 80401-3393 

NREL is a U.S. Department of Energy Laboratory

Operated by Midwest Research Institute • Battelle 

Contract No. DE-AC36-99-GO10337 
NOTICE

This report was prepared as an account of work sponsored by an agency of the United States 

government. Neither the United States government nor any agency thereof, nor any of their employees, 

makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, 

completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents 

that its use would not infringe privately owned rights. Reference herein to any specific commercial 

product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily 

constitute or imply its endorsement, recommendation, or favoring by the United States government or any 

agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect 

those of the United States government or any agency thereof. 

Available electronically at http://www.osti.gov/bridge 

Available for a processing fee to U.S. Department of Energy 

and its contractors, in paper, from: 

U.S. Department of Energy 

Office of Scientific and Technical Information 

P.O. Box 62 

Oak Ridge, TN 37831-0062 

phone: 865.576.8401 

fax: 865.576.5728 

email: reports@adonis.osti.gov 

Available for sale to the public, in paper, from: 

U.S. Department of Commerce 

National Technical Information Service 

5285 Port Royal Road 

Springfield, VA 22161 

phone: 800.553.6847 

fax: 703.605.6900 

email: orders@ntis.fedworld.gov 

online ordering: http://www.ntis.gov/ordering.htm 

Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste 
Contents 

Figures................................................................................................................................ iv 

Tables ................................................................................................................................ iv 

Executive Summary.............................................................................................................v

Background..........................................................................................................................1 

Objective ..............................................................................................................................2 

Approach..............................................................................................................................2 

Aerodynamic Inflow Models ...............................................................................................2 

Blade Element Momentum Theory..........................................................................3 

Generalized Dynamic Wake Theory........................................................................3 

Prescribed Vortex Wake ..........................................................................................4 

Free Wake Theory....................................................................................................4 

Dynamic Stall Model ...............................................................................................4 

Turbine Description .............................................................................................................5 

Predicted Angle of Attack....................................................................................................6 

Steady State, Axis Symmetric Results.....................................................................6 

Quasi-Steady State, Yawed Flow Results................................................................8 

Conclusions........................................................................................................................12 

Recommendations..............................................................................................................12

Acknowledgments..............................................................................................................13

References..........................................................................................................................13 

Appendix: Sample Input Files ...........................................................................................14 

RCAS Airfoil Data Set (S809.C81).......................................................................14 

RCAS Input File ....................................................................................................17 

WT_Perf Input File................................................................................................26 

AeroDyn/YawDyn Input File ................................................................................28 

LSWT Input File ....................................................................................................33 

iii 
Figures

Figure 1. UAE rotor blade geometry.................................................................................5 

Figure 2. S809 Delft wind tunnel data ..............................................................................6 

Figure 3. Effect of Prandtl tip/hub loss and induced swirl in WT_Perf............................6 

Figure 4. Angle of attack comparison of WT_Perf, AeroDyn, and RCAS.......................7 

Figure 5. Angle of attack comparison with generalized dynamic wake [4]......................8 

Figure 6. Angle of attack comparison for several wind speeds.........................................8 

Figure 7. Yawed flow of 10° at a wind speed of 10 m/s ...................................................9 

Figure 8. Yawed flow of 30° at a wind speed of 10 m/s .................................................10 

Figure 9. RCAS dynamic stall for 30° yaw at a wind speed of 10 m/s...........................10 

Figure 10. AeroDyn dynamic stall for 30° yaw at a wind speed of 10 m/s ......................11 

Figure 11. RCAS/AeroDyn dynamic stall for 30° yaw at a wind speed of 10 m/s...........11 

Tables 

Table 1. Program and Inflow Models Used in This Study..................................................2 

Table 2. Summary of Baseline Turbine Design Properties.................................................5 

iv
Executive Summary 

The finite element structural modeling in the Rotorcraft Comprehensive Analysis System 

(RCAS) provides a state-of-the-art approach to aeroelastic analysis. This, coupled with its 

ability to model all turbine components, results in a methodology that can simulate 

complex system interactions characteristic of large wind. In addition, RCAS is uniquely 

capable of modeling advanced control algorithms and the resulting dynamic responses. 

The aerodynamic inflow models in RCAS have been formulated for helicopter analysis. 

These models needed to be evaluated for wind turbine analysis to determine whether they 

included features that accurately predict the inflow for steady state, quasi-steady state, 

and unsteady operating conditions of wind turbines. The aerodynamic inflow models 

include the generalized dynamic inflow model, the equilibrium-based blade element 

momentum (BEM) theory, a prescribed vortex wake, and a free vortex wake. The four 

inflow methods in RCAS are listed in order of increasing complexity and computational 

time. The inflow models in RCAS were evaluated by comparing their predicted angles of 

attack for steady and quasi steady operating conditions with other wind industry 

aerodynamic models such as WT_Perf (BEM), AeroDyn (BEM and generalized dynamic 

wake), and LSWT (lifting surface prescribed wake). 

Momentum theory or the generalized dynamic-wake theory should be selected for most 

applications because both are simple and have rapid computational times. For unsteady 

inflow conditions the generalized dynamic wake inflow model is preferred because of its 

noniterative time domain formulation. The use of momentum theory in RCAS will 

depend on successful implementation of the Prandtl tip/hub loss model, induced swirl 

effects, and the Glauert approximation. Both the prescribed and free vortex wake options 

require exponential increases in computational time and use a basic lifting line blade 

representation. In unsteady inflow conditions these inflow models are less compatible 

with dynamic perturbations because of their discretized blade and wake vortex models. 

The prescribed and free wake vortex models are better suited for steady-state, axissymmetric performance prediction. However, for the prescribed and free wake vortex 

models, a lifting surface blade representation is preferred over a lifting line. 

v 
Background 

The Rotorcraft Comprehensive Analysis System (RCAS) is a state-of-the-art 

computational analysis system for modeling rotorcraft [1–4]. It can model a complete 

range of rotorcraft configurations in hover, forward-flight, and maneuvering flight 

conditions. RCAS can perform a variety of engineering calculations, including vehicle 

performance, aerodynamics and rotor loads, vehicle vibration, flight-control analysis, 

aeroelastic stability, flight dynamics, and flight simulation. Analysis features in RCAS 

include trim, maneuver, and stability. 

Structural modeling in RCAS uses a finite element approach for the various rotorcraft 

components. A helicopter model can include a conventional or multi-rotor configuration 

along with the fuselage, engine/drivetrain model, and control system. This structural 

modeling provides the capability for accurate dynamic simulation that includes the 

interaction between all system components. The rotorcraft system structural modeling 

capability can be adapted to model wind turbine systems, which would include the rotor, 

generator/drivetrain, nacelle, tower, and control system. Because wind turbines are 

becoming larger and more dynamically active, a comprehensive system dynamic 

simulation is more critical. 

Aerodynamic modeling in RCAS includes all rotorcraft system components such as 

rotors, wings, and fuselage. Two-dimensional airloads are used for blade and wing 

segments, three-dimensional airloads for the fuselage, and disc inflow models for the 

rotor. The resulting induced velocities and airloads are modeled separately for each 

component and collected in an aerodynamic library. RCAS includes four aerodynamic 

models that have been tailored for helicopter analysis to calculate the rotor’s induced 

inflow. Aerodynamic inflow models include the generalized dynamic wake theory [5], 

blade element momentum (BEM), prescribed wake, and free wake. These inflow methods 

are listed in order of increasing computational time and complexity. The BeddoesLeishman dynamic stall model [6] can be used with all inflow models. The generalized 

dynamic wake theory or BEM should be selected for most applications because they are 

simple and have rapid computational times. Both the prescribed and free vortex wake 

options result in exponential increases in computational time and use the basic lifting line 

blade representation rather than a lifting surface. 

The focus of this study was the aerodynamic modeling of the rotor in RCAS and 

assessing the suitability of the inflow models for predicting wind turbine blade loads and 

performance. Evaluation of the RCAS inflow models consisted of comparing their angleof-attack predictions to similar inflow models used in-house and in the wind industry. 

These models include WT_Perf [7], AeroDyn [8,9] and LSWT (Lifting-Surface 

Prescribed-Wake code) [10]. Both WT_Perf and AeroDyn have a BEM inflow model to 

predict rotor performance. In addition, AeroDyn includes the generalized dynamic wake 

inflow model and the Beddoes-Leishman dynamic stall model. Both codes can be used to 

predict steady state axis-symmetric performance and quasi steady state, yawed rotor 

performance. RCAS and AeroDyn, with the generalized dynamic wake theory can be 

used for unsteady performance prediction. The LSWT performance prediction code uses 

a prescribed, expanding-wake, inflow model. The code uses a lifting surface blade 

1
representation for blade geometry optimization and can also be used to predict steadystate, axis-symmetric performance and quasi-steady-state, yawed rotor performance. The 

comparison in this report included exercising all the inflow options in RCAS relative to 

those in NREL’s in-house performance prediction codes WT_Perf, AeroDyn, and LSWT. 

This was done using the UAE (unsteady aerodynamic experiment) two bladed, rotor 

geometry [11] and S809 [12] airfoil characteristics. 

Objective 

The objective of this study was to evaluate the aerodynamic inflow options in RCAS. To 

accomplish this objective, predicted angle of attack distributions obtained from RCAS 

were compared with industry-accepted aerodynamic codes that included WT_Perf, 

AeroDyn, and LSWT. The project scope was limited to axis-symmetric and yawed-flow, 

steady state operation with no structural degrees of freedom. 

Approach 

The UAE Phase VI wind turbine was selected for this code comparison. The upwind 

configuration of this two-bladed, horizontal-axis turbine has been the subject of several 

past studies. Consequently, input data for this turbine were available and results from this 

study will provide a baseline for future comparisons with UAE test data from the NASA 

Ames 80-ft by 120-ft (24.5-m by 36.5-m) wind tunnel. This 10-m (33-ft) rotor has 

tapered, twisted blades that use the NREL S809 airfoil profile from blade root to blade 

tip. S809 2-D airfoil data, from the Delft low turbulence wind tunnel, was used for 

calculating angle of attack distributions in RCAS, WT_Perf, AeroDyn, and LSWT. 

Operating cases included steady state axis-symmetric operation and quasi-steady state 

yawed flow operation. 

Aerodynamic Inflow Models 

RCAS, WT_Perf, and AeroDyn all employ the BEM inflow option for modeling wind 

turbine aerodynamics (see Table 1). In addition, RCAS and AeroDyn include a dynamic 

inflow option that minimizes computational time. For stall and post-stall calculations the 

prescribed wake inflow approach in LSWT and RCAS have the potential to more 

accurately predict the angle of attack. The free wake option in RCAS provides further 

flexibility to accommodate more inflow conditions at the expense of excessive computer 

time. Detailed descriptions of the theories each code employs can be found in their user 

and theory manuals. 

Table 1: Program and Inflow Models Used in this Study 

RCAS 1.9.5a BEM, Dynamic Inflow, Prescribed Wake, Free Wake 

WT_Perf 2.2 BEM 

AeroDyn 12.50 BEM, Dynamic Inflow 

LSWT 1.2 Prescribed Wake 

2
Blade Element Momentum Theory 

Below stall, BEM theory predicts reasonable angle-of-attack distributions for steadystate, axis-symmetric inflow conditions. Under stalled airfoil conditions, normally at high 

wind speeds, BEM over predicts the angle-of-attack distribution [13]. The over prediction 

is largely the result of two simplifying assumptions inherent in BEM. The “uniform 

inflow around the annulus” assumption leads to an over prediction of the angle of attack 

with the onset of stalled rotor conditions. The “no interaction between annuluses” 

assumption does not recognize the strong induced effect of trailing vorticity on the angle 

of attack distribution and resulting load distribution. 

For helicopter analysis, RCAS uses an effective-radius tip-loss model with no hub loss 

model. Typically, an effective radius input of 0.98 is used for helicopters, which means 

the blade radius is reduced by 2%. For wind turbines, the shorter radius from this tip loss 

model results in a larger blade pitch angle to achieve the designated thrust and power. 

Because the effective radius tip loss model has little effect on the blade load distribution 

it is not appropriate for wind turbine calculations. The Prandtl tip and hub loss models 

favorably decrease the tip and root loading and should be implemented in RCAS for use 

with the BEM inflow option. 

RCAS was formulated primarily for helicopter forward flight calculations, in which the 

axial induction factor is important and the swirl induction factor is insignificant. 

However, for wind turbine calculations the induced swirl is significant and results in a 

lower angle of attack distribution toward the blade root region. The induced swirl should 

be implemented in RCAS to improve accuracy and to provide results comparable with 

other wind turbine codes that include the induced swirl. 

For wind turbines, the Glauert empirical approximation improves accuracy at low wind 

speeds, high tip speed ratios, and high axial induction factors. The Glauert empirical 

approximation (also known as the windmill brake state model) calculates higher power 

coefficients than the classical momentum method at non-optimum pitch angles toward 

feather. This empirical approximation should be included in RCAS. 

Generalized Dynamic Wake Theory 

The generalized dynamic wake model is based on incompressible, potential flow, and 

small disturbance theory. This inviscid, non-interative, three-dimensional unsteady 

induced-flow theory is based on the unsteady theory of Peters and He [4]. The time 

domain model uses acceleration potential with a skewed cylindrical wake. This method 

calculates only the dynamic inflow perpendicular to the rotor disc as a function of the 

disc loading and air mass dynamic force. Wake induced swirl in the rotor plane, which is 

not important to helicopter analysis, is not calculated. The method implicitly includes 

Theodorsen and Loewy induced inflow effects from the shed wake as well as PrandtlGoldstein tip losses caused by the trailing wake. This inflow method is useful in 

analyzing skewed wake effects when operating off the wind axis. For helicopters, the 

method provides good correlation of the inflow relative to measurements, except near the 

blade tip. For yawed-flow calculations the method approximates the time lag between the 

initiation of a load disturbance and when it is felt at some other point in the flow field. Of 

3
all the inflow models it is best suited for aeroelasticity analysis, aeroelasticity tailoring, 

and higher harmonic control. It can also be applied to investigate coupled blade flap, 

lead-lag, and torsional stability. 

Prescribed Vortex Wake Theory 

Simplifying assumptions associated with blade element momentum and the generalized 

dynamic wake theories are largely eliminated through the use of a prescribed vortex 

wake. The method is better suited for axis-symmetric, blade geometry and performance 

optimization than either BEM or generalized dynamic wake theory, since it includes 

wake distortion and wake rollup. However, vortex wake inflow methods lend themselves 

to steady and quasi-steady analysis but are not well suited for unsteady aeroelasticity 

analysis. This drawback relates to the discretization of both the blade and wake vortex 

model, which tends to be less compatible with dynamic perturbations. The wake inflow 

model would likely need five inflow points per half cycle for the highest frequency of 

interest. Such a fine inflow resolution would lead to excessive computer time and 

frequent numerical instabilities. The RCAS prescribed wake model is based on helicopter 

contracting, prescribed wake equations that are limited to a constant diameter wake equal 

to the rotor diameter. Expanding wake prescribed equations, similar to those used in 

LSWT, are needed for this option to be viable for wind turbine analysis. In addition, the 

RCAS prescribed wake is used with a lifting line blade representation, whereas the 

expanding prescribed wake equations in LSWT are used with a lifting surface blade 

representation that includes induced effects for as many as five chordwise panels. 

Lacking the correct wind turbine prescribed wake equations, the RCAS prescribed wake 

model resulted in excessively high angle of attack predictions. 

Free Wake Theory 

A free wake inflow model is unencumbered by the use of prescribed wake equations and 

can accommodate a broader range of operating conditions. Several free wake 

formulations differ primarily in their numerical methods. The Leishman and Bhagwat 

free-vortex wake is the newest free wake option to be used in RCAS. For this wake 

model, the tip region trailing vorticity is truncated into a discrete tip vortex 15°–45° 

behind the blade. The free wake extends one and a half radii below the blade. The bottom 

of free wake is stabilized by evolutions of prescribed wake resulting from previous free 

wake iterations. Like the prescribed wake, the free wake is not well suited for unsteady 

aeroelasticity analysis because of wake discretization. Attempts to run the free wake for 

the UAE wind turbine rotor were not successful. The input data set included a large 

number of wake geometry input parameters that will require some trial and error to find a 

suitable combination. 

Dynamic Stall Model 

Dynamic stall behavior is characterized using the Beddoes-Leishman dynamic stall 

model with any of the RCAS inflow models. AeroDyn also uses the same dynamic stall 

model. The dynamic stall model is most compatible with the time domain based, 

generalized dynamic wake inflow model in RCAS and AeroDyn. In RCAS, the dynamic 

stall model is airfoil dependent and numerous airfoil specific input based to 2-D unsteady 

tests are required. Airfoil specific inputs in RCAS are defined only for the symmetric 

NACA 0012 airfoil and the SC1095 cambered airfoil. Only the cambered airfoil should 

4
be used in wind turbine analysis. In AeroDyn no airfoil inputs are required since the 

dynamic stall model is hard wired for a generic cambered airfoil. 

Turbine Description 

The UAE turbine geometry and aerodynamic information were obtained for the Phase VI 

UAE Rotor [10]. A summary of the turbine design properties for this two-bladed, 

upwind, horizontal-axis wind turbine appears in Table 2. 

Table 2: Summary of Baseline Turbine Design Properties 

Rotor Diameter 10.06 m 

Hub Height 12.2 m 

Rotor Precone 0° 

Shaft Tilt 0° 

Rotor Speed 72 rpm 

Tip Speed Ratio for Maximum Power Coefficient 7.0 

The UAE rotor blade geometry is shown in Figure 1. The blade uses the S809 airfoil 

from root to tip. Performance characteristics for the S809 airfoil, acquired in the Delft 

wind tunnel, are shown in Figure 2. For simplicity, the lift and drag data for a Reynolds 

number of 1,000,000 were used from blade root to tip in WT_Perf, AeroDyn, LSWT, and 

RCAS. 

The airfoil data input format for RCAS is derived from a Bell Helicopter’s dynamics 

code, “C81”, which was tailored for helicopter analysis. Each angle of attack in the data 

table is listed for multiple Mach numbers. For each Mach number, lift, drag, and moment 

coefficient are given. For wind turbines, compressibility effects are negligible and the 

airfoil characteristics can be held constant with Mach number. An example of a wind 

turbine airfoil input data set (S809.C81) with the S809 airfoil is shown in the Appendix. 

A simpler format is desired for wind turbine analysis. 

Figure 1. UAE rotor blade geometry. 

5 
Lift and Drag Coefficients 

Angle of Attack, deg. 

-0.2 

0.0 

0.2 

0.4 

0.6 

0.8 

1.0 

1.2 

-5 0 5 10 15 20 25 

lift coefficient 

drag coefficient 

Angle of Attack, degrees 

Figure 2. S809 Delft wind tunnel data. 

Predicted Angle of Attack 

Steady State Axis Symmetric Results 

The BEM inflow option in RCAS neglects several options—induced swirl, the Prandtl tip 

loss option, and the Glauert approximation—important to wind turbine analysis. NREL’s 

in-house BEM code, WT_Perf was used to illustrate the influence of the induced swirl 

and Prandtl tip loss option on the predicted angle of attack. Figure 3 shows the predicted 

angle of attack for the UAE two-bladed rotor at 7 m/s when no stall is present along the 

blade. Induced swirl, which adds to the local rotational speed, is greatest over the inboard 

portion of the blade and decreases with radius. Consequently, the inclusion of swirl 

decreases the angle of attack inboard by about 1° with almost no effect toward the tip. 

The Prandtl tip loss reduced the angle of attack by about 2° toward the tip. The Prandtl 

hub loss results in a fraction of a degree reduction toward the blade root. The Glauert 

approximation has little influence on the angle of attack distribution for optimum blade 

pitch. 

12.0 

10.0 

8.0 

6.0 

4.0 

2.0 

0.0 

WTPerf, 7 m/s 

WTPerf, 7 m/s, no tip/hub loss 

WTPerf, 7 m/s, no swirl, tip/hub loss 

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 

r/R 

Figure 3. Effect of Prandtl tip/hub loss and induced swirl in WT_Perf. 

6
20.0 

15.0 

WTPerf, BEM 

AeroDyn, BEM 

RCAS, BEM, tip loss=1.0 10 m/s 

7 m/s Angle of Attack, deg. 10.0 

5.0 

0.0 

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 r/R 

Figure 4. Angle of attack comparison of WT_Perf, AeroDyn, and RCAS. 

The BEM inflow option was used to show a comparison of the predicted angle of attack 

for WT_Perf, AeroDyn, and RCAS for wind speeds of 7 and 10 m/s (Figure 4). Close 

agreement is seen for WT_Perf and AeroDyn, both of which include the induced swirl, 

Prandtl tip loss, and Glauert approximation. WT_Perf also includes the Prandtl hub loss 

that is omitted in this version of AeroDyn. The higher blade root angle of attack is 

attributed to this omission. For both wind speeds, RCAS predicts noticeably higher angle 

of attack distributions by not including these inflow options. 

The dynamic wake inflow option [4] in RCAS provided better agreement with WT_Perf 

and LSWT over the outboard part of the blade (see Figure 5). For comparison, the RCAS 

BEM inflow option, with the over-predicted angle of attack is also shown. Both the BEM 

method WT_Perf and the prescribed wake method LSWT are in close agreement at 7 

m/s, except for the root region where LSWT has a lower angle of attack as a result of 

greater induced root inflow. The dynamic inflow option of RCAS over predicts the tip 

and hub region angle of attack even though the method implicitly includes the PrandtlGoldstein tip losses. Also unusual is the lower angle of attack (around 50% radius) when 

induced swirl effects are not included in the dynamic wake inflow option. 

Further comparison of the RCAS dynamic wake inflow option is shown in Figure 6 for 

wind speeds of 5, 7, and 10 m/s. The dynamic inflow option tends to under predict the 

angle of attack distribution with increasing wind speeds, except for the immediate tip and 

hub region. Also, WT_Perf over predicts the angle of attack with increasing wind speed 

as a result of the uniform inflow assumption around the annulus and the assumption of no 

interaction between annuli. 

7
12.0 

10.0 

WTPerf, 7 m/s, BEM 

LSWT, 7 m/s 

rcas, 7 m/s, BEM, tip loss 1.0 

rcas, 7 m/s, Peters & He 

8.0 

6.0 

4.0 

2.0 

0.0 

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 

r/R 

Figure 5. Angle of attack comparison with generalized dynamic wake [4]. 

24.0 

22.0 

20.0 

18.0 

16.0 

14.0 

12.0 

10.0 

8.0 

6.0 

4.0 

2.0 

0.0 

0.0 0.1 0.2 0.3 0.4 r/R 0.5 0.6 0.7 0.8 0.9 1.0 

WT_Perf 

LSWT 

RCAS, Peters & He 

10 m/s 

7 m/s 

5 m/s 

Figure 6. Angle of attack comparison for several wind speeds. 

Quasi-Steady State Results 

Angle of attack predictions at 10 m/s were generated for yaw angles of 10° and 30° at 

three blade radial stations (r/R=0.42, 0.87, and 0.97). The dynamic wake inflow model 

was used for RCAS because it is more accurate than the other inflow models. 

AeroDynAeroDyn comparisons are also provided with its dynamic wake inflow model. 

The comparisons show angle of attack versus blade azimuth. Zero blade azimuth is with 

the blade at the top of the rotor disc advancing into the wind. The advancing blade half of 

the disc would be 270°–90°; the retreating half would be 90°–270°. 

For a yaw angle of 10°, a comparison of angle of attack distribution versus blade azimuth 

is shown in Figure 7. At r/R=0.97, RCAS, AeroDyn, and LSWT all agree with Angle of Attack, deg. 

Angle of Attack, deg. 

8
30 

25 

LSWT, r/R=0.416 

AeroDyn, dynamic inflow, r/R=0.425 

RCAS, dynamic inflow, r/R=0.427 

advancing blade 

retreating blade 

advancing blade 

r/R=0.42 

r/R=0.87 

r/R=0.97 

20 

15 

10 

5 

0 

0 30 60 90 120 150 180 210 240 270 300 330 360 

Azimuth, deg. 

Figure 7. Yawed flow of 10° at a wind speed of 10 m/s. 

an angle of attack slightly higher than 6°. Moving inboard to r/R=0.87, the angle of attack 

phasing is somewhat different even though both RCAS and AeroDyn use a dynamic 

inflow formulation. LSWT appears to be in better agreement with RCAS. Also in the root 

region RCAS and LSWT are in good agreement except for a large blade/vortex 

interaction on the retreating blade. In the root region AeroDyn predicts an angle of attack 

several degrees higher than the other two methods. For higher yaw angles LSWT would 

not converge because of numerical problems resulting from a lack of a finite vortex core 

model that would limit extremely high induced velocities resulting from blade/vortex 

interactions. 

At a yaw angle of 30°, a similar comparison of RCAS and AeroDyn was done with the 

dynamic wake inflow models (see Figure 8). Also shown for comparison is a WT_Perf 

prediction with BEM inflow. Toward the tip, WT_Perf predicts a lower angle of attack. 

The dynamic inflow model in RCAS and AeroDyn results in an angle of attack several 

degrees higher. Again, RCAS and AeroDyn exhibit an unexplained magnitude and 

phasing shift of the angle of attack relative to one another. At r/R=0.87 the differences 

between the three methods are much smaller. Blade root region differences become more 

significant; most noticeable are the previously mentioned angle of attack phase shifts 

between RCAS and AeroDyn. The angle of attack distribution of AeroDyn is slightly less 

symmetrical or biased to the right. Angle of Attack, deg. 

9
30 

25 

WT_Perf, BEM 

AeroDyn, dynamic inflow 

RCAS, dynamic inflow 

advancing blade retreating blade advancing blade

r/R=0.42 

r/R=0.87 

r/R=0.97 

20 

15 

10 

5 

0 

0 30 60 90 120 150 180 210 240 270 300 330 360 

Azimuth, deg. 

Figure 8. Yawed flow of 30° at a wind speed of 10 m/s. 

The dynamic stall option in RCAS was turned on for comparative purposes. Dynamic 

stall, option 5, was used and is considered to be the most rigorous option. The dynamic 

stall model requires airfoil specific inputs for the S809 airfoil. Similar airfoil inputs from 

the program’s cambered SC 1098 airfoil, used on the Blackhawk helicopter, were chosen 

since S809 inputs were not available. With dynamic stall turned on, the primary change is 

a decrease in angle of attack and a phase shift to the right (see Figure 9). With the 

dynamic stall model turned on in AeroDyn, a similar change is observed (Figure 10). 

Dynamic stall models in both AeroDyn and RCAS are based on the Leishmann-Beddoes 

method, but AeroDyn has the airfoil inputs hardwired with no user-selected inputs. An 

overlay of the dynamic stall predicted angle of attack distributions for RCAS and 

AeroDyn is shown in Figure 11. AeroDyn 

30 

25 

20 

15 

10 

5 

0 

0 30 60 90 120 150 180 210 240 270 300 330 360 

RCAS, dynamic inflow 

RCAS, dyn stall 5 

advancing blade retreating blade advancing blade 

r/R=0.42 

r/R=0.87 

r/R=0.97 

Azimuth, deg. 

Figure 9. RCAS dynamic stall for 30 degrees yaw at a wind speed of 10 m/s. 

10 

Angle of Attack, deg. 

Angle of Attack, deg. 
predicts a higher angle of attack peak than RCAS. For AeroDyn, toward the blade root, 

the angle of attack distribution is several degrees greater from a blade azimuth of 180°– 

90°. This increase may not be related to the difference in dynamic stall models but to 

shift without the dynamic stall model. 

30 

25 

20 

15 

10 

5 

0 

0 30 60 90 120 150 180 210 240 270 300 330 360 

AeroDyn, dynamic inflow 

AeroDyn, Beddoes 

advancing blade retreating blade advancing blade 

r/R=0.42 

r/R=0.87 

r/R=0.97 

Azimuth, deg. 

Figure 10. AeroDyn dynamic stall for 30° yaw at a wind speed of 10 m/s. 

30 

25 

20 

15 

10 

5 

0 

0 30 60 90 120 150 180 210 240 270 300 330 360 

AeroDyn, Beddoes 

RCAS, dyn stall 5 

advancing blade retreating blade advancing blade 

r/R=0.42 

r/R=0.87 

r/R=0.97 

Azimuth, deg. 

Angle of Attack, deg.

Angle of Attack, deg. 

Figure 11. RCAS/AeroDyn dynamic stall, 30° yaw at a wind speed of 10 m/s. 

11
Conclusions 

Evaluation of the four aerodynamic inflow models in RCAS resulted in the following 

findings. BEM, which is used for most codes, lacks several features—Prandtl tip and hub 

loss model, induced swirl calculations, and the Glauert approximation for use at high 

thrust coefficients—needed for wind turbine analysis. Without these features, the BEM 

inflow option in RCAS over predicts the angle of attack distribution. The generalized 

dynamic wake inflow option in RCAS provided a reasonable prediction of the angle of 

attack distribution. Inherent in this model is a Prandtl-Goldstein based tip loss correction. 

Even with the tip loss correction, the local tip angle of attack is over predicted relative to 

BEM and LSWT theories. The wake inflow option does not include induced swirl effects. 

This does not appear to be a significant impediment, since the angle of attack distribution 

toward the blade root where the angle is reduced by swirl is already under predicted. 

Being a time domain, noniterative inflow model, the generalized dynamic wake is the 

only inflow model practical for unsteady inflow and aeroelasticity calculations. This 

model will also provide the lowest computational time of the four inflow models. The 

prescribed and free-wake inflow options are not as well suited for unsteady flow 

conditions because both the blade and wake vortex model, which are less compatible with 

dynamic perturbations, are discretized. The prescribed and free-wake inflow options are 

better used for axis-symmetric performance prediction and blade geometry optimization. 

They both use a basic lifting-line blade representation and the prescribed wake method 

lacks equations to simulate an expanding wind turbine wake. For axis-symmetric 

performance predictions, the LSWT is currently a better choice since it is tailored for 

wind turbine analysis. 

Recommendations 

Once the Prandtl tip/hub loss model, induced swirl, and with the Glauert approximation 

are implemented in RCAS, further validation of the BEM inflow option is needed to 

verify the angle of attack distributions. A more conventional airfoil data input format is 

needed in RCAS for wind turbine analysis. A wind turbine user’s manual with examples 

is needed to minimize confusion. Wind turbine prescribed wake equations are necessary 

for the prescribed-wake inflow option. The free-wake inflow option should be further 

explored to determine what combinations of wake parameters are suitable for wind 

turbine analysis. A dynamic stall input file is needed for a generic wind turbine airfoil. 

Currently the lack of a comprehensive wind turbine user’s manual makes RCAS difficult 

to use and results in a long and expensive learning curve. A wind turbine user’s manual 

should include several well-documented wind turbine examples along with their input 

and output files. 

In AeroDyn, for yawed flow conditions, the angle of attack asymmetry versus blade 

azimuth relative to RCAS should be investigated. In LSWT, for yawed flow conditions, a 

vortex core model is needed to limit the maximum induced velocity generated by a vortex 

filament. This should be complemented with a dynamic stall subroutine. Finally, 

predicted results should be compared with actual UAE data for the operating conditions 

investigated in this report. 

12
Acknowledgments 

The authors would like to thank Hossein Saberi from ART, Inc. for the technical support 

he provided on the inner workings of RCAS. Additional thanks go to Marshall Buhl of 

NREL for his computer support and to Mike Robinson of NREL for his guidance and 

funding of this study. 

References 

[1] Anon. RCAS Theory Manual, Version 2.0, United States (US) Army Aviation and 

Missile COMmand/AeroFlightDynamics Directorate (USAAMCOM/AFDD) Technical 

Report (TR) 02-A-005, USAAMCOM/AFDD TR 02-A-005, U.S. Army Aviation and 

Missile Command, Moffett Field, CA, June 2002. 

[2] Anon. RCAS User’s Manual, Version 2.0, United States (US) Army Aviation and 

Missile COMmand/AeroFlightDynamics Directorate (USAAMCOM/AFDD) Technical 

Report (TR) 02-A-006, USAAMCOM/AFDD TR 02-A-006. Moffett Field, CA: U.S. 

Army Aviation and Missile Command, June 2002. 

[3] Anon. RCAS Applications Manual, Version 2.0, United States (US) Army Aviation 

and Missile COMmand/AeroFlightDynamics Directorate (USAAMCOM/AFDD) 

Technical Report (TR) TR 02-A-007. Moffett Field, CA: U.S. Army Aviation and 

Missile Command, June 2002. 

[4] Jonkman, J. and Cotrell, J. “A Demonstration of the ability of RCAS to Model Wind 

Turbines,” NREL/TP-500-34632, August 2003. 

[5] Peters, D.A. and He, C. “Correlation of Measured Induced Velocities with a FiniteState Wake Model,” Journal of the American Helicopter Society, Vol. 36(3), July 1991. 

[6] Leishman, J.G. and Beddoes, T.S. “A Semi-Empirical Model for Dynamic Stall,” 

Journal of the American Helicopter Society, July 1989. 

[7] Buhl Jr., M.L.; Wright, A.D.; and Tangler, J.L. “Wind Turbine Design Codes: A 

Preliminary Comparison of the Aerodynamics.” Prepared for the 17th American Society 

of Mechanical Engineers (ASME) Wind Energy Symposium, January 12-15, 1998, Reno, 

Nevada. NREL/CP-500-23975. Golden, CO: National Renewable Energy Laboratory, 

December 1997. 

[8] Laino, D.J. and Hansen, A.C. User’s Guide to the Wind Turbine Dynamics Computer 

Programs YawDyn, Windward Engineering, January 2003. 

[9] Laino, D.J. and Hansen, A.C. User’s Guide to the Wind Turbine Aerodynamics 

Computer Software AeroDyn, Windward Engineering, December 2002. 

13
[10] Kocurek, D, “Lifting Surface Performance Analysis for Horizontal Axis Wind 

Turbines,” SERI/STR-217-3163, 1987. 

[11] Hand, M.M.; Simms D.A.; Fingersh, L.J.; Jager, D.W.; Cotrell, J.R.; Schreck, S.; 

and Larwood, S.M. Unsteady Aerodynamics Experiment Phase VI: Wind Tunnel Test 

Configurations and Available Data Campaigns. NREL/TP-500-29955. Golden, CO: 

National Renewable Energy Laboratory, December 2001. 

[12] Somers, D.M., Design and Experimental Results for the S809 Airfoil, NREL/SR440-6918. Golden, CO: National Renewable Energy Laboratory, 1997. 

[13] Tangler, J.L., “The Nebulous Art of Using Wind Tunnel Airfoil Data for Predicting 

Rotor Performance,” Wind Energy, Vol. 5, No. 2/3, April-September 2002. 

Appendix: Sample Input Files 

RCAS Airfoil Data Set (S809.C81) 

180. 0. 

-172.5 .78 

-161. .62 

-147. 1. 

-129. 1. 

-49. -1.18 

-39. -1.18 

-21. -.8 

0. 0. 0. 0. 0. 0. 

.78 .78 .78 .78 .78 .78 

.62 .62 .62 .62 .62 .62 

1. 1. 1. 1. 1. 1. 

1. 1. 1. 1. 1. 1. 

-1.18 -1.18 -1.18 -1.18 -1.18 -1.18 

-1.18 -1.18 -1.18 -1.18 -1.18 -1.18 

-.8 -.81 -.83 -.85 -.85 -.85 

-16.5 -1.007 -1.007 -.944 -.96 -.965 -.965 -.965 

-15. -1.19 -1.19 -1.09 -1.055 -.99 -.98 -.98 

-14. -1.333 -1.333 -1.22 -1.096 -1. -.97 -.97 

-13. -1.334 -1.334 -1.28 -1.12 -1. -.96 -.96 

-12. -1.255 -1.255 -1.26 -1.13 -1. -.947 -.94 

-11. -1.161 -1.161 -1.19 -1.12 -.994 -.93 -.923 

-10. -1.055 -1.055 -1.01 -1.082 -.985 -.91 -.90 

-8. -.844 

-6. -.633 

-4.1 -.4 

-2.1 -.16 

0. 0.07 

2.1 .30 

4.1 .55 

6.1 .79 

8.2 .90 

10.1 .94 

11.2 .93 

12.2 .97 

13.3 1.0 

14.2 1.02 

15.2 1.03 

16.2 1.01 

18.1 .9 

19.2 .78 

30.0 1.0 

-.844 -.88 -.907 -.922 -.87 -.84 

-.633 -.66 -.684 -.741 -.77 -.75 

-.4 -.4 -.4 -.4 -.4 -.4 

-.16 -.16 -.16 -.16 -.16 -.16 

0.07 0.07 0.07 0.07 0.07 0.07 

.30 .30 .30 .30 .30 .30 

.55 .55 .55 .55 .55 .55 

.79 .79 .79 .79 .79 .79 

.90 .90 .90 .90 .90 .90 

.94 .94 .94 .94 .94 .94 

.93 .93 .93 .93 .93 .93 

.97 .97 .97 .97 .97 .97 

1.0 1.0 1.0 1.0 1.0 1.0 

1.02 1.02 1.02 1.02 1.02 1.02 

1.03 1.03 1.03 1.03 1.03 1.03 

1.01 1.01 1.01 1.01 1.01 1.01 

.9 .9 .9 .9 .9 .9 

.78 .78 .78 .78 .78 .78 

1.0 1.0 1.0 1.0 1.0 1.0 

14
129. -1. -1. -1. -1. -1. -1. -1. 

147. -1. -1. -1. -1. -1. -1. -1. 

161. -.62 -.62 -.62 -.62 -.62 -.62 -.62 

172.5 -.78 -.78 -.78 -.78 -.78 -.78 -.78 

180. 0. 0. 0. 0. 0. 0. 0. 

0. .18 .28 .38 .48 .62 .72 

-180. .022 .022 .022 .022 .022 .022 .022 

-175. .062 .062 .062 .062 .062 .062 .062 

-170. .132 .132 .132 .132 .132 .132 .132 

-165. .242 .242 .242 .242 .242 .242 .242 

-160. .302 .302 .302 .302 .302 .302 .302 

-140. 1.042 1.042 1.042 1.042 1.042 1.042 1.042 

-120. 1.652 1.652 1.652 1.652 1.652 1.652 1.652 

-110. 1.852 1.852 1.852 1.852 1.852 1.852 1.852 

-100. 2.022 2.022 2.022 2.022 2.022 2.022 2.022 

-90. 2.022 2.022 2.022 2.022 2.022 2.022 2.022 

-80. 1.962 1.962 1.962 1.962 1.962 1.962 1.962 

-70. 1.842 1.842 1.842 1.842 1.842 1.842 1.842 

-60. 1.662 1.662 1.662 1.662 1.662 1.662 1.662 

-50. 1.392 1.392 1.392 1.392 1.392 1.399 1.392 

-30. .562 .562 .562 .562 .562 .562 .562 

-21. .332 .332 .332 .332 .332 .332 .332 

-16. .155 .155 .181 .207 .235 .257 .274 

-15. .102 .102 .148 .181 .209 .233 .252 

-14. .038 .038 .099 .146 .180 .212 .233 

-13. .0264 .0264 .0455 .094 .148 .191 .216 

-12. .022 .022 .030 .06 .111 .164 .198 

-11. .0196 .0196 .0232 .038 .078 .135 .17 

-10. .0174 .0174 .0189 .0259 .053 .105 .145 

-9. .0154 .0154 .0159 .0187 .0351 .077 .122 

-8. .0138 .0138 .0138 .0147 .0220 .053 .101 

-7. .0122 .0122 .0122 .0123 .0141 .035 .082 

-6. .011 .011 .011 .011 .011 .0212 .0615 

-5. .01 .01 .01 .01 .01 .0132 .038 

-4.1 .0127 .0127 .0127 .0127 .0127 .0127 .0127 

-2.1 .009 .009 .009 .009 .009 .009 .009 

0. .0085 .0085 .0085 .0085 .0085 .0085 .0085 

2.1 .0088 .0088 .0088 .0088 .0088 .0088 .0088 

4.1 .0088 .0088 .0088 .0088 .0088 .0088 .0088 

6.1 .009 .009 .009 .009 .009 .009 .009 

8.2 .0167 .0167 .0167 .0167 .0167 .0167 .0167 

10.2 .0231 .0231 .0231 .0231 .0231 .0231 .0231 

11.2 .0236 .0236 .0236 .0236 .0236 .0236 .0236 

12.2 .0368 .0368 .0368 .0368 .0368 .0368 .0368 

13.3 .0551 .0551 .0551 .0551 .0551 .0551 .0551 

14.2 .0618 .0618 .0618 .0618 .0618 .0618 .0618 

15.2 .0705 .0705 .0705 .0705 .0705 .0705 .0705 

16.2 .088 .088 .088 .088 .088 .088 .088 

18.1 .1325 .1325 .1325 .1325 .1325 .1325 .1325 

19.2 .3474 .3474 .3474 .3474 .3474 .3474 .3474 

30. .500 .500 .500 .500 .500 .500 .500 

50. 1.392 1.392 1.392 1.392 1.392 1.392 1.392 

60. 1.662 1.662 1.662 1.662 1.662 1.662 1.662 

70. 1.842 1.842 1.842 1.842 1.842 1.842 1.842 

80. 1.962 1.962 1.962 1.962 1.962 1.962 1.962 

90. 2.022 2.022 2.022 2.022 2.022 2.022 2.022 

100. 2.022 2.022 2.022 2.022 2.022 2.022 2.022 

15
110. 1.852 1.852 1.852 1.852 1.852 

120. 1.652 1.652 1.652 1.652 1.652 

140. 1.042 1.042 1.042 1.042 1.042 

160. .302 .302 .302 .302 .302 

165. .242 .242 .242 .242 .242 

170. .132 .132 .132 .132 .132 

175. .062 .062 .062 .062 .062 

180. .022 .022 .022 .022 .022 

.20 .30 .40 .50 .6 

-180. 0. 0. 0. 0. 0. 

-170. .4 .4 .4 .4 .4 

-165. .3 .3 .3 .3 .3 

-160. .3 .3 .3 .3 .3 

-135. .5 .5 .5 .5 .5 

-90. .5 .5 .5 .5 .5 

-30. .174 .184 .196 .214 .235 

-23. .112 .118 .128 .144 .157 

-16. .073 .078 .086 .097 .108 

-15. .054 .065 .073 .084 .097 

-14. 0. .027 .054 .068 .086 

-13. 0. .0015 .025 .05 .074 

-12. 0. 0. .002 .03 .06 

-11. 0. 0. -.003 .014 .046 

-10. 0. 0. -.0015 .002 .032 

-9. 0. 0. 0. -.003 .016 

-8. 0. 0. 0. -.004 .005 

-7. 0. 0. 0. 0. -.004 

-6. 0. 0. 0. 0. -.003 

-4. 0. 0. 0. 0. 0. 

-3. 0. 0. 0. 0. 0. 

-2. 0. 0. 0. 0. 0. 

-1. 0. 0. 0. 0. 0. 

0. 0. 0. 0. 0. 0. 

1. 0. 0. 0. 0. 0. 

2. 0. 0. 0. 0. 0. 

3. 0. 0. 0. 0. 0. 

4. 0. 0. 0. 0. 0. 

6. 0. 0. 0. 0. .003 

7. 0. 0. 0. 0. .004 

8. 0. 0. 0. .004 -.005 

9. 0. 0. 0. .003 -.016 

10. 0. 0. .0015 -.002 -.032 

11. 0. 0. .003 -.014 -.046 

12. 0. 0. -.002 -.03 -.06 

13. 0. -.0015 -.025 -.05 -.074 

14. 0. -.027 -.054 -.068 -.086 

15. -.054 -.065 -.073 -.084 -.097 

16. -.073 -.078 -.086 -.097 -.108 

23. -.112 -.118 -.128 -.144 -.157 

30. -.174 -.184 -.196 -.214 -.235 

90. -.5 -.5 -.5 -.5 -.5 

135. -.5 -.5 -.5 -.5 -.5 

160. -.3 -.3 -.3 -.3 -.3 

165. -.3 -.3 -.3 -.3 -.3 

170. -.4 -.4 -.4 -.4 -.4 

180. 0. 0. 0. 0. 0. 

1.852 1.852 

1.652 1.652 

1.042 1.042 

.302 .302 

.242 .242 

.132 .132 

.062 .062 

.022 .022 

.7 .75 .8 

0. 0. 0. 

.4 .4 .4 

.3 .3 .3 

.3 .3 .3 

.5 .5 .5 

.5 .5 .5 

.25 .264 .277 

.171 .183 .206 

.117 .137 .176 

.111 .133 .173 

.103 .127 .167 

.093 .122 .163 

.083 .116 .157 

.074 .108 .149 

.065 .10 .142 

.054 .089 .132 

.041 .082 .123 

.0275 .072 .1125 

.016 .0625 .10 

.005 .04 .076 

-.0025 .026 .0665 

0. 

0. 

0. 

0. 

0. 

.0025 

-.005 

-.016 

.013 .053 

.0035 .033 

0. 0. 

-.0035 -.033 

-.013 -.053 

-.026 -.0665 

-.04 -.076 

-.0625 -.1 

-.0275 -.072 -.1125 

-.041 -.082 -.123 

-.054 -.089 -.132 

-.065 -.1 -.142 

-.074 -.108 -.149 

-.083 -.116 -.157 

-.093 -.122 -.163 

-.103 -.127 -.167 

-.111 -.133 -.173 

-.117 -.137 -.176 

-.171 -.183 -.206 

-.250 -.264 -.277 

-.5 -.5 -.5 

-.5 -.5 -.5 

-.3 -.3 -.3 

-.3 -.3 -.3 

-.4 -.4 -.4 

0. 0. 0. 

.9 

0. 

.4 

.3 

.3 

.5 

.5 

.298 

.232 

.200 

.195 

.189 

.184 

.176 

.17 

.163 

.154 

.145 

.136 

.125 

.102 

.087 

.07 

.045 

0. 

-.045 

-.07 

-.087 

-.102 

-.125 

-.136 

-.145 

-.154 

-.163 

-.17 

-.176 

-.184 

-.189 

-.195 

-.20 

-.232 

-.298 

-.5 

-.5 

-.3 

-.3 

-.4 

0. 

16
NACA0012 for Puma 

from Bousman, US Army, October 1988 

corrected cd typo at alpha=-10; October 1988 

RCAS Input File 

! ********************************************** 

! *** Rotor of CER Wind Turbine *** 

! *** English Units *** 

! *** 2 Rigid blades *** 

! *** 0.0 deg precone *** 

! *** Table lookup aerodynamics *** 

! *** no dynamic Inflow *** 

! *** Steady state *** 

! ********************************************** 

! 

MENU RCASROOT 

! Reinitialize/Clean RDB

11 

E 

! Initialize/Load screen ... 

1 

! Return to command mode 

COMMAND 

!====================================================================== 

!============================ Unit System =============================

!====================================================================== 

S UNITSYSTEM 

! Unity System Name

! ENGLISH, SI 

a ENGLISH 

!====================================================================== 

!============================ MODEL =================================== 

!====================================================================== 

S SUBSYSIDS 

! List subsystem IDs which must be unique; one ID per row.

a rotorss 

S GFRAMEORIG 

! G frame origin of the node to which the G frame is attached. 

! Primitive Active Degrees of Freedom

! Subsystem Structure Node Translational Rotational 

! Name Name ID X Y Z X Y Z 

a rotorss dtrain 51 0 0 0 0 0 0 

S SSORIGIN 

! Subsystem Origin Coordinates 

17
-- -- -- -- -- -- 

-- -- -- -- -- -- 

! Name x y z 

a rotorss 0 0 0 

S SSORIENT 

! Subsystem rotation 1 rotation 2 rotation 3 

! Name axis angle(deg) axis angle(deg) axis angle(deg)

a rotorss 2 90 0 0 0 0 

S CONTROLMIXER 

! Bedplate Control

! Cont. Control ------- Coefficients for Pilot Control --------

! ID bias Coll. Lat. Long. Pedal Throt 

! val0 b1_pitch b2_pitch b3_pitch cont4 cont5 

a 1 0 .017453 0 0 0 0 

a 2 0 0 .017453 0 0 0 

!====================================================================== 

!============================ SUBSYSTEM =============================== 

! ROTOR 

!====================================================================== 

S SELSUBSYS 

! Select a subsystem. Note that all the following data will pertain

! to this subsystem until another subsystem is selected.

a rotorss 

S SUBSYSTYP 

! Select subsystem type.

! 1=rotor, 2=fuselage, 3=control

a 1 

S SUBSYSCOMP 

! List the names of the primitive structures for the subsystem.

! Primitive Structure 

! Name 

a dtrain 

a blade1 

a blade2 

S CORNODE 

! identify center node for the rotor subsystem

! Prim_str_ID Node_ID 

a dtrain 51 

S BLADECOMP 

! Blade Primitive Structure Name(s)

! Index 1 2 3 4 5 6 7 

a 1 blade1 

a 2 blade2 

S PSORIGIN 

! Primitive Primitive Origin Offset

! Name x y z 

a dtrain 0 0 0 

a blade1 0 0 0 

a blade2 0 0 0 

S PSORIENT 

18
! Primitive rotation 1 rotation 2 rotation 3 

! Name axis angle(deg) axis angle(deg) axis angle(deg)

a dtrain 3 0 0 0 0 0 

a blade1 3 0 2 0 0 0 

a blade2 3 -180 2 0 0 0 

S ROTORPARAM 

! Rotor Rotational Speed (rad/sec)

a 7.5372E-00 

!====================================================================== 

!========================= PRIMITIVE STRUCTURE ======================== 

! dtrain 

!====================================================================== 

S PRIMITIVEID 

! Select a primitive structure

! Primitive structure_id 

a dtrain 

S ELDATASETID 

! Select an element property data set.

! Data set_id 

a wtprop 

S FENODE 

! Specify the node ID and its coordinates wrt Prim. Structure

! Node Node Coordinates 

! ID x y z 

a 51 0 0 0 ! Base of the lss 

a 57 0 0 0 ! hub node 

a 61 0 0 0 ! dummy node 

S RIGIDBAR 

! Element Node1 Node2 Center of gravity offset

! ID ID ID X Y Z 

a 1 51 57 0 0 0 

! dummy dof

!At least 1 dof is needed throughout the system

S SLIDE 

! Elem. Node1 Node2 Slide Free or Spring Damper

! ID ID ID Axis Controlled Constant Constant 

a 15 51 61 x 0 .01 .14 

S RBMELE 

! Element Node Property

! ID ID ID 

a 16 61 61 !dummy mass ( 1.e-4 slug ) 

!====================================================================== 

!========================= PRIMITIVE STRUCTURE ======================== 

! WIND TURBINE BLADE 1 

!====================================================================== 

S PRIMITIVEID 

! Select a primitive structure 

19
! Primitive structure_id 

a blade1 

S ELDATASETID 

! Select an element property data set.

! Data set_id 

a wtprop 

S FENODE 

! Specify the node ID and its coordinates wrt PS

! Node Node Coordinates (feet)

! ID x y z 

a 1 0.000 0 0 ! Blade root Node 

a 2 1.381 0 0 ! Hinge offset

a 3 1.381 0 0 ! Pitch hinge /bearing

a 20 16.5 0 0 ! Blade tip node 

S RIGIDBAR 

! Element Node1 Node2 Center of gravity offset

! ID ID ID X Y Z 

a 1 1 2 0 0 0 ! Hinge offset

a 2 3 20 7 0 0 ! rigid blade

N 

! Element Element Inertia Terms 

! ID Mass Ixx Ixy Ixz Iyy Iyz Izz 

a 2 50 10 0 0 10000 0 10010 ! blade prop 

S HINGE 

! Elem. Node1 Node2 Hinge Free or Spring Damper

! ID ID ID Type Controlled Constant Constant 

a 20 2 3 P 1 0 0 !Control br. 

S CONTROLCONNECT 

! Control Swashplate Swashplate Element Type Element 

! ID or Direct Phase(deg) (HIN/AUX/MLD ...) or ACP ID 

a 1 DIRECT 0.0 HIN 20 

!====================================================================== 

!========================= Connect Primitives ========================= 

!====================================================================== 

S CONNCONST 

! constraint ID, DOFL( PS name, node ID ), DOFR( PS name, node ID)

a 1 blade1 1 dtrain 57 

a 2 blade2 1 dtrain 57 

!====================================================================== 

!========================= Copy Primitives ============================

! blade1 to blade2 

!====================================================================== 

S PRIMIT 

! Copy primitive structures

a 1 blade1 blade2 

EXIT 

COMMAND 

20
copyprimstruct 

!====================================================================== 

!========================= PRIMITIVE STRUCTURE ======================== 

! WIND TURBINE BLADE 2 

!====================================================================== 

S PRIMITIVEID 

! Select a primitive structure

! Primitive Structure Name(s)

BLADE2 

S CONTROLCONNECT 

! Control Swashplate Swashplate Element Type Element 

! ID or Direct Phase(deg) (HIN/AUX/ENG ...) or ACP ID 

D 1 

A 2 DIRECT 0.0 HIN 20 

====================================================================== 

!======================== STRUCTURAL PROPERTIES ======================= 

! ROTORSS 

!====================================================================== 

S ELEPROPID 

! List the names of element property data sets.

! element_prop_ID

a wtprop 

S RBMPRP 

! Prop mass, cg offset Moment of Inertia 

! ID x, y, z Ixx, Ixy, Ixz, Iyy, Iyz, Izz 

a 61 .0001 0 0 0 0 0 0 0 0 0 

!dummy 

!====================================================================== 

!============================== Airfoil Data ========================== 

!====================================================================== 

S AIRFOIL 

! Airfoil Quasi Steady Airloads

! ID 2D Table File Name 

a bladeaf S809.C81 

a bladeaf2 S809.C81 

N 

! Airfoil -- Linear Airfoil Coefficients -- Zero Lift Angle

! ID C_radial CL_a CD CM of Attack (rad)

a bladeaf 0 6.28 0.01 -0.01 3.0 

a bladeaf2 0 5.78 0.008 0.0 0.0 

!====================================================================== 

!========================== Aerodynamic model =========================

!====================================================================== 

S AEROMODCOMP 

21

c 
! List of Supercomponent of the system

a rotorsc 

S SCORIGIN 

! Supercomponent Origin Coordinates

! Name x y z 

a rotorsc 0 0 0 

S SCORIENT 

! Supercomponent rotation 1 rotation 2 rotation 3 

! Name axis angle(deg) axis angle(deg) axis angle(deg)

a rotorsc 2 90 0 0 0 0 

!====================================================================== 

!======================= Rotor Aerodynamic model ======================

! Wind Turbine 

!====================================================================== 

S AEROSUPCOMPID 

! Supercomponent name to be define or modified

a rotorsc 

S SUPCMPTYP 

! 1 => rotor, 2 => wing, 3 => body, 4=> aux rotor

a 1 

S COMPID 

! List the Components which comprise the Supercomponent

! Component Primitive CP Root Blade tip

! Name(s)

a adblade1 

a adblade2 

S CPORIGIN 

! Component

! Name 

a adblade1 

a adblade2 

S CPORIENT 

! Component

! Name 

a adblade1 

a adblade2 

S INFLOW 

Structure El_id node_id 

blade1 0 20 

blade2 0 20 

Component Origin Offset

x y z 

0 0 0 

0 0 0 

rotation 1 rotation 2 rotation 3 

axis angle(deg) axis angle(deg) axis angle(deg)

3 0 2 0 0 0 

3 -180 2 0 0 0 

! 0. No inflow (wings).

! 1. Uniform momentum inflow (half wings and rotors)

! 2. Uniform momentum inflow (full wings)

! 3 Peters and He inflow model (rotors only).

! 5. Alternate Prescribed vortex wake ( only rotors).

! 6. Free vortex Wake (Only Rotor)

a 7 

S AEROPTION 

! Yawed Tip Linear Nonlinear Linear 

Compress 

22
! Flow Loss Unsteady Unsteady/Dyn Stall Airfoil -

ibility

! Effects Option Effects Leishman-beddos/Onera Coeffs Effects 

! (0:1) (0:1) (0:1) (0:6) (0:1) (0:1)

a 0 1 0 0 0 0 

S TIPLOSS 

! Radial Location 

! for Zero Lift 

! (nondim)

a 1.00 

S THRUSTAVE 

! thrust ave option, no. time steps, initial thrust, no. Revs for TPP

averaging

a 2 72 500 72 

S SUPCMPTOSS 

! Subsystem name for the current supercomponent

a rotorss 

!====================================================================== 

!==================== Aerodynamic Component ===========================

! ADBLADE1 

!====================================================================== 

S AEROCOMPID 

! Component name for defining or modifying

a adblade1 

S COMPTYPE 

! 1 => lifting surface, 2 => body, 3=> AUX ROT 

a 1 

S AERONODE 

! Aerodynamic node ids and their coordinate wrt component

! nodes IDs x y z 

a 1 0.0000e+00 0.0000e+00 0.0000e+00 

a 2 2.9000e+00 0.0000e+00 0.0000e+00 

a 3 3.5000e+00 0.0000e+00 0.0000e+00 

a 4 4.1200e+00 0.0000e+00 0.0000e+00 

a 5 4.9500e+00 0.0000e+00 0.0000e+00 

a 6 6.4000e+00 0.0000e+00 0.0000e+00 

a 7 7.6900e+00 0.0000e+00 0.0000e+00 

a 8 9.4100e+00 0.0000e+00 0.0000e+00 

a 9 1.0450e+01 0.0000e+00 0.0000e+00 

a 10 1.2410e+01 0.0000e+00 0.0000e+00 

a 11 1.3410e+01 0.0000e+00 0.0000e+00 

a 12 1.5410e+01 0.0000e+00 0.0000e+00 

a 13 1.6410e+01 0.0000e+00 0.0000e+00 

a 14 1.6500e+01 0.0000e+00 0.0000e+00 

S AEROSEG 

! Seg. Aerodyn Node IDs Chord Airfoil ELment Twist 

! ID (Inboard)(Outboard) (ft) ID ID (rad)

a 1 2 3 1.0240e+00 bladeaf 0 -8.6400e-01 

a 2 3 4 1.9330e+00 bladeaf 0 -2.6130e-01 

a 3 4 5 2.3760e+00 bladeaf 0 -2.9960e-01 

23
a 4 5 6 2.2590e+00 bladeaf 0 -1.9430e-01 

a 5 6 7 2.1210e+00 bladeaf 0 -1.1080e-01 

a 6 7 8 1.9700e+00 bladeaf 0 -5.9300e-02 

a 7 8 9 1.8310e+00 bladeaf 0 -2.7900e-02 

a 8 9 10 1.6800e+00 bladeaf 0 -1.0100e-02 

a 9 10 11 1.5310e+00 bladeaf 0 4.3600e-03 

a 10 11 12 1.3780e+00 bladeaf 0 1.5970e-02 

a 11 12 13 1.2260e+00 bladeaf 0 2.7310e-02 

a 12 13 14 1.1710e+00 bladeaf 0 3.1240e-02 

!====================================================================== 

!====================== Copy Aero components ==========================

! blade1 to blade2 

!====================================================================== 

S AEROCO 

! Copy ID, source component, destination component

a 1 adblade1 adblade2 

EXIT 

COMMAND 

copyaerocomp 

!====================================================================== 

!====================================================================== 

! END OF MODEL DEFINITION 

!====================================================================== 

!====================================================================== 

!====================================================================== 

!========================== ANALYSIS DATA ============================= 

!====================================================================== 

S SELANALYSIS 

! Case Trim Mane Stab 

! ID (0:3) (0:1) (0:1)

a 01 2 0 0 

N 

! Case_id Case Title 

a 01 example5 

S INITCOND 

! Initial Pilot Controls 

Init ----- Scope Script -----

Cond File Name 

S NO 

! collective, lateral, longitudinal, pedal, throttle 

! b1_pitch b2_pitch b3_pitch cont4 cont5 

a -4.8 -4.8 -4.8 0.0 0.0 

S SYSTEMFLAGS 

! Global element formulation flags

! gravity, aero (1=Yes, 0=No)

a 1 1 

S AEROSTATCONST 

! Define aerostatic conditions for standard sea level 

! Spec-type, altitude, temp, air density, sound velocity 

24
a 0 0 0 0 0 

S CONSTWIND 

! Constant Wind velocity with respect to I frame in I coord.

! Vx, Vy, Vz 

a 22.97 0 0 ! ft/second 

!====================================================================== 

!==================== TRIM/PERIODIC SOLUTION DATA ==================== 

!====================================================================== 

S CONVERGETOL 

!# of # of # of -Displacement Tolerance- --Velocity ToleranceMin. 

!Trim PSol Time translation rotation translation rotation 

# of 

!Iter Iter Step (ft) (rad) (ft/sec) (rad/sec)

PS Rev 

a 10 25 72 0.001 0.001 1 0.5 

S INTEGPARAM 

!No. of| Newmark Constants| HHT | Displace. | Velocity | Relax.

!Iter. | Alpha | Delta | Param | Tol | Tol | Factor

a 20 .25 .5 -.03 1.e-5 1.e-4 1.0 

!====================================================================== 

!========================= STABILITY DATA ============================= 

!====================================================================== 

S LINEAROPTION 

! Perturb. Number of Control Gust Identical Reduction Averaging

! Delta Azim/Rev Option opt Blade Opt. Option Option

a 0.001 1 0 0 0 0 0 

S CCEANALYSIS 

!Eigenanalysis Number of Transient Frequency Mean Squared

! Option Modes Response Opt. Response Opt. Random 

Response

a 1 0 0 0 0 

S PERIODICOUTPUT 

! Row Subsystem Prim. Struc. output

! ID Name Name category

a 1 all all internal.loads 

a 2 all all airloads 

a 3 all all sys_dyn_resp 

!S SAVESC 

!! Form of SC Data Directory and File Name

!! (RDB or FILES) for SC Data 

!a RDB NASA2bld.sav 

!S RUNALLCASES 

!! Run All Cases Flag (0/1)

!a 1 

25

5 
----- 

----- ------------------------------------- 

----- --------------------------------------- 

----- ------------------------------------- 

----- 

----- ----------------------- 

---------------

------------

---------------

---------------

EXIT 

COMMAND 

MENU RUNANALYSIS 

WT_Perf Input File 

WT_Perf v2.2 input file: 

Job Title (one line) ---------------------------------------------------

WT_Perf test input file. CER/NASA Phase 4 turbine. Delft wind tunnel data. 

Input Configuration 

TRUE ECHO_INP: Echo input parameters to echo.out? 

FALSE DIMEN: Turbine parameters are dimensional? 

FALSE METRIC: Turbine parameters are metric (MKS vs FPS]? 

Output Configuration 

TRUE TABDELIM: Make output tab-delimited (fixed-width otherwise). 

TRUE WRITE_BE: Write out blade element data to bladelem.dat? 

3 PAR_ROW: Row parameter (1-rpm, 2-pitch, 3-tsr/speed). 

2 PAR_COL: Column parameter (1-rpm, 2-pitch, 3-tsr/speed). 

1 PAR_SHT: Sheet parameter (1-rpm, 2-pitch, 3-tsr/speed). 

TRUE OUT_PWR: Request output of rotor power? 

TRUE OUT_CP: Request output of Cp? 

TRUE OUT_TRQ: Request output of shaft torque? 

FALSE OUT_FLP: Request output of flap bending moment? 

TRUE OUT_THR: Request output of rotor thrust? 

Model Configuration 

20 N_SEG: Number of blade segments (entire rotor radius). 

5 SEG_FRST: First segment used in the analysis. 

20 SEG_LAST: Last segment used in the analysis. 

1 N_SECT: Number of circumferential sectors. 

50 MAX_ITER: Max number of iterations for induction factor. 

Algorithm Configuration ------------------------------------------------

TRUE VITERNA: Use Viterna post stall instead of flat plate? 

TRUE TIP_LOSS: Use the Prandtl tip loss model? 

TRUE HUB_LOSS: Use the Prandtl hub loss model? 

TRUE SWIRL: Include swirl effects? 

TRUE ADV_BRK: Use the advanced brake-state model? 

FALSE ADD_3D: Add ECN's 3D effects to Cl and Cd? 

Parametric Analysis Configuration 

4.8, 4.8, 0 PIT_ST, PIT_END, PIT_DEL: First, last, delta blade pitch (deg). 

26
----- -------------------------------------------------------- 

----- ------------------------------------------------------- 

---

72, 72, 0 OMG_ST, OMG_END, OMG_DEL: First, last, delta rotor speed. 

FALSE INP_TSR: Input speeds as TSRs?

5, 20, 1 SPD_ST, SPD_END, SPD_DEL: First, last, delta speeds. 

mps UNITS: Wind speed units (mps, fps, mph). 

Turbine Data 

2 NUM_BL: Number of blades. 

16.5 ROT_RAD: Rotor radius [length]. 

-1.63 0.0 TIPTWIST: Angle between tip chordline and rotor plane [deg]. 

0.04 0.21 0.0 CHORD, THICK, TWIST: N_SEG lines of Chord [length or 

0.04 0.21 0.0 div by radius], Thickness [length 

0.04 0.21 0.0 or div by chord], and Twist [deg]. 

0.04 0.21 6.0 

0.10657 0.21 13.4 

0.144 0.21 17.0 

0.13894 0.21 12.2 

0.13389 0.21 8.7 

0.12883 0.21 6.18 

0.12378 0.21 4.36 

0.11872 0.21 3.03 

0.11367 0.21 2.04 

0.10861 0.21 1.27 

0.10356 0.21 0.66 

0.0985 0.21 0.16 

0.09345 0.21 -0.26 

0.08839 0.21 -0.62 

0.08334 0.21 -0.94 

0.07828 0.21 -1.26 

0.07323 0.21 -1.63 

0.144 HUB_RAD: Hub radius [length or div by radius]. 

0.0 PRECONE: Precone angle, positive downwind [deg]. 

0.0 TILT: Shaft tilt (can be used as yaw if shear is zero). 

3.3333 HUB_HT: Hub height [length or div by radius]. 

Aerodynamic Data 

0.002378 RHO: Air density [mass/volume]. 

0.0 SHR_EXP: Wind shear exponent (1/7 law = 0.143). 

FALSE SEP_TABL: Are Cd and Cl tables separate? 

1, 24, 24 SEG, NCL, NCD: Segment#, #CLs, #CDs (Reuse segment NCD if 

NCL=0). 

15.24 ALF_STAL: Stall angle of attack (deg). Peak of CL curve? 

1 I_SHFT: For 3D, index of Cl curve where we depart from linear. 

-1.04 0.019 0.0095 CL, CL, CD: NCL lines of Alpha (deg), Cl, and Cd. 

-0.01 0.139 0.0094 

1.02 0.258 0.0096 

2.05 0.378 0.0099 

27
3.07 0.497 0.01 

4.1 0.617 0.01 

5.13 0.736 0.0097 

6.16 0.851 0.0095 

7.18 0.913 0.0127 

8.2 0.952 0.0169 

9.21 0.973 0.0247 

10.2 0.952 0.0375 

11.21 0.947 0.0725 

12.23 1.007 0.0636 

13.22 1.031 0.0703 

14.23 1.055 0.0828 

15.23 1.062 0.1081 

16.22 1.043 0.1425 

20.00 0.700 0.3 

30 1 0.580 

45 1 1 

90 0.1 1.6 

2, 0, 1 SEG, NCL, NCD: Segment#, #CLs, #CDs (Reuse segment NCD if NCL=0). 

3, 0, 1 SEG, NCL, NCD: Segment#, #CLs, #CDs (Reuse segment NCD if NCL=0). 

4, 0, 1 SEG, NCL, NCD: Segment#, #CLs, #CDs (Reuse segment NCD if NCL=0). 

5, 0, 1 SEG, NCL, NCD: Segment#, #CLs, #CDs (Reuse segment NCD if NCL=0). 

7, 0, 1 SEG, NCL, NCD: Segment#, #CLs, #CDs (Reuse segment NCD if NCL=0). 

8, 0, 1 SEG, NCL, NCD: Segment#, #CLs, #CDs (Reuse segment NCD if NCL=0). 

9, 0, 1 SEG, NCL, NCD: Segment#, #CLs, #CDs (Reuse segment NCD if NCL=0). 

10, 0, 1 SEG, NCL, NCD: Segment#, #CLs, #CDs (Reuse segment NCD if NCL=0). 

11, 0, 1 SEG, NCL, NCD: Segment#, #CLs, #CDs (Reuse segment NCD if NCL=0). 

12, 0, 1 SEG, NCL, NCD: Segment#, #CLs, #CDs (Reuse segment NCD if NCL=0). 

13, 0, 1 SEG, NCL, NCD: Segment#, #CLs, #CDs (Reuse segment NCD if NCL=0). 

14, 0, 1 SEG, NCL, NCD: Segment#, #CLs, #CDs (Reuse segment NCD if NCL=0). 

15, 0, 1 SEG, NCL, NCD: Segment#, #CLs, #CDs (Reuse segment NCD if NCL=0). 

16, 0, 1 SEG, NCL, NCD: Segment#, #CLs, #CDs (Reuse segment NCD if NCL=0). 

17, 0, 1 SEG, NCL, NCD: Segment#, #CLs, #CDs (Reuse segment NCD if NCL=0). 

18, 0, 1 SEG, NCL, NCD: Segment#, #CLs, #CDs (Reuse segment NCD if NCL=0). 

19, 0, 1 SEG, NCL, NCD: Segment#, #CLs, #CDs (Reuse segment NCD if NCL=0). 

20, 0, 1 SEG, NCL, NCD: Segment#, #CLs, #CDs (Reuse segment NCD if NCL=0). 

AeroDyn/YawDyn Input File 

Combined Experiment Baseline for YawDyn version 12.1 

ENGLISH Units for input and output [SI or ENGlish] 

STEADY Dynamic stall model [BEDDOES or STEADY] 

NO_CM Aerodynamic pitching moment model [USE_CM or NO_CM] 

EQUILInflow model [DYNIN or EQUIL]

SWIRL Induction factor model [NONE or WAKE or SWIRL] 

5.0000E-03 Convergence tolerance for induction factor 

28
PRAND Tip-loss model (EQUIL only) [PRANdtl, GTECH, or NONE] 

PRAND Hub-loss model (EQUIL only) [PRANdtl or NONE] 

"STEADYtt.wnd" Hub-height steady wind file 

55.0 Wind reference (hub) height. 

0.0 Tower shadow centerline velocity deficit. 

1.0 Tower shadow half width. 

0.0 Tower shadow reference point. 

2.3870E-03 Air density.

1.625e-4 KinVisc - Kinematic air viscosity 

1.0000E-03 Time interval for aerodynamic calculations. 

1 Number of airfoil files used. Files listed below: 

"S809d_Cln.dat" 

20 Number of blade elements per blade 

RELM Twist DR Chord File ID Elem Data RELM and Twist ignored by 

ADAMS (but placeholders must be present) 

0.4125 

1.2375 

2.0625 

2.8875 

3.7125 

4.5375 

5.3625 

6.1875 

0 0.825 

0 0.825 

0 0.825 

6 0.825 

13.4 0.825 

17. 0.825 

12.2 0.825 

8.7 0.825 

7.0125 6.18 0.825 

7.8375 4.36 0.825 

0.66 1 

0.66 1 

0.66 1 

0.66 1 

1.7584 1 

2.376 1 PRINT 

2.2925 1 PRINT 

2.2092 1 PRINT 

2.1257 1 PRINT 

2.0424 1 PRINT 

8.6625 3.03 0.825 1.9589 1 PRINT 

9.4875 2.04 0.825 1.8756 1 PRINT 

10.3125 1.27 0.825 1.7921 1 PRINT 

11.1375 0.66 0.825 1.7087 1 PRINT 

11.9625 0.16 0.825 1.6253 1 PRINT 

12.7875 -0.26 0.825 1.5419 1 PRINT 

13.6125 -0.62 0.825 1.4584 1 PRINT 

14.4375 -0.94 0.825 1.3751 1 PRINT 

15.2625 -1.26 0.825 1.2916 1 PRINT 

16.0875 -1.63 0.825 1.2083 1 PRINT 

Combined Experiment Baseline in ENGLISH units for AeroDyn version 12.1 

6.0 Time duration of the simulation (sec) 

60.0 Number of azimuth sectors used for integration 

2 Decimation factor for output printing 

1.0000E-02 TOLER, Trim solution tolerance (deg) 

2 Number of blades 

4.8 4.8 4.8 Initial pitch angles (deg) 

4.0 Rotor hub sling (distance from yaw axis to hub; positive downwind) (ft) 

0.0 Shaft tilt angle (deg) 

29
0.0 Rotor precone angle (deg) 

72.0 RPM, rotor speed in revolutions per minute 

0.0 PsiInit, Initial rotor position (zero for Blade 1 down) (deg) 

FIXEDYaw Model: FREE or FIXED yaw system

0.0 Initial yaw angle (deg) 

0.0 Initial yaw rate (deg/sec)

1000.0 Mass moment of inertia about yaw axis (slug-ft^2) 

0.0 YawStiff, stiffness of yaw spring (lb-ft/rad) 

0.0 YawDamp, yaw damping coefficient (lb-ft-sec) 

0.0 YawFriction, constant friction moment at yaw axis (lb-ft) 

RIGID Hub model: HINGE, TEETER or RIGID 

0.0 0.0 0.0 Initial flap angles (deg) 

0.0 0.0 0.0 Initial flap rates (deg/sec) 

0.0 RHinge, radius of rotor hub (ft) 

5.44 RBar, distance from hinge to blade c.g. (ft) 

3.34 Mass of one blade (slug) 

178.0 Mass moment of inertia of blade about hinge axis (slug-ft^2) 

1.5500E+05 Torsional stiffness of blade root spring (lbf-ft/rad) 

0.0 Teeter sling distance of teeter axis upwind of rotor apex (m) 

0.0 Free teeter angle (deg) 

0.0 Teeter stiffness, first or linear coeff. (lbf-ft/rad) 

0.0 Teeter stiffness, coeff. of deflection (lbf-ft/rad^2) 

0.0 Teeter damping coefficient (lbf-ft-sec) 

1,2,5 

1 = Horizontal wind speed at hub center, len/s. [HHWSpeed] 

2 = Horizontal wind direction at hub center, deg. [HHWDir] 

3 = Nacelle yaw angle, deg. [YawAng] 

4 = Nacelle yaw rate, deg/sec. [YawRate] 

5 = Blade azimuth angle (0 when blade 1 down), deg. [AzimAngB1D] 

6 = Blade azimuth angle (0 when blade 1 up), deg. [AzimAngB1U] 

7 = Teeter angle, deg. [TeeterAng] 

8 = Teeter rate, deg/sec. [TeeterRate] 

10 = Blade 1 flap angle, deg. [FlapAng1] 

11 = Blade 1 flap rate, deg/sec. [FlapRate1] 

12 = Blade 2 flap angle, deg. [FlapAng2] 

13 = Blade 2 flap rate, deg/sec. [FlapRate2] 

14 = Blade 3 flap angle, deg. [FlapAng3] 

15 = Blade 3 flap rate, deg/sec. [FlapRate3] 

16 = Rotor power, kW. [Power] 

17 = Rotor torque, force*len. [Torque] 

20 = Nacelle yaw moment, force*len. [YawMom] 

21 = Nacelle yaw moment, kiloforce*len. [YawMomK] 

22 = Hub moment, force*len. [HubMom] 

23 = Hub moment, kiloforce*len. [HubMomK] 

24 = Rotor thrust, force. [Thrust] 

25 = Rotor thrust, kiloforce. [ThrustK] 

30
26 = Lateral hub force, force. [HForceY] 

27 = Lateral hub force, kiloforce. [HForceYK] 

28 = Vertical hub force, force. [HForceZ] 

29 = Vertical hub force, kiloforce. [HForceZK] 

30 = Out-of-plane bending moment for blade 1, force*len. [OutPlMom1] 

31 = Out-of-plane bending moment for blade 2, force*len. [OutPlMom2] 

32 = Out-of-plane bending moment for blade 3, force*len. [OutPlMom3] 

33 = In-plane bending moment for blade 1, force*len. [InPlMom1] 

34 = In-plane bending moment for blade 2, force*len. [InPlMom2] 

35 = In-plane bending moment for blade 3, force*len. [InPlMom3] 

36 = Pitching moment for blade 1, force*len. [PitchMom1] 

37 = Pitching moment for blade 2, force*len. [PitchMom2] 

38 = Pitching moment for blade 3, force*len. [PitchMom3] 

40 = Out-of-plane bending moment for blade 1, kiloforce*len. [OutPlMom1K] 

41 = Out-of-plane bending moment for blade 2, kiloforce*len. [OutPlMom2K] 

42 = Out-of-plane bending moment for blade 3, kiloforce*len. [OutPlMom3K] 

43 = In-plane bending moment for blade 1, kiloforce*len. [InPlMom1K] 

44 = In-plane bending moment for blade 2, kiloforce*len. [InPlMom2K] 

45 = In-plane bending moment for blade 3, kiloforce*len. [InPlMom3K] 

46 = Pitching moment for blade 1, kiloforce*len. [PitchMom1K] 

47 = Pitching moment for blade 2, kiloforce*len. [PitchMom2K] 

48 = Pitching moment for blade 3, kiloforce*len. [PitchMom3K] 

S809 Airfoil, Delft data at Re=1.0 Million, Clean no roughness 

NREL/TP-442-7817 Appendix B, Viterna used aspect ratio=11 

Number of airfoil tables in this file 

.00 Table ID parameter 

15.30 Stall angle (deg) 

.00 No longer used, enter zero 

.00 No longer used, enter zero 

.00 No longer used, enter zero 

-.38 Zero lift angle of attack (deg) 

7.12499 Cn slope for zero lift (dimensionless) 

1.9408 Cn at stall value for positive angle of attack 

-.8000 Cn at stall value for negative angle of attack 

2.0000 Angle of attack for minimum CD (deg) 

.0116 Minimum CD value 

-180.00 .000 .1748 .0000 

-170.00 .230 .2116 .4000 

-160.00 .460 .3172 .1018 

-150.00 .494 .4784 .1333 

-140.00 .510 .6743 .1727 

-130.00 .486 .8799 .2132 

-120.00 .415 1.0684 .2498 

-110.00 .302 1.2148 .2779 

-100.00 .159 1.2989 .2933 

31

 1 
 -90.00 

-80.00 

-70.00 

-60.00 

-50.00 

-40.00 

-30.00 

-20.10 

-18.10 

-16.10 

-14.20 

-12.20 

-10.10 

-8.20 

-6.10 

-4.10 

-2.10 

-1.04 

-0.01 

1.02 

2.05 

3.07 

4.10 

5.13 

6.16 

7.18 

8.2 

9.21 

10.2 

11.21 

12.23 

13.22 

14.23 

15.23 

16.22 

20.00 

30.00 

40.00 

50.00 

60.00 

70.00 

80.00 

90.00 

100.00 

110.00 

120.00 

.000 

-.159 

-.302 

-.415 

-.486 

-.510 

-.494 

-.560 

-.670 

-.790 

-.840 

-.700 

-.630 

-.560 

-.640 

-.420 

-.160 

1.3080 .2936 

1.2989 .2933 

1.2148 .2779 

1.0684 .2498 

.8799 .2132 

.6743 .1727 

.4784 .1333 

.3027 .0612 

.3069 .0904 

.1928 .0293 

.0898 -.0090 

.0553 -.0045 

.0390 -.0044 

.0233 -.0051 

.0131 .0018 

.0134 -.0216 

.0090 -.0282 

0.019 0.0095 -.0346 

0.139 0.0094 -.0405 

0.258 0.0096 -.0455 

0.378 0.0099 -.0507 

0.497 0.01 -.0404 

0.617 0.01 -.0321 

0.736 0.0097 -.0281 

0.851 0.0095 -.0284 

0.913 0.0127 -.0322 

0.952 0.0169 -.0361 

0.973 0.0247 -.0363 

0.952 0.0375 -.0393 

0.947 0.0725 

1.007 0.0636 

1.031 0.0703 

1.055 0.0828 

1.062 0.1081 

1.043 0.1425 

-.0398 

-.0983 

-.1242 

-.1155 

-.2459 

-.2813 

0.700 0.30 -.3134 

.705 

.729 

.694 

.593 

.432 

.227 

.000 

-.159 

-.302 

-.415 

.4784 -.2459 

.6743 -.2813 

.8799 -.3134 

1.0684 

1.2148 

1.2989 

1.3080 

1.2989 

1.2148 

1.0684 

-.3388 

-.3557 

-.3630 

-.3604 

-.3600 

-.3446 

-.3166 

32
 130.00 -.486 .8799 -.2800 

140.00 -.510 .6743 -.2394 

150.00 -.494 .4784 -.2001 

160.00 -.460 .3172 -.1685 

170.00 -.230 .2116 -.5000 

180.00 .000 .1748 .0000 

! Steady wind file for 30 fps (or m/s) wind speed for AeroDyn 

! Time Wind Wind Vert. Horiz. Vert. LinV Gust 

! Speed Dir Speed Shear Shear Shear Speed 

0.0 22.97 0.0 0 0.0 0.0 0 0 

LSWT Input File 

2 BLADED NREL/NASA COMBINED EXPERIMENT ROTOR (cer4816D.ipt)

3.0 0.0 2.0 0.0 2.0 2.0 1.0 

1.0 

0.0 0.0 0.0 

0.0 0.0 0.0 0.0 

0.0 72.0 1.0 1.0 

5.0 1.0 16.0 1.0 

-4.8 1.0 1.0 300.0 

2.0 2.0 2.0 16.5 

2.0 12.0 1.0 180 30.0 1.0 

0.0 0.0 1.0 10.0 11.0 13.0 

2.0 3.0 0.25 2.90 4.12 

0.0 0.0 0.0 0.0 0.0 0.0 

12.0 

2.90 3.50 4.12 4.95 6.40 7.69 9.41 

10.45 12.41 13.41 15.41 16.41 

0.600 1.447 2.418 2.333 2.185 2.057 1.883 

1.778 1.581 1.480 1.276 1.175 

12.0 

2.90 3.50 4.12 4.95 6.40 7.69 9.41 

10.45 12.41 13.41 15.41 16.41 

0.0 -9.9 -20.04 -14.29 -7.98 -4.72 -2.08 

-1.12 0.02 0.48 1.35 1.78 

12.0 

2.90 3.50 4.12 4.95 6.40 7.69 9.41 

10.45 12.41 13.41 15.41 16.41 

0.0 0.0 0.0 0.0 0.0 0.0 0.0 

0.0 0.0 0.0 0.0 0.0 

11.0 

001.0 2.90 3.50 

001.0 3.50 4.12 

001.0 4.12 4.95 

001.0 4.95 6.40 

001.0 6.40 7.69 

001.0 7.69 9.41 

001.0 9.41 10.45 

001.0 10.45 12.41 

001.0 12.41 13.41 

001.0 13.41 15.41 

001.0 15.41 16.41 

33
9.0 4.0 0.25 4.12 16.50 

0.0 0.0 0.0 0.0 0.0 0.0 

12.0 

2.90 3.50 4.12 4.95 6.40 7.69 9.41 

10.45 12.41 13.41 15.41 16.41 

0.600 1.447 2.418 2.333 2.185 2.057 1.883 

1.778 1.581 1.480 1.276 1.175 

12.0 

2.90 3.50 4.12 4.95 6.40 7.69 9.41 

10.45 12.41 13.41 15.41 16.41 

0.0 -9.9 -20.04 -14.29 -7.98 -4.72 -2.08 

-1.12 0.02 0.48 1.35 1.78 

12.0 

2.90 3.50 4.12 4.95 6.40 7.69 9.41 

10.45 12.41 13.41 15.41 16.41 

0.0 0.0 0.0 0.0 0.0 0.0 0.0 

0.0 0.0 0.0 0.0 0.0 

11.0 

001.0 2.90 3.50 

001.0 3.50 4.12 

001.0 4.12 4.95 

001.0 4.95 6.40 

001.0 6.40 7.69 

001.0 7.69 9.41 

001.0 9.41 10.45 

001.0 10.45 12.41 

001.0 12.41 13.41 

001.0 13.41 15.41 

001.0 15.41 16.41 

1.0 0.0 

001.0 Blade Station 1 to 11 (stalled flat plate model)

1.0 20.0 1.0 20.0 1.0 2.0 

0.21 

1.0 

-0.01 0.139 

1.02 0.258 

2.05 0.378 

3.07 0.497 

4.1 0.617 

5.13 0.736 

6.16 0.851 

7.18 0.913 

8.2 0.952 

9.21 0.973 

10.2 0.952 

11.21 0.947 

12.23 1.007 

13.22 1.031 

14.23 1.055 

15.23 1.062 

16.22 1.043 

30.0 1.0 

45.0 1.0 

90.0 0.1 

1.0 

-0.01 0.0094 

1.02 0.0096 

34
2.05 0.0099 

3.07 0.01 

4.1 0.01 

5.13 0.0097 

6.16 0.0095 

7.18 0.0127 

8.2 0.0169 

9.21 0.0247 

10.2 0.0375 

11.21 0.0725 

12.23 0.0636 

13.22 0.0703 

14.23 0.0828 

15.23 0.1081 

16.22 0.1425 

30.0 0.5 

45.0 1.0 

90.0 1.6 

0.0 

-180.0 0.0 

180.0 0.0 

35
REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188 

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, 

gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of 

information, including suggestions for reducing the burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 

1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any 

penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 

1. REPORT DATE (DD-MM-YYYY) 2. REPORT TYPE 3. DATES COVERED (From - To) 

4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER 

5b. GRANT NUMBER 

5c. PROGRAM ELEMENT NUMBER 

6. AUTHOR(S) 5d. PROJECT NUMBER 

5e. TASK NUMBER 

5f. WORK UNIT NUMBER 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION 

REPORT NUMBER 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S) 

11. SPONSOR/MONITOR'S REPORT 

NUMBER(S) 

12. DISTRIBUTION/AVAILABILITY STATEMENT 

13. SUPPLEMENTARY NOTES 

14. ABSTRACT 

15. SUBJECT TERMS 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 

ABSTRACT 

18. NUMBER 

OF 

PAGES 

19a. NAME OF RESPONSIBLE PERSON 

a. REPORT b. ABSTRACT c. THIS PAGE 

19b. TELEPHONE NUMBER (Include area code)