L. Danielle Koch

Glenn Research Center, Cleveland, Ohio

Predicting the Inflow Distortion Tone Noise of the 

NASA Glenn Advanced Noise Control Fan With 

a Combined Quadrupole-Dipole Model

NASA/TM—2012-217673

September 2012

AIAA–2012–2196
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L. Danielle Koch

Glenn Research Center, Cleveland, Ohio

Predicting the Inflow Distortion Tone Noise of the 

NASA Glenn Advanced Noise Control Fan With 

a Combined Quadrupole-Dipole Model

NASA/TM—2012-217673

September 2012

AIAA–2012–2196

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

18th Aeroacoustics Conference

cosponsored by the American Institute of Aeronautics and Astronautics and 

the Confederation of European Aerospace Societies

Colorado Springs, Colorado, June 4–6, 2012
Acknowledgments

I would like to thank Marvin Goldstein for his guidance in understanding the details of the theoretical model. I also appreciate 

the efforts of the AeroAcoustic Propulsion Laboratory staff in obtaining the experimental data, Gary Podboy and Dan Sutliff for 

obtaining the wake measurements, and Daniel L. Tweedt for providing the computational fluid dynamics analysis. Funding for this 

research has been provided by the Subsonic Fixed Wing Project which is a part of NASA’s Fundamental Aeronautics Program.

Available from

NASA Center for Aerospace Information

7115 Standard Drive

Hanover, MD 21076–1320

National Technical Information Service

5301 Shawnee Road

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Available electronically at http://www.sti.nasa.gov

This work was sponsored by the Fundamental Aeronautics Program 

at the NASA Glenn Research Center.

Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2012-217673 1

Predicting the Inflow Distortion Tone Noise of the 

NASA Glenn Advanced Noise Control Fan With 

a Combined Quadrupole-Dipole Model 

L. Danielle Koch 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Abstract 

A combined quadrupole-dipole model of fan inflow distortion tone noise has been extended to 

calculate tone sound power levels generated by obstructions arranged in circumferentially asymmetric 

locations upstream of a rotor. Trends in calculated sound power level agreed well with measurements 

from tests conducted in 2007 in the NASA Glenn Advanced Noise Control Fan. Calculated values of 

sound power levels radiated upstream were demonstrated to be sensitive to the accuracy of the modeled 

wakes from the cylindrical rods that were placed upstream of the fan to distort the inflow. Results indicate 

a continued need to obtain accurate aerodynamic predictions and measurements at the fan inlet plane as 

engineers work towards developing fan inflow distortion tone noise prediction tools. 

Nomenclature 

Aq,s Fourier coefficient of axial distortion velocity 

aq circumferential Fourier coefficients of the axial distortion velocity profile 

AR aspect ratio 

B number of rotor blades 

b blade height 

c0 speed of sound 

c rotor chord length 

D compressibility correction factor defined by Equation (8) 

ds radial Fourier coefficients of axial distortion velocity profile 

Hp,q,s defined by Equation (2) 

H p,q,s complex conjugate of Hp,q,s

i −1

I ratio of maximum distortion velocity to mean axial velocity U 

Kp,q,s defined by Equation (3) 

Jj dimensionless circumferential location of inlet obstructions 

M axial Mach number, U/c0

Mr relative Mach number, Ur/c0

Mt rotor tip Mach number, Ut/c0

N number of upstream vanes or struts, integer 1, 2, ... 

Pp total acoustic power radiated upstream in the p

th harmonic of the blade passing frequency 

R mean radius 

S(σq ) Sears function, defined in Equation (6) 

U axial flow velocity 

Ur relative velocity, − Ut +U2

Ut cascade (rotor) velocity 

yi coordinates of source point 
NASA/TM—2012-217673 2

wi phase-locked rotor velocity field relative velocity field 

β 1− M 2

βr 1− Mr

2

Δ interblade spacing 

δ circumferential distance, BΔ

δi,j Kronecker delta 

Θp,q,s defined by Equation (4) 

θ work coefficient, −Δw2 /Ut

ρ0 background density 

σ’ half-width of Gaussian/step profile 

σq reduced frequency, qΩc

2Ur

σ ̃ dimensionless radial height of axial distortion velocity profile 

ψ defined by Equation (5) 

Ω shaft rotational frequency, 2πUt

δ

Subscripts 

i, j, k integer 1, 2, 3, ... 

s integer 0, 1, 2, ... 

p,q integer, 0, ±1, ±2, ... 

Introduction 

A combined quadrupole-dipole analytic model of fan inflow distortion tone noise was published by 

Goldstein, Dittmar, and Gelder in 1974 (Ref. 1). Their intention was to predict the upstream-radiated tone 

noise from a fan with a high-subsonic rotor tip speed that was ingesting flow distorted by the presence of 

uniformly spaced upstream struts. They chose to retain the quadrupole source term in a generalized 

version of the Ffowcs Williams and Hawkings (Refs. 2 and 3) formulation based on a previous suggestion 

of Morfey (Ref. 4), whose simplified analysis suggested that sound generated by the quadrupole term may 

be equal to or greater than the sound generated by a dipole term for axial Mach numbers of the inflow as 

low as 0.25. Indeed, upon examining the final form of the equations of the combined quadrupole-dipole 

model, Goldstein et al. noted that the dipole term was independent of the work coefficient of the fan, but 

that the quadrupole term would be greater than the dipole term for highly-loaded, low-solidity fans. A 

limited amount of experimental data accompanied the original derivation in Reference 1. 

The current paper describes an extension of the theory presented by Goldstein, et al. (Ref. 1). The 

original theory has been extended so that tone sound power levels can be calculated when obstructions are 

placed at circumferentially asymmetric locations upstream of the rotor to distort the inflow. A computer 

code called GDGK has been written based on the theory of Goldstein, Dittmar, Gelder extended and 

programmed by Koch. Computed results are compared here against data from a test conducted with the 

NASA Glenn Advanced Noise Control Fan (ANCF) in 2007. Data from the ANCF experiments is 

considered to be a partial validation of this model, as the quadrupole generation mechanism was not a 

dominant component of the inflow distortion tones for this low-speed, lightly loaded fan. 

Prediction Method 

Goldstein et al. presented a derivation of the following equations to estimate sound power of the blade 

passing frequency (BPF) harmonic tones radiated upstream of a fan ingesting distorted inflow (see pp. 12, 

and 25 to 28 of Ref. 1). Many assumptions were made to arrive at these equations; such as modeling the 
NASA/TM—2012-217673 3

fan duct as an unrolled rectangular duct, modeling the rotor potential flow field as a line of free vortices, 

and using a Gaussian function to model the wakes of the upstream stators or vanes. These original 

equations were incorporated into the first version of the computer code GDGK.v1. The first term of 

Equation (4) is associated with the quadrupole mechanism, and the second term in Equation (4) is 

associated with the dipole mechanism. 

Pp

ρ0c0

3BbΔ = (MMt)2 pMt

4 (1+ δs,0 )

Θp,q,s

2

Aq,s

2

(Mt p+ MKp,q,s)2Kp,q,s

∑ (1) 

all q and all s ≥ 0 with 

p2Mt

2 > β2 p− q

B

⎛

⎝

⎜ ⎞

⎠

⎟

2

+

σ′

2b

⎛

⎝

⎜ ⎞

⎠

⎟

2 ⎡

⎣

⎢

⎢

⎤

⎦

⎥

⎥

Hp,q,s =

p− q

B

⎛

⎝

⎜ ⎞

⎠

⎟β2 − iD MM ( ) t p+ Kp,q,s

pβr − iKp,q,s

 (2) 

Kp,q,s = p2Mt

2 − β2 p− q

B

⎛

⎝

⎜ ⎞

⎠

⎟

2

+

sΔ

2b

⎛

⎝

⎜ ⎞

⎠

⎟

2 ⎡

⎣

⎢

⎢

⎤

⎦

⎥

⎥

 (3) 

Θp,q,s ≡ −θH p,q,s( ) MMt p+ Kp,q,s + iψS( ) σq

M pB ( ) − q β2

B − Mt( ) MMt p+ Kp,q,s

⎡

⎣

⎢ ⎤

⎦

⎥ (4) 

ψ = 1

2Mr

c

Δ

⎛

⎝

⎜ ⎞

⎠

⎟ 2πAR

AR+ 2 AR+ 4

AR+ 2

⎛

⎝

⎜ ⎞

⎠

⎟

⎡

⎣

⎢

⎢

⎢

⎢

⎤

⎦

⎥

⎥

⎥

⎥

 (5) 

S(σq ) =

exp(−iσq ) 1− π2

2 1( ) + 2πσq

⎡

⎣

⎢

⎢

⎤

⎦

⎥

⎥

1+ 2πσq

 (6) 

σq = qπMt

BMr

c

Δ

⎛

⎝

⎜ ⎞

⎠

⎟ (7) 

D ≡ βr + iMMt

β2 (8) 

In order to evaluate Equation (1), it is necessary to determine values for Aq,s, the Fourier coefficients of 

the axial distortion velocity profile. Goldstein, et al. described one way in Reference 1 that is partially 

repeated here. If you assume 

Aq,s = Iaqds
NASA/TM—2012-217673 4

aq = 1

δ e−2πiqy2 /δ

0

δ

∫ f(y2 )dy2 (9) 

When the flow distortion is represented by N uniformly spaced Gaussian profiles in the circumferential 

direction such that 

f(y2 ) = exp

− y2

δ − 1+ 2 j

2N

⎛

⎝

⎜ ⎞

⎠

⎟

2

( ) σ′ 2

⎡

⎣

⎢

⎢

⎢

⎢

⎤

⎦

⎥

⎥

⎥

⎥

jδ

N

< y2 < ( ) j +1 δ

N

for j = 0,1,...N

⎧

⎨

⎪⎪

⎩

⎪

⎪

⎫

⎬

⎪⎪

⎭

⎪

⎪

 (10) 

aq = πNσ′e

−iπq

N e−π2 q2 ( ) σ′ 2

Re erf 1

2Nσ′

+ πiqσ′ ⎛

⎝

⎜ ⎞

⎠

⎟ ⎡

⎣

⎢ ⎤

⎦

⎥ for q = 0, ±N, ±2N, ... (11) 

aq = 0 for q ≠ 0, ±N, ±2N, ... (12) 

In the radial direction, 

ds = δs,0 if the flow distortion is uniform in the radial direction, or (13) 

ds = 2(−1)s

πs(1+ δs,0 )

sin(πsσ ̃ ) if the flow distortion is a square wave concentrated around the tip region (14) 

However, sound power level can also be calculated for circumferentially asymmetric obstructions in 

the inlet duct if one chooses a more general form of Equation (10), resulting in a slightly different form 

for aq, the circumferential Fourier coefficients of axial distortion velocity profile, where Jj is the 

dimensionless circumferential location of the upstream obstructions in the flow. 

f(y2 ) = exp

− y2

δ − J j

⎛

⎝

⎜ ⎞

⎠

⎟

2

( ) σ′ 2

⎡

⎣

⎢

⎢

⎢

⎢

⎤

⎦

⎥

⎥

⎥

⎥

0 ≤ y2

δ ≤1

for j = 0,1,2...N

⎧

⎨

⎪

⎩

⎪

⎫

⎬

⎪

⎭

⎪

 (15) 

aq = σ′ π

2

e−2πqiJ j e−(πqσ′)

2 erf

J j

σ′

− iπqσ′ ⎛

⎝

⎜ ⎞

⎠

⎟ + erf

1− J j + iπqσ′2

σ′

⎛

⎝

⎜ ⎞

⎠

⎟

⎡

⎣

⎢ ⎤

⎦

⎥

j≥0

∑ for all q (16) 

This model was incorporated into the second version of the computer code, GDGK.v2. Figure 1 

shows the notional differences between symmetric and asymmetrically arranged Gaussian curves that can 

be used to model the wakes. In the final form of the sound power level calculations, wake depth, width, 

radial extent, and circumferential placement are set using variables I, σ′, σ ̃ , and Jj, respectively. 

Predictions from the new GDGK code were generated for the 51-cm fan studied in Reference 1. 

Figure 2 shows the original published results and the new calculations from the GDGK.v1 and GDGK.v2 

codes. Generally, there is good agreement between the original and new predictions. Results from 

GDGK.v1 and GDGK.v2 were identical. Some of the differences between the original and new 

predictions are attributed to uncertainties in the input values for the calculations. While the original 

reports included values for most of the input quantities, the experimental value for fan inlet temperature 

was not presented which is needed to determine fan corrected speed and inflow variables. So for the new 
NASA/TM—2012-217673 5

GDGK predictions, it was assumed that the rotor speed settings were 10,666, 9,333, and 8,000 rpm; and 

that density was 0.800 kg/m3

 and acoustic speed was 336 m/s. Also, since sound power levels were not 

published in tabular form, there may be some errors in the historical values presented in Figure 2, which 

were determined by a manual inspection of the original plot. 

Experiment 

A fan inlet distortion experiment was conducted in 2007 using the NASA Glenn Advanced Noise 

Control Fan that is housed within AeroAcoustic Propulsion Laboratory (AAPL), as shown in Figure 3. 

The ANCF is 1.2 m (48 in.) in diameter and the centerline of the fan is 3.0 m (10 ft) above the floor. For 

both tests, no stator vanes were installed downstream of the rotor. The rotor had 16 blades set at a 28°

pitch angle for all test conditions. 

An Inflow Control Device (ICD) was used to condition the flow entering the fan, removing largescale turbulence and ground vortices. The inlet plane was located 0.920 m (36.2 in.) or approximately 

0.750 L/D ahead of the leading edge of the fan at the tip location. The exhaust plane was located 1.20 m 

(45.4 in.) or approximately 1.0 L/D downstream of the trailing edge of the fan at the tip location. 

Downstream of the test section, the centerbody diameter increases to 0.710 m (24.0 in.) to mimic a nozzle 

area contraction, yielding a hub-to-tip ratio of, σ = 0.500. The hub diameter at the rotor leading edge was 

0.460 m (18.0 in.), yielding a hub-to-tip ratio of, σ = 0.375. 

The inflow to the rotor was distorted by installing smooth cylindrical rods upstream of the rotor, as 

shown in Figure 4. The rods were 1.27 cm (0.500 in.) in diameter and were 31.8 cm (12.5 in.) long, 

resulting in a 6.35 cm (2.50 in.) gap between the bottom of the rods and the rotor hub. The centerline of 

the rods was 14.3 cm (5.63 in.) upstream of the rotor leading edge at the tip, or approximately one rotor 

chord length upstream. Data were recorded at three speed settings: 1400, 1800, and 2000 rpm. Four 

distortion patterns were tested in the 2007 experiment, as shown in Figure 5. A 30-rod mounting ring 

allowed rods to be placed at circumferential locations separated by increments of 12°. The experiment is 

described in more detail in References 5 to 7.

Two 15-microphone arrays were used to record the farfield sound distribution from the ANCF. 

Farfield microphone measurements were acquired synchronously with shaft speed at a rate of 256 

samples per revolution, which allow for processing up to the 128th harmonic of the shaft frequency, or 

equivalently, up to the 8th harmonic of the blade passing frequency for this test (Ref. 8). 

In-duct acoustic pressure measurements upstream and downstream of the rotor were acquired with the 

Rotating Rake system. The Rotating Rake system is a continuously rotating radial microphone rake that 

was inserted into the duct, at either the inlet entrance or exhaust exit plane. The system utilizes annular 

duct spinning mode theory and Doppler-shift physics to separate circumferential modes and the 

cylindrical wave equation solution to reduce the radial modes. It provides a complete map of the acoustic 

duct modal magnitudes and phases present in the fan duct. For these experiments the data were processed 

for the first two harmonics of blade passing frequency (Ref. 9). 

The axial and tangential velocities downstream of a cylindrical rod were experimentally measured 

with a two-component hotwire probe. The probe was installed in radial and circumferential actuators 

mounted to the outside of the duct. The maximum traverse span for the circumferential actuator was 30o. 

Data were recorded at four radial locations: 0.330 m (13.5 in.), 0.419 m (16.5 in.), 0.508 m (20.0 in.), and 

0.570 m (23.5 in.). 

Comparison of Calculated and Measured Sound Power Levels 

 Calculated values of the sound power levels radiated upstream were generated using the GDGK.v2 

code for the four configurations tested in the ANCF during the 2007 inlet distortion test. Figures 6 

through 8 show the computed and measured wakes from the rods, which were used to determine the wake 

width and depth parameters needed for the sound power level calculation. Figure 6 show the normalized 
NASA/TM—2012-217673 6

axial velocity distribution at a radial station near the tip of the rotor, R = 0.591 m (23.25 in.), which was 

the value used to determine the length of the unrolled rectangular duct modeling the fan, taken here to be 

the radius at 5 percent of the blade span from the tip. Figure 7 shows that the calculated wake depth 

decreases and the calculated wake width slightly increases as the flow approaches the inlet to the fan. 

TSWIFT, a Reynolds-averaged Navier Stokes solver was used to generate the mean flow predictions. 

Figure 8 shows predicted and measured distribution of the normalized axial velocity at a position slightly 

closer to the rotor tip ( R = 0.597 m (23.5 in.) and at an axial location of X = –0.113 m (–4.45 in.). 

Comparisons indicate that the measured wake was significantly wider and shallower than the predicted 

wake. 

Figures 9 show plots of calculated sound power levels radiated upstream as a function of blade 

passing frequency (BPF) harmonic. The measurements on these plots are from the inlet duct farfield 

microphone array. Using non-dimensional wake width (σ′ = 0.0039) and depth (I = 0.299) parameters 

based on the computational fluid dynamics (CFD) solution at X = 0.0254 m (–1.00 in.), calculated sound 

power levels were greater than measurements, showing a more gradual decrease in amplitude for the 

higher harmonics than was indicated by the experiment. However, by choosing parameters to model a 

wider, shallower wake (σ′ = 0.0060, I = 0.080) at the fan inlet, which is consistent with the measured 

trends, better agreement between calculated and measured sound power level trends can be achieved. 

Experimental data in the wake of the rods at this axial location near the rotor leading edge were not 

available. 

One may also hypothesize, given the results shown in Figure 9, that had the rods been placed closer to 

the fan leading edge, the overall levels of tone sound power levels could be significantly increased. 

Deeper and narrower wakes interacting with the rotor may raise the sound power levels of the higher 

harmonics. This may be of particular concern to aircraft and spacecraft ventilation system designers who 

may be faced with installing fans in convoluted ducts or near other system obstructions that can 

significantly distort the fan inflow. Alternately, aircraft engine designers will need accurate aerodynamic 

predictions and measurements near the fan inlet in order to conduct useful inlet duct acoustic design 

studies. 

Figure 10 through 12 compare the calculated and measured sound power levels for the 

circumferential and radial modes in the inlet duct for the 1 BPF and 2 BPF tones for the four tested 

configurations at 2000 rpm. The measurements were obtained from the Rotating Rake installed in the 

inlet to the fan. The algorithm used to process the Rotating Rake microphone signals is based on an 

annular duct model. The reader is reminded that the sound power level calculations are based on an 

unrolled rectangular duct model. These modeling differences result in the differences between the sets of 

propagating modes. Figures 10 through 12 assume a wide, shallow wake (σ′ = 0.006, I = 0.08) at the fan 

inlet. There was generally good agreement between the measured and calculated trends. 

Finally, comparison between the measured and calculated sound power levels of the fundamental tone 

for all three tested speeds and all rod configurations are shown in Figure 13. The green bars indicate the 

sound power levels computed by the combination of the dipole and quadrupole terms. The sound power 

levels of the dipole term were computed, as well as the sound power levels of the quadrupole terms, 

which also appear on Figure 13. The reader is reminded that when the quadrupole and dipole terms are 

combined, cancellation is possible. The quadrupole mechanism did not contribute significantly to the 

generation of the blade passing tones since the work coefficient parameter, θ, for this fan was small 

(θ = 0.04). The sound power level calculated from the quadrupole term did increase as fan speed 

increased. In general, the variation of the sound power level of the fundamental tone with speed was small 

and agreement between measured and calculated trends was good. The greatest differences between 

measured and calculated sound power levels are observed for all speeds of Configuration 3, warranting 

further study. Wake parameters were held constant for all the calculated results in Figure 13 (σ′ = 0.006, 

I = 0.08). 
NASA/TM—2012-217673 7

Conclusion 

A combined quadrupole-dipole model of inflow distortion tone noise, derived and initially validated 

by Goldstein, Dittmar, and Gelder in 1974 currently serves as the theoretical basis for a new Fortran 90 

computer code, GDGK. The first version of the code, GDGK.v1 embodies the original theory and can be 

used to generate estimates of the tone sound power radiated upstream of a fan ingesting distorted inflow. 

In this version of the code, it is assumed that multiple obstructions in the inlet are equally spaced in the 

circumferential direction. Good agreement was shown between calculations from the GDGK.v1 code and 

the experimental data published in the original report. 

The second version of the code, GDGK.v2 embodies an extension of the original theory. By 

representing the Fourier coefficients of the axial distortion velocity profile in a more general form, tone 

sound power level estimates can be generated when the obstructions in the fan inlet duct are placed in 

circumferentially asymmetric locations. GDGK.v2 calculations for the circumferentially asymmetric inlet 

duct obstructions were compared well against data from the 2007 ANCF inlet distortion experiments. 

Results indicated that calculated sound power levels were sensitive to the accuracy of the modeled wake. 

References 

1. Goldstein, M. E., Dittmar, J. H. and Gelder, T. F., "Combined Quadrupole-Dipole Model for Inlet 

Flow Distortion Noise from a Subsonic Fan," NASA TN-D-7676, 1974. 

2. Ffowcs Williams, J. E., Hawkings, D. L., "Theory Relating to the Noise of Rotating Machinery," 

Journal of Sound and Vibration, 10(1), July 1969, pp 10-21. 

3. Goldstein, Marvin E.: Aeroacoustics. NASA SP-346, 1974, section 4.3.1. 

4. Morfey, C. L., Tone Radiation From an Isolated Subsonic Rotor, Journal of the Acoustical Society of 

America, 49(5), 1971, pp. 1690-1692. 

5. Koch, L. D., "An Experimental Study of Fan Inflow Distortion Tone Noise," NASA/TM—2010-

215844, 2010. 

6. Koch, L. D., "Predicted and Measured Modal Sound Power Levels for a Fan Ingesting Distorted 

Inflow," AIAA–2010–3715, 2010. 

7. Koch, L. D., "Validation of the Predicted Circumferential and Radial Mode Sound Power Levels in 

the Inlet and Exhaust Ducts of a Fan Ingesting Distorted Inflow," NASA/TM—2012-217253, 2011. 

8. Loew, R. A., Lauer, J. T., McAllister, J. and Sutliff, D. L., "The Advanced Noise Control Fan," 

NASA/TM—2006-214368, 2006. 

9. Sutliff, D. L., "Rotating Rake Turbofan Duct Mode Measurement System," NASA/TM—2005-

213828, 2005. 
NASA/TM—2012-217673 8

Figure 1.—Notional Gaussian functions used to model wakes from circumferentially (a) symmetric and (b) 

asymmetric arrangements of upstream struts or vanes that can distort the flow entering a fan. The center 

location for the wakes depicted in (b) are represented in Equation (15) and (16) by variable Jj. 
NASA/TM—2012-217673 9

 Figure 3.—The Advanced Noise Control Fan in the NASA Glenn AeroAcoustic Propulsion Lab. 

Figure 2.—Predicted and measured sound power levels of the fundamental tone of a 

51-cm model fan. Predictions from the GDGK codes are compared to predictions and 

experimental data originally published by Goldstein et al., Reference 1. Calculated 

results from GDGK.v1 and GDGK.v2 were identical. 
NASA/TM—2012-217673 10

Figure 4.—Cross-sectional diagram of Advanced Noise Control Fan for the inlet distortion tests. 

Figure 5.—Circumferential locations of inlet distortion rods tested in 2007 in the ANCF 

at NASA Glenn. 
NASA/TM—2012-217673 11

Figure 6.—Contours of normalized axial velocity, U/c0, in the wake of a cylindrical rod from 

TSWIFT, a computational fluid dynamics solver. 

Figure 8.—Predicted and meas ured wake at radius 

R = 0.597 m (23.50 in) and axial location X = –

0.113 m (–4.45 in). 

Figure 7.—Predicted wakes at five axial locations at 

radius R = 0.5906 m (23.25 in) and a rotor speed of 

2000 rpm. 
NASA/TM—2012-217673 12

Figure 9.—Calculations of the sound power levels of the blade passing frequency harmonics from the 

GDGK.v2 code compared with measured far field sound power levels in the inlet region of the NASA 

Glenn Advanced Noise Control Fan (ANCF), 2000 rpm. 
NASA/TM—2012-217673 13

Figure 10.—Calculated (P1,q,s) and measured (P1,m,μ) in-duct circumferential and radial sound power levels for the 

inlet duct, 1 BPF, 2000 rpm. Horizontal dashed line indicates noise floor for the data set. Measurements were 

obtained with the ANCF Rotating Rake. 
NASA/TM—2012-217673 14

 (a) (b) 

Figure 11.—Calculated (P2,q,s) and measured (P2,m,μ) in-duct circumferential and radial sound power levels for the 

inlet duct , 2 BPF, 2000 rpm. Horizontal dashed line indicates noise floor for the data set. Measurements were 

obtained with the ANCF Rotating Rake. 
NASA/TM—2012-217673 15

 (a) (b) 

Figure 12.—Calculated (P2,q,s) and measured (P2,m,μ) in-duct circumferential and radial sound power levels for the 

inlet duct, 2 BPF, 2000 rpm. Horizontal dashed line indicates noise floor for the data set. Measurements were 

obtained with the ANCF Rotating Rake. 
NASA/TM—2012-217673 16

Figure 13.—Calculated (P1) and measured (P1) fundamental tone sound power levels for the inlet region. Symbols 

represent the sound power levels of the dipole and quadrupole term, while the green bars represent the sound 

power levels calculated by combining both the quadrupole and dipole terms. Measurements were obtained from 

the far field microphone array in the inlet region of the ANCF. 

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1. REPORT DATE (DD-MM-YYYY)

01-09-2012 

2. REPORT TYPE

Technical Memorandum 

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

Predicting the Inflow Distortion Tone Noise of the NASA Glenn Advanced Noise Control 

Fan With a Combined Quadrupole-Dipole Model 

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Koch, L., Danielle 

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

WBS 561581.02.08.03.45.02.04 

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

National Aeronautics and Space Administration 

John H. Glenn Research Center at Lewis Field 

Cleveland, Ohio 44135-3191 

8. PERFORMING ORGANIZATION

 REPORT NUMBER

E-18348 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration 

Washington, DC 20546-0001 

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NASA 

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NASA/TM-2012-217673 

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Unclassified-Unlimited 

Subject Categories: 02 and 71 

Available electronically at http://www.sti.nasa.gov 

This publication is available from the NASA Center for AeroSpace Information, 443-757-5802

13. SUPPLEMENTARY NOTES

14. ABSTRACT

A combined quadrupole-dipole model of fan inflow distortion tone noise has been extended to calculate tone sound power levels generated 

by obstructions arranged in circumferentially asymmetric locations upstream of a rotor. Trends in calculated sound power level agreed well 

with measurements from tests conducted in 2007 in the NASA Glenn Advanced Noise Control Fan. Calculated values of sound power levels 

radiated upstream were demonstrated to be sensitive to the accuracy of the modeled wakes from the cylindrical rods that were placed 

upstream of the fan to distort the inflow. Results indicate a continued need to obtain accurate aerodynamic predictions and measurements at 

the fan inlet plane as engineers work towards developing fan inflow distortion tone noise prediction tools. 

15. SUBJECT TERMS

Fans; Noise 

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