January 2010 

NASA/TM–2010-216178 

Open Rotor Noise Prediction at NASA Langley—

Capabilities, Research and Development 

F. Farassat 

Langley Research Center, Hampton, Virginia 
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January 2010 

NASA/TM–2010-216178 

Open Rotor Noise Prediction at NASA Langley—

Capabilities, Research and Development 

F. Farassat 

Langley Research Center, Hampton, Virginia 
Available from: 

NASA Center for AeroSpace Information 

7115 Standard Drive 

Hanover, MD 21076-1320 

443-757-5802 
Table of Contents

1- A Brief History of Research on the Aeroacoustics of Rotating Blade 

 Machinery at Langley

2- Noise Prediction Codes for Open Rotors Developed at NASA Langley 

 and Their Capabilities

2.1- Advanced Subsonic-Supersonic Propeller Induce Noise (ASSPIN) 

 code 

2.2- Ffowcs Williams-Hawkings with Penetrable Data Surface (FW- Hpds) 

 Code

2.3- The Fast Scattering Code (FSC)

3- Research and Development Plans

3.1- Proposed Plans for ASSPIN Code

3.2- Proposed Plans for FW- Hpds code

3.3- Proposed Plans for the Fast Scattering Code (FSC)

4- References

4.1- Main References | F. Farassat

4.2- Supplementary [S] References

NASA Technical Memorandum 216178 1
1- A Brief History of Research on the

 Aeroacoustics of Rotating Blade Machinery at

 Langley

Langley has been in the forefront of research on aircraft noise generation and

prediction since the 1930's [S1]. Some of the early researchers in this subject at

Langley were Deming, Garrick, Watkins, Hubbard and Maglieri. This research was

aided greatly with the introduction of the high speed digital computers in the 1960's

that were used both in acoustic experiments as well as in the development of

noise prediction codes. About the same time, the pace of research in the field of

aeroacoustics in universities, industry and government agencies accelerated due

to the public objection to aircraft noise both in the cabin and around the airports.

Modern digital computers have made it possible to use advanced mathematical

models to study the acoustics of propulsion systems with realistic geometry and

operating conditions. NASA scientists and engineers have contributed significantly

to aircraft noise reduction both by theory development and the use of experimental

methods.

In what follows, we will discuss the history of theoretical model development at

Langley with which the author was involved during the period 1975 to present. We

will confine ourselves to subjects of relevance to aircraft with open rotors as their

propulsion system. This would also involve the calculation of installation effects

and the noisefoot prints at various flight conditions.

The introduction of the concept of the acoustic analogy (AA) by Lighthill in 1952

[S2] was one of the most important advances in aeroacoustics which has resulted

in current high level of aircraft noise prediction technology. In 1969, Ffowcs

Williams and Hawkings presented an extension of Lighthill's jet noise equation to

the noise from turbulence in the presence of moving surfaces appropriate for

studying the acoustics of rotating machinery | helicopter rotors, propellers, fans

and open rotors [S3]. This extension is known as the Ffowcs Williams-Hawkings

(FW-H) equation. 

Let a moving surface be described implicitly by fHx, tL = 0 such that ıf = n, n is the

unit outward normal. This assumption implies that f > 0 outside the moving surface

(see Figure 1).

2 NASA Technical Memorandum 216178
Figure 1- The definition of the moving surface implicitly as fHx, tL = 0. Note

that ı f = n where n is the unit outward normal to the surface.

The Ffowcs Williams- Hawkings (FW-H) equation is

· (1) 2 p' = ∂

∂t

@r0 vn dHfLD - ∂

∂xi

@p ni dHfLD +

∂2

∂xi ∂xj

@HHfL TijD

Here and elsewhere in the paper, we will use the summation convention on the

repeated index. In this equation ·2 is the wave or DʼAlembertian operator in three

dimensional space. Also p' = c2 r' = c2Hr - r0L, c and r0 are the speed of sound

and density in the undisturbed medium, respectively. Note that p£

 can only be

interpreted as the acoustic pressure if r£ ê r0 << 1. The symbols vn, p and

Tij = r ui uj - sij +Ip£ -c2 r'M dij are the local normal velocity of the surface, the

local gage pressure on the surface (in fact p -p0), and the Lighthill stress tensor,

respectively. In the definition of the Lighthill stress tensor, sij is the viscous stress

tensor and dij is the Kronecker delta. The Heaviside and the Dirac delta functions

are denoted HHfL and dHfL, respectively. In the second term on the right of eq. (1),

we have neglected the viscous shear force over the blade surface acting on the

fluid.

The three inhomogeneous source terms on the right of Eq. (1) are known as the

thickness, loading and quadrupole sources, respectively. Note that the thickness and loading sources are surface sources while the quadrupole source is

regarded as a volume source although it can be analytically broken into volume

and surface sources [21, 23, 27, 31, 36]. This latter point of view can explain

several (old and new) mechanisms of noise generation in rotating blades some of

which have not been studied in detail, e.g., flapping wakes in the vicinity of trailing

edge.

NASA Technical Memorandum 216178 3
The three inhomogeneous source terms on the right of Eq. (1) are known as the

thickness, loading and quadrupole sources, respectively. Note that the thickness and loading sources are surface sources while the quadrupole source is

regarded as a volume source although it can be analytically broken into volume

and surface sources [21, 23, 27, 31, 36]. This latter point of view can explain

several (old and new) mechanisms of noise generation in rotating blades some of

which have not been studied in detail, e.g., flapping wakes in the vicinity of trailing

edge.

We note that we have artificially converted a nonlinear problem of noise generation

by a moving surface to a linear problem by using the acoustic analogy. All the

nonlinearities are lumped into the Lighthill stress tensor which is assumed known

from near field aerodynamic calculations. When we started working on helicopter

and propeller noise in the early seventies, because of the limitations of digital computers, the most we could expect from aerodynamic calculations was the blade

surface pressure. For this reason, using some physical reasoning, we neglected

the quadrupole volume sources in FW-H equation and concentrated on development of formulations for the prediction of thickness and loading noise. Later on, as

computers became more powerful, we included quadrupoles in our noise prediction. There was, however, another theoretical advance which led to the use of

purely surface sources to which we will turn next. 

It was Ffowcs Williams himself who proposed to use a penetrable (porous or permeable) data surface to account for nonlinearities in the vicinity of a moving surface.

We again assume that the penetrable surface defined by f Hx, tL = 0 and the fluid

velocity is denoted by u. The FW-H equation for penetrable (permeable,

porous) data surface, FW-Hpds, is: 

Ñ (2) 2 c2 r£ a Ñ2 p£ = ∂

∂t

@r0 UnD dHfL - ∂

∂xi

@Li dHfLD +

∂2

∂xi ∂xj

@Tij HHfLD

 We have used the following notations in the above equation:

Un = 1 - (3)

r

r0

vn +

r un

r0

Li = p d ij nj + r ui Hun - vnL (4)

where dij is the Kronecker delta. As in the case of eq. (1), in the first term on the

right of eq. (4), we have neglected the viscous shear force over the data surface

acting on the fluid exterior to the surface. The philosophy behind using FW-Hpds is

to locate the data surface f = 0 to enclose a moving surface, in such a way that all

quadrupoles producing non-negligible noise are included within this surface. Therefore, no volume integration of the quadrupoles outside the data surface is necessary. High resolution CFD calculation is performed in the near field region

(including turbulence simulation if broadband noise prediction is required). The

data surface used for the acoustic calculation should be located within the region

of high resolution CFD computationAs discussed in Section 3the optimal loca

4 NASA Technical Memorandum 216178
where dij is the Kronecker delta. As in the case of eq. (1), in the first term on the

right of eq. (4), we have neglected the viscous shear force over the data surface

acting on the fluid exterior to the surface. The philosophy behind using FW-Hpds is

to locate the data surface f = 0 to enclose a moving surface, in such a way that all

quadrupoles producing non-negligible noise are included within this surface. Therefore, no volume integration of the quadrupoles outside the data surface is necessary. High resolution CFD calculation is performed in the near field region

(including turbulence simulation if broadband noise prediction is required). The

data surface used for the acoustic calculation should be located within the region

of high resolution CFD computation. As discussed in Section 3, the optimal location of the data surface, particularly when vortices cross the surface, is still the

subject of research. One would like this surface to be as small as possible,

because of the computer intensive nature of aerodynamic and turbulence simulation that require fine grid sizes and small time steps. 

We have developed several equivalent solutions of the FW-H equation in the time

domain (called formulations in this report) at NASA Langley that are used to

develop two efficient codes for the prediction of the noise of rotating machinery. In

the next section we present a discussion of these formulations, computer codes

based on them and their capabilities. Note that the Fast Scattering Code (FSC)

does not depend on these formulations but is included in the next section because

we will find it useful for open rotor noise prediction when scattering of the open

rotor generated noise by fuselage and wing surfaces becomes important.

NASA Technical Memorandum 216178 5
2- Noise Prediction Codes for Open Rotors

 Developed at NASA Langley and Their

 Capabilities

The author has derived several solutions of the FW-H equation that are useful for

efficient numerical computation of the noise of rotating blades. We mention here

three formulations in the time domain valid in the near and far fields that

include only the thickness and loading sources of the FW-H equation. In chronological order, these are: 

1- Formulation 1 [1, 8, 52]: This was developed for surfaces moving at subsonic

motion if used with the Doppler singularity. It is valid for surfaces moving at transonic and supersonic speeds if at no time during the emission process the condition Mr = 1 occurs and the collapsing sphere form of the formulation is utilized [1].

Here Mr is the Mach number of the source in the radiation direction. Note that in

this section, the Mach number is always based on the speed of sound in the undisturbed medium. In the case of transonic and supersonic speeds, the multiple emission times of the source must be accounted for in the acoustic calculation. Formulation 1 is the simplest of our three formulations distinguished by an observer time

derivative before one of its two surface integrals. This time derivative must be

evaluated numerically which can be a source of numerical error.

2- Formulation 1A [7-9, S4, 52]: This result was obtained by taking the observer

time derivative of Formulation 1 inside the integral analytically and, thus, eliminating the need for taking the derivative numerically. Although, in principle, this result

can be obtained by elementary calculus (not recommended), the simplest method

of deriving it is using an identity of generalized functions for the free space Green's

function of the wave equation at the beginning of the derivation [8]. An immediate

consequence of eliminating the observer time derivative of Formulation 1 is the

increase in the complexity of the formula and the increase in the order of the

Doppler singularity from H1- MrL

-1 to H1- MrL-3

. The increase in the complexity of

the formulation does not cause any concern for numerical implementation on the

computer. But the increase in the order of the singularity increases the sensitivity

of the result near Mr = 1. However, in practice, we must switch to Formulation 3 in

the acoustic code when this situation occurs. The conditions for the validity of

Formulation 1A is similar to Formulation 1 and is used in the forms with Doppler

singularity (subsonic sources) as well as collapsing sphere (transonic and supersonic sources). An important use of Formulation 1A is in the acoustic code based

on the FW- Hpds equation.

6 NASA Technical Memorandum 216178
of deriving it is using an identity of generalized functions for the free space Greens

function of the wave equation at the beginning of the derivation [8]. An immediate

consequence of eliminating the observer time derivative of Formulation 1 is the

increase in the complexity of the formula and the increase in the order of the

Doppler singularity from H1- MrL

-1 to H1- MrL-3

. The increase in the complexity of

the formulation does not cause any concern for numerical implementation on the

computer. But the increase in the order of the singularity increases the sensitivity

of the result near Mr = 1. However, in practice, we must switch to Formulation 3 in

the acoustic code when this situation occurs. The conditions for the validity of

Formulation 1A is similar to Formulation 1 and is used in the forms with Doppler

singularity (subsonic sources) as well as collapsing sphere (transonic and supersonic sources). An important use of Formulation 1A is in the acoustic code based

on the FW- Hpds equation.

Formulation 3 [13, 16, 17, 20]: This complicated result is very difficult to derive

and requires advanced knowledge of differential geometry, general tensor analysis

and generalized functions. The formulation is valid at all speed ranges of the

source surface | subsonic, transonic and supersonic. However, because of its

complexity, it is recommended for use it of the parts of the surface for which the

condition Mr = 1 occurs. For an open rotor with blades that have sharp leading and

trailing edges in the region that run supersonically, the blade sweep can be

specified in such a manner that no singularities would appear in the acoustic

pressure signature when this formulation is used. Otherwise, one can expect the

integrable logarithmic singularity in the acoustic pressure [22, 27]. However, it

should be mentioned that the appearance of this singularity is mathematical and

can be removed by the inclusion of the quadrupole term of the FW-H equation as

shown by Farassat and Myers [38]. 

An explanation of why Formulation 3 is so complicated is given in [46]. An important test of this formulation is to compare the predicted acoustic pressure signatures and spectra from a subsonic rotating blade exclusively from Formulations 1A

and 3 under identical input data. This computation has been performed at NASA

Langley, documented but not published. The agreement of the predicted results

from the two formulations was excellent for both the thickness and loading noise.

Furthermore, this agreement also verified that both these formulations were coded

correctly in the Langley developed code ASSPIN (Advanced Subsonic - Supersonic Propeller Induced Noise). 

Some old and obsolete NASA Langley acoustic codes used Formulation 1 for high

speed propellers [6]. We currently use only Formulations 1A and 3 in our noise

prediction codes such as ASSPIN discussed in the next section. The best article to

read about how to implement these formulations most efficiently to predict the

noise of rotating blade machinery is [20].

We now turn to the description of two computer codes for open rotor noise prediction. Note that our codes are valid for an observer in the near and far fields.

The third code we discuss below is the Fast Scattering Code (FSC) which is recommended for the prediction of the effect of the scattering of the open rotor noise by

fuselage and wings of an aircraft. This phenomenon includes the important shielding effect of noise by the rigid surfaces of the aircraft known also as the installation

effect.

NASA Technical Memorandum 216178 7
We now turn to the description of two computer codes for open rotor noise prediction. Note that our codes are valid for an observer in the near and far fields.

The third code we discuss below is the Fast Scattering Code (FSC) which is recommended for the prediction of the effect of the scattering of the open rotor noise by

fuselage and wings of an aircraft. This phenomenon includes the important shielding effect of noise by the rigid surfaces of the aircraft known also as the installation

effect.

ü 2.1- Advanced Subsonic-Supersonic Propeller Induced Noise 

(ASSPIN) Code

This code was developed in mid-nineteen eighties originally for a single row of

open rotors known as propfans that operated at supersonic tip speed at cruise

condition [13, 16, 17, 20]. It can also calculate the noise of a contra-rotating propeller with equal number of blades in each row. However, the present code can

form the core of a much more capable open rotor noise prediction code by the

addition of pre- and post-processors. There is an excellent Users Manual written

by Dunn and Tarkenton [S5]. This code uses Formulation 1A and 3 in such a way

that the latter formulation is used for panels on the blades with near sonic speed.

Farassat, Padula and Dunn [20] have described the structure and the algorithms of

ASSPIN in great detail with some comparison of the predicted and measured

acoustic data for propfans. Other publications of Langley with more examples of

application of the code are [30, 34, 35]. One of the most significant tests of

ASSPIN was against the frequency domain code of Donald B. Hanson with identical blade geometry, operating conditions and blade aerodynamics. The results

with good agreement were published in the same issue of the AIAA Journal in

1992 [35, S6] 

The ASSPIN code was written in FORTRAN 77 and developed originally on a

CDC-7600 mainframe computer of NASA Langley. It runs very efficiently on a

modern scientific desktop computer. Noise footprint computations can be performed routinely in a matter of few hours and even the animation of the footprint

during the takeoff condition can be simulated in a reasonable time. Other than the

fact that the nonlinear effects are not included in this code, it is one of the most

robust, accurate and verified codes in the time domain in U.S. and, to our best

knowledge, in the world.

„ 2.1.1- Input Data to ASSPIN

1- Hot blade geometry- several options are available to users 

2- Number of blades in each row

3- Inflow angle to the rotor axis

4- Unsteady blade surface pressure

„ 2.1.2- Output Data From ASSPIN

8 NASA Technical Memorandum 216178
„

2.1.2- Output Data From ASSPIN

1- Acoustic pressure time history for a stationery observer with respect to the

ground or moving with the aircraft at uniform speed

2- Acoustic pressure spectrum for an observer moving with the aircraft at uniform

speed or the acoustic spectrum for contiguous segments of time for a stationary

observer (nonperiodic time history). 

ü 2.2- Ffowcs Williams-Hawkings with Penetrable Data Surface 

HFW - Hpds) Code

It has been known since the early days of high speed propeller noise research that

nonlinear propagation effects in the near field are important. To include the nonlinearities, as discussed in Section 1, the use of a prediction code based on the

FW- Hpds is an obvious choice. Since all the commercial airliners will fly at subsonic cruise speed in the foreseeable future, Formulation 1A is the appropriate

solution of the FW- Hpds equation to use. For an aircraft in steady rectilinear flight

(the most common situation of interest), there is a simple closed-form formula

based on the Garrick triangle construction for the computation of the retarded time

in the acoustic calculations. Thus, the development of a noise prediction code

based on FW- Hpds equation using Formulation 1A for this case is a relatively

simple task. Nark and Farassat have developed such a code at Langley and have

used it for ducted fan noise prediction [50]. It can be used for open rotors with

some additional pre- and post-processors. 

When turbulence and wakes from rotors cross the data surface, spurious acoustic

signals appear in the acoustic signature which reduce the accuracy of this method.

We will discuss in Section 3 our plans to alleviate this shortcoming. 

„ 2.2.1- Input Data to FW - Hpds Code

High resolution unsteady CFD data (static pressure, fluid density and velocity) on

the data surface must be specified.

„ 2.2.2- Output Data From FW - Hpds Code

1- Acoustic pressure time history for a observer stationary with respect to the

ground or moving with the aircraft at uniform speed

2- Acoustic pressure spectrum for an observer moving with the aircraft at uniform

speed or the acoustic spectrum for contiguous segments of time for a stationary

observer (nonperiodic time history). 

NASA Technical Memorandum 216178 9
ü 2.3- The Fast Scattering Code (FSC)

This code was developed at NASA Langley by Dunn and Tinetti based on the

equivalent source method (ESM) [S7, S8]. The theory behind the FSC is

explained well in these references. It is based on the equations of time harmonic,

linearized acoustics and the ESM is used for solving an exterior Helmholtz equation as a boundary value (BV) problem for a surface moving at uniform rectilinear

speed. The incident sound source, e.g., the open rotor noise, is Fourier analyzed

and the FSC is then used to compute the scattered noise for each frequency component. The ESM is a much more efficient method of finding the scattered noise

than other well known techniques such as the boundary element method (BEM).

The advantage comes from the fact that in ESM one does not have to deal with

singular integrals (as in the case of BEM) which require elaborate and time consuming algorithms for their evaluation. For this reason, the use of ESM in the scattering problem results in a simple and efficient code. 

The FSC has been used to study the shielding effect of the engine noise by a

wedge shaped airframe for which some experimental acoustic data were available

[S9]. It was found that the agreement between the measured and predicted acoustic data was good. It is clear from this example that the shielding effect of fuselage

and wings can be an important method of aircraft engine noise control. This effect

can only be studied and quantified by utilizing the FSC. Note that the FSC provides some simple models of incident engine noise.

The ESM requires the inversion of a large matrix whose size and memory requirement increase with frequency w. Typically, the memory needed for the code is

proportional to w4 and the computational time is proportional to w6. The proportionality constants are functions of the scattering surface area. It can be shown that on

today's scientific desktop computers with one processor, either the size of the

scattering surface must be kept small or the incident frequency must be assumed

to be low [S8]. Fast multipole method (FMM) can be used to increase the upper

limit of the frequency for the same scattering surface by a factor of 3 to 4 [S10].

However, even with the use of FMM, one is not able to calculate the scattering of

noise from a large aircraft, say the size of Boeing 777, and an incident frequency

of 10 khz on a scientific desktop computer. The FSC has been parellelized to run

on multiprocessor machines to achieve this goal. 

The FSC is written in FORTRAN and can be operated in batch mode. Version 2.0

is written for a single processor. It can also be driven by a graphical user interface

(GUI) written in C++ based on WXWidgets. Two parallel versions of the FSC have

been developed at Langley | v3.1 for shared memory machines, and v3.2 for

distributed memory machines. 

The FSC was developed for the UNIX and LINUX operating systems but it can

also be adapted for Windows and Macintosh environments. A Users Manual is

available for various versions of the code [S8].

10 NASA Technical Memorandum 216178
The FSC was developed for the UNIX and LINUX operating systems but it can

also be adapted for Windows and Macintosh environments. A Users Manual is

available for various versions of the code [S8].

We believe that FSC is the most advanced and efficient aeroacoustic code available today for computation of the scattering of incident sound by aircraft surfaces.

With parallelization to run on multiprocessor machines, it can fully meet the needs

of the aircraft and engine industry for product design, evaluation and noise reduction. 

„ 2.3.1- Input Data to FSC

1- Excitation frequency and freestream thermodynamic variables

2- Numerical parameters for determining the appropriate grid generation and solution strategies

3- The scattering surface geometries (wings, fuselages, nacelles) and liner

admittances

4- Local flow variables (density, speed of sound, and Mach number vector). Code

options include: a- no flow, b- uniform flow, c- FSC generated small perturbation

compressible flow, and d- user supplied flow

5- Complex values of incident acoustic pressure and acoustic velocity at FSC

requested locations in space and time. Code options for incident sound include: asimple point monopole(s) and dipole(s), b- FSC generated engine noise from

nacelle alone run, and c- results from external noise codes capable of producing

FSC type inputs.

6- Observer position(s): Specify arbitrary observer points or request field calculations on spheres, cylinders, rectangular volumes surrounding the scattering surface. An option for requesting take-off or flyover footprints is provided.

„ 2.3.1- Output Data From FSC

Complex values of the instantaneous acoustic pressure, velocity and intensity at

the desired observer positions or the noise footprint regions. 

NASA Technical Memorandum 216178 11
3- Research and Development Plans

It can be seen from the above presentation that Langley researchers have developed the aeroacoustic technology to study the open rotor noise generation and

reduction. The available codes are able to meet much of the need of the aircraft

and engine industry for product design, evaluation and noise control. We feel that

there are areas that are in need of further improvements. We also feel that the

aircraft and engine industry have specific problems of interest that may require

further extensions of the capabilities of our codes. We are interested to learn of

these problems. We present below some of our research and development plans

which will increase the capabilities and usefulness of our codes. 

ü 3.1- Proposed Plans for ASSPIN Code 

ASSPIN is in an advanced stage of development and we suggest that

this code be used for studying free open rotor noise. The reason is that

to use the FSC with ASSPIN output as the incident sound source, we

must be able to calculate the gradient of the acoustic pressure on all

the scattering surface. The most numerically efficient method of finding

the gradient is by an analytic method. This can be done rather easily for

Formulations 1 and 1A [54] but it is next to impossible for Formulation 3

because of its analytic complexity and the number of terms. However,

since the ASSPIN code was developed in nineteen eighties, there is a

need for upgrading some of its capabilities. We recommend the following improvements to the ASSPIN code: 

1- Improvements of the blade geometry specification- The blade geometry of

the modern open rotors is a complex three dimensional curved surface. We

require the calculation of various curvatures of the surface to use in Formulation 3.

This means that we need a surface specification with smooth second derivatives.

This task was relatively easy when NACA 2D airfoils were used by some open

rotor blade designers because analytic expressions for airfoil coordinates were

available. However, today's blade designers use advanced airfoils optimized by

CFD codes for their performance. We need to use sophisticated three dimensional

blade surface specification, e.g., NURBS, which will give us surface curvature

information for noise prediction. We have made some progress in this direction but

more work needs to be done in this area. This feature will be added as a pre-processor to ASSPIN.

2- Upgrading ASSPIN to compute the noise of contra-rotating open rotors

with unequal blade numbers and geometry in each row- Currently, ASSPIN

code can handle contra-rotating open rotors with equal number of blades on each

row and identical geometry. To treat the general case of unequal number of blades

on each row, the acoustic pressure signatures of the interaction tones must be

computed. This involves changes to the observer time step and period specifications in ASSPIN code itself

Furthermorethe part of the code for the computation

12 NASA Technical Memorandum 216178
2- Upgrading ASSPIN to compute the noise of contra-rotating open rotors

with unequal blade numbers and geometry in each row- Currently, ASSPIN

code can handle contra-rotating open rotors with equal number of blades on each

row and identical geometry. To treat the general case of unequal number of blades

on each row, the acoustic pressure signatures of the interaction tones must be

computed. This involves changes to the observer time step and period specifications in ASSPIN code itself. Furthermore, the part of the code for the computation

of the acoustic spectrum must be modified to account for the interaction tones.

This feature will also give us the ability of predicting the noise of a contra-rotating

open rotor with two rows of rotors with very different geometries (blade numbers

and blade designs). 

ü 3.2- Proposed Plans for FW - Hpds code

We have not used this code for open rotor noise prediction and what we are proposing is all new and requires further research. However, for two reasons we feel that

work on this methodology must proceed with urgency because of the important

capabilities it will provide us. First, we can include the near field nonlinear propagation effects which can be important in noise prediction. Second, this is the only

open rotor prediction method that can be linked easily to the FSC to study the

shielding effect and noise footprint changes by scattering from fuselage and wings

(see Subsection 3.3, Item 3). We, therefore, propose the following research plans: 

1- Removal of spurious signals from the computed acoustic pressure signature when eddies and wakes cross the data surface - When turbulent eddies or

the wakes from open rotors cross the data surface of the FW- Hpds code, spurious

signals appear in the acoustic pressure signature. This is a major cause of concern for the accuracy of this method. We now outline here a method to alleviate

the spurious signals. Our discussion refers to Figure 3 below.

NASA Technical Memorandum 216178 13
Figure 3- Sketch of the data surface for FW- Hpds code and the use of equivalent sources to generate the null field inside the data surface at control

points. Here we show one equivalent source and one control point for

simplicity.

We first note that in the application of this code, we specifically ignore the

quadrupoles outside the data surface because specifying these sources is not

practical. We only use surface sources in this method. When the rotor wakes cross

the data surface, we have a fluctuating quadrupole field in the exterior of the data

surface which generate the spurious signals. We have one important piece of

information about the quadrupole field from the surface data. The sum of the contributions of the quadrupoles and the surface sources inside the data surface is identically zero (null field) for all time. Therefore, we can use some discrete sources

(generally monopoles that we call equivalent sources) with unknown strengths in

specified exterior or interior locations near the area of wake crossing to produce

null field at specified control points inside the data surface. We must have, at a

minimum, as many control points as the number of equivalent sources to be able

to find the unknown strengths of the equivalent sources from a system of linear

14 NASA Technical Memorandum 216178
We first note that in the application of this code, we specifically ignore the

quadrupoles outside the data surface because specifying these sources is not

practical. We only use surface sources in this method. When the rotor wakes cross

the data surface, we have a fluctuating quadrupole field in the exterior of the data

surface which generate the spurious signals. We have one important piece of

information about the quadrupole field from the surface data. The sum of the contributions of the quadrupoles and the surface sources inside the data surface is identically zero (null field) for all time. Therefore, we can use some discrete sources

(generally monopoles that we call equivalent sources) with unknown strengths in

specified exterior or interior locations near the area of wake crossing to produce

null field at specified control points inside the data surface. We must have, at a

minimum, as many control points as the number of equivalent sources to be able

to find the unknown strengths of the equivalent sources from a system of linear

equations. Once the strengths of equivalent sources are found, the noise at any

observer position in the exterior of the data surface is found from the surface

sources as well as the equivalent sources and the spurious signals should disappear. 

The problem of finding the source strengths is almost certainly ill-posed of the

common variety seen, for instance, in solving the scattering problem using equivalent sources (as in FSC). The handling of such ill-posed problems is understood

quite well and we do not expect undue difficulties to find the strengths of the equivalent sources. 

2- Development of an algorithm to transfer CFD data to the data surface for

acoustic calculations - This is an important recurring problem in aeroacoustics.

We ask for high resolution CFD data for noise calculations and invariably the CFD

grids do not coincide with the grids on the data surface for acoustic calculations.

Using a surface generated by the CFD grids for acoustic calculations generally

does not work because we need some surface geometry information (outward

normal, etc.) that cannot be obtained easily from such a surface. The accurate

extrapolation of high resolution CFD data to the data surface presents a challenging problem that needs to be solved to make the FW- Hpds code work satisfactorily. Such an algorithm must be implemented as a preprocessor for the code.

NASA Technical Memorandum 216178 15
ü 3.3- Proposed Plans for the Fast Scattering Code (FSC)

The FSC is in the process of intensive development for NASA Langley by Dunn

and Tinetti. It has not been used for calculation of scattering of sound for an open

rotor as the incident source of sound. However, we feel that the scattering of open

rotor noise from aircraft fuselage and wings must be studied in the design stage of

the aircraft for noise control. We propose the following developments and research

plans for the FSC: 

1- Search for efficient and accurate method of storage and inversion of large

and dense matrices on multiprocessor machines - For multiprocessor

machines, the selection of an efficient storage and the inversion method of large

and dense matrices that ESM requires is a challenging problem. The accuracy of

the results and the execution time are both dependent on the method of storage

and inversion of the matrix. One criterion of the search for an algorithm is reaching

a better balance between memory and time for the very large cases. This work will

be performed by Dunn and Tinetti for NASA Langley. 

2- Development of a method for finding the pressure gradient of the incident

sound at all points of scattering surface - To satisfy the boundary condition on

the scattering surface (equality of the normal velocities of incident and scattered

acoustic pressures), one needs to know the gradient of the incident sound. This is

a very difficult problem. In the case of using ASSPIN for open rotor noise prediction, we have not been able to solve this problem yet. But for the case of FW- Hpds

code used to simulate the incident sound for open rotors, we have been able to

derive two analytic results for the acoustic pressure gradient based on Formulations 1 and 1A [54]. These are known as Formulations G1 and G1A with similar

characteristics as Formulations 1 and 1A. Either result should be coded as a postprocessor of the FW- Hpds code and thus provide the input data to the FSC. 

16 NASA Technical Memorandum 216178
4- References

ü 4.1- Main References- Publications of F. Farassat on Noise Prediction of 

Rotating Blade Machinery (Mainly Propellers and Open Rotors) 

Articles in boldface letters are significant publications of the author on the

subject of this report.

1- F. Farassat: Theory of Noise Generation from Moving Bodies with an Application to Helicopter Rotors. NASA TR R-451, December 1975

2- R. J. Pegg, B. Magliozzi and F. Farassat: Some Measured and Calculated

Effects of Forward Velocity on Propeller Noise. Presented ASME Gas Turbine

Conference and Products Show, Philadelphia, PA., March 27-31,1977. ASME

Paper No. 77-GT-70

3- F. Farassat: Discontinuities in Aerodynamics and Aeroacoustics: The

Concepts and Applications of Generalized Derivatives. Journal of Sound and

Vibration, 55(2), 165-193, 1977

4- C. K. Barton, E. F. Daniels, F. Farassat and P. A. Nystrom: Analytical Noise

Predictions: Appendix to paper entitled “Characteristics of Propeller Noise on an

Aircraft Fuselage and the Associated Interior Noise Transmission. Presented at

the 5th AIAA Aeroacoustics Conference, Seattle, WA, March 12-14, 1979

5- F. Farassat and P. A. Nystrom: Letter to the Editor - Isomʼs Thickness Noise

Formula for Rotating Blades with Finite Thickness at the Tip. Journal of Sound

and Vibration, 72(4) 550-553, 1980

6- P. A. Nystrom and F. Farassat: A Numerical Technique for Calculation of

the Noise of High Speed Propellers with Advanced Blade Geometry, NASA

TP-1662, 1980

7- F. Farassat and G. P. Succi: A Review of Propeller Discrete Noise

Prediction Technology with Emphasis on two Current Methods for Time

Domain Calculations, Journal of Sound and Vibration, 71(3), 1980

8- F. Farassat: Linear Acoustic Formulas for Calculation of Rotating Blade

Noise, AIAA Journal, 19(9), 1122-1130, September 1981

9- F. Farassat: Advanced Theoretical Treatment of Propeller Noise. Presented

at von Karman Institute Lecture Series 1982-08, Brussels, Belgium, May 24-28,

1982 

NASA Technical Memorandum 216178 17
5- F. Farassat and P. A. Nystrom: Letter to the Editor - Isoms Thickness Noise

Formula for Rotating Blades with Finite Thickness at the Tip. Journal of Sound

and Vibration, 72(4) 550-553, 1980

6- P. A. Nystrom and F. Farassat: A Numerical Technique for Calculation of

the Noise of High Speed Propellers with Advanced Blade Geometry, NASA

TP-1662, 1980

7- F. Farassat and G. P. Succi: A Review of Propeller Discrete Noise

Prediction Technology with Emphasis on two Current Methods for Time

Domain Calculations, Journal of Sound and Vibration, 71(3), 1980

8- F. Farassat: Linear Acoustic Formulas for Calculation of Rotating Blade

Noise, AIAA Journal, 19(9), 1122-1130, September 1981

9- F. Farassat: Advanced Theoretical Treatment of Propeller Noise. Presented

at von Karman Institute Lecture Series 1982-08, Brussels, Belgium, May 24-28,

1982 

10- J. S. Mixson, F. Farassat, J. D. Leatherwood, R. Prydz, and J. D. Revell: .:

Interior Noise Considerations for Advanced High-Speed Turboprop Aircraft. Journal of Aircraft, 20(9), 791-797, September 1983

11- F. Farassat, and G. P. Succi: The Prediction of Helicopter Rotor Discrete

Frequency Noise, Vertica, 7(4), 309-320, 1983

12- F. Farassat and R. M. Martin: A Note on the Tip Noise of Rotating Blades,

Journal of Sound and Vibration, 86(3), 449-453, 1983

13- F. Farassat: The Prediction of the Noise of Supersonic Propellers in Time

Domain| New Theoretical Results. Presented at the AIAA 8th Aeroacoustics

Conference, Atlanta, GA, April 11-13, 1983, AIAA Paper No. 83-0743

14- F. Farassat: The Unified Acoustic and Aerodynamic Prediction of

Advanced Propellers in the Time Domain. Presented at the AIAA/NASA 9th

Aeroacoustics Conference, AIAA Paper No. 84-2303, Williamsburg, VA, October

1984

15- F. Farassat and M. K. Myers: Some Qualitative Results on the Thickness and

Loading Noise of Rotating Blades. Journal of Sound and Vibration, 101(2), 1985,

262-266

16- F. Farassat: Theoretical Analysis of Linearized Acoustics and Aerodynamics of Advanced Supersonic Propellers. Invited lecture on Aerodynamics and

Acoustics of Propellers. AGARD-CP-366, 1985

17- F. Farassat: The Prediction of the Noise of Advanced Propellers in the

Time Domain. AIAA Journal, 24, 1986, 578-584

FFThFfWilliHkiEiFifYf

18 NASA Technical Memorandum 216178
Conference, Atlanta, GA, April 11-13, 1983, AIAA Paper No. 83-0743

14- F. Farassat: The Unified Acoustic and Aerodynamic Prediction of

Advanced Propellers in the Time Domain. Presented at the AIAA/NASA 9th

Aeroacoustics Conference, AIAA Paper No. 84-2303, Williamsburg, VA, October

1984

15- F. Farassat and M. K. Myers: Some Qualitative Results on the Thickness and

Loading Noise of Rotating Blades. Journal of Sound and Vibration, 101(2), 1985,

262-266

16- F. Farassat: Theoretical Analysis of Linearized Acoustics and Aerodynamics of Advanced Supersonic Propellers. Invited lecture on Aerodynamics and

Acoustics of Propellers. AGARD-CP-366, 1985

17- F. Farassat: The Prediction of the Noise of Advanced Propellers in the

Time Domain. AIAA Journal, 24, 1986, 578-584

18- F. Farassat: The Ffowcs Williams-Hawkings Equation | Fifteen Years of

Research, Aero and Hydro Acoustics, G. Comte-Bellot and J. E. Ffowcs Williams,

editors, Springer Verlag, 1986, 175-180

19- F. Farassat and M. K. Myers: Aerodynamics via Acoustics: Application of

Acoustic Formulas for Aerodynamic Calculations. Presented at AIAA 10th

Aeroacoustics Conference, Seattle, Washington, July 9-11, 1986

20- F. Farassat, S. L. Padula and M. H. Dunn: Advanced Turboprop Noise Prediction Based on Recent Theoretical Results. Journal of Sound and Vibration,

119(1),1987, 53-79

21- F. Farassat: Quadrupole Source in Prediction of the Noise of Rotating

Blades - A New Source Description. Presented at AIAA 11th Aeroacoustics

Conference, Sunnyvale, California, October 19-21, 1987, AIAA Paper 87-2675

22- M. K. Myers and F. Farassat: Structure and Propagation of Supersonic

Singularities from Helicoidal Sources, Presented at AIAA 11th Aeroacoustics

Conference, Sunnyvale, California, October 19-21, 1987, AIAA Paper 87-2676

23- F. Farassat and K. S. Brentner: The Uses and Abuses of the Acoustic

Analogy in Helicopter Rotor Noise Prediction. Journal of the American

Helicopter Society, 33, 1988, 29-36

24- F. Farassat and M. K. Myers: The Moving Boundary Problem for the Wave

Equation: Theory and Application, Computational Acoustics | Algorithms and

Applications, Vol. 2, D. Lee, R. L. Sternberg, and M. H. Schultz, Editors. NorthHolland, 1988, 21-44

25- F. Farassat and M. K. Myers: Extension of Kirchhoffʼs Formula to

Radiation From Moving Surfaces, Journal of Sound and Vibration, 123(3), 1988,

NASA Technical Memorandum 216178 19
Blades - A New Source Description. Presented at AIAA 11th Aeroacoustics

Conference, Sunnyvale, California, October 19-21, 1987, AIAA Paper 87-2675

22- M. K. Myers and F. Farassat: Structure and Propagation of Supersonic

Singularities from Helicoidal Sources, Presented at AIAA 11th Aeroacoustics

Conference, Sunnyvale, California, October 19-21, 1987, AIAA Paper 87-2676

23- F. Farassat and K. S. Brentner: The Uses and Abuses of the Acoustic

Analogy in Helicopter Rotor Noise Prediction. Journal of the American

Helicopter Society, 33, 1988, 29-36

24- F. Farassat and M. K. Myers: The Moving Boundary Problem for the Wave

Equation: Theory and Application, Computational Acoustics | Algorithms and

Applications, Vol. 2, D. Lee, R. L. Sternberg, and M. H. Schultz, Editors. NorthHolland, 1988, 21-44

25- F. Farassat and M. K. Myers: Extension of Kirchhoffʼs Formula to

Radiation From Moving Surfaces, Journal of Sound and Vibration, 123(3), 1988,

451-460

26- F. Farassat, and M. K. Myers: High Speed Propeller Acoustics and Aerodynamics~A Boundary Element Approach. Proceedings of the International Symposium

on Boundary Element Methods: Advances in Solid and Fluid Mechanics, East

Hartford, CT, October 2-4, 1989

27- E. De Bernardis and F. Farassat: On the Possibility of Singularities in the

Acoustic Field of Supersonic Sources when BEM is Applied to a Wave

Equation. Proceedings of the International Symposium on Boundary Element

Methods: Advances in Solid and Fluid Mechanics, East Hartford, CT, October 2-4,

1989. Appeared in the book: Boundary Element Methods in Engineering, B. S.

Annigeri and K. Tseng (Eds.), 1990, Springer-Verlag 

28- F. Farassat: The Shock Noise of High-Speed Rotating Blades~ The

Supersonic Problem. Presented at the Symposium of the International Association

for Boundary Element Methods, October 15-19, 1990

29- F. Farassat and H. Tadghighi: Can Shock Waves on Helicopter Rotors

Generate Noise? A Study of the Quadrupole Source. Presented at the Vertical

Flight Technology for the 21st Century, 46th Annual Forum and Technology

Display, American Helicopter Society, Washington, DC, May 21-23, 1990

30- M. H. Dunn and Farassat, F.: State-of-the-Art of High-Speed Propeller

Noise Prediction | A Multidisciplinary Approach and Comparison with Measured Noise Data, presented at the AIAA 13th Aeroacoustics Conference, October 22-24, 1990, Tallahassee, FL, AIAA 90-3934

31- Farassat, F.; and Myers, M. K.: An Analysis of the Quadrupole Noise

Source of High Speed Rotating Blades, Computational Acoustics | Scattering,

Gaussian Beams, and Aeroacoustics, D. Lee, A. Cakmak, R Vichnevetsky,

20 NASA Technical Memorandum 216178
28- F. Farassat: The Shock Noise of High-Speed Rotating Blades~ The

Supersonic Problem. Presented at the Symposium of the International Association

for Boundary Element Methods, October 15-19, 1990

29- F. Farassat and H. Tadghighi: Can Shock Waves on Helicopter Rotors

Generate Noise? A Study of the Quadrupole Source. Presented at the Vertical

Flight Technology for the 21st Century, 46th Annual Forum and Technology

Display, American Helicopter Society, Washington, DC, May 21-23, 1990

30- M. H. Dunn and Farassat, F.: State-of-the-Art of High-Speed Propeller

Noise Prediction | A Multidisciplinary Approach and Comparison with Measured Noise Data, presented at the AIAA 13th Aeroacoustics Conference, October 22-24, 1990, Tallahassee, FL, AIAA 90-3934

31- Farassat, F.; and Myers, M. K.: An Analysis of the Quadrupole Noise

Source of High Speed Rotating Blades, Computational Acoustics | Scattering,

Gaussian Beams, and Aeroacoustics, D. Lee, A. Cakmak, R Vichnevetsky,

Editors, Vol. 2, 1990, 227-240

32- H. Tadghighi, R. Holz, and F. Farassat: Development of a Shock Noise Prediction Code for High Speed Helicopter Rotors~ The Subsonically Moving Shock

Case, Proceedings at the AHS 47th Annual Forum & Technology Display, May

6-8, 1991, Phoenix, AZ

33- F. Farassat: On the Possibility of Strong Noise Generation by Shock Surfaces

Attached to Rotating Blades. Presented at the Sixth International Symposium on

Unsteady Aerodynamics, Aeroacoustics & Aeroelasticity of Turbomachinery and

Propellers, September 15-19, 1991, Notre Dame, IN

34- M. H. Dunn and F. Farassat: High Speed Propeller Noise Prediction| A

Multidisciplinary Approach. AIAA Journal, 30(7), July 1992, 1716-1723

35- F. Farassat, M. H. Dunn and P. L. Spence: Advanced Propeller Noise

Prediction in the Time Domain. AIAA Journal (Technical Note), 30(9), 1992,

2337-2340

36- F. Farassat and M. K. Myers: Aeroacoustics of High-Speed Rotating

Blades: The Analytical Aspect, Computational Acoustics | Acoustic Propagation, D. Lee, R. Vichnevetsky and A. R. Robinson, North-Holland Publishing Company, Amsterdam, 1993, 117-148

37- F. Farassat: Introduction to Generalized Functions with Applications in

Aerodynamics and Aeroacoustics. NASA TP-3428, 1994, Corrected Copy

(April 1996)

38- F. Farassat and M. K. Myers: Line Source Singularity in the Wave Equation and Its Removal by Quadrupole Sources | A Supersonic Propeller Noise

Problem. Structural Acoustics, Scattering and Propagation, J. E. Ffowcs Williams,

NASA Technical Memorandum 216178 21
Multidisciplinary Approach. AIAA Journal, 30(7), July 1992, 1716-1723

35- F. Farassat, M. H. Dunn and P. L. Spence: Advanced Propeller Noise

Prediction in the Time Domain. AIAA Journal (Technical Note), 30(9), 1992,

2337-2340

36- F. Farassat and M. K. Myers: Aeroacoustics of High-Speed Rotating

Blades: The Analytical Aspect, Computational Acoustics | Acoustic Propagation, D. Lee, R. Vichnevetsky and A. R. Robinson, North-Holland Publishing Company, Amsterdam, 1993, 117-148

37- F. Farassat: Introduction to Generalized Functions with Applications in

Aerodynamics and Aeroacoustics. NASA TP-3428, 1994, Corrected Copy

(April 1996)

38- F. Farassat and M. K. Myers: Line Source Singularity in the Wave Equation and Its Removal by Quadrupole Sources | A Supersonic Propeller Noise

Problem. Structural Acoustics, Scattering and Propagation, J. E. Ffowcs Williams,

D. Lee, and A. D. Pierce, editors, World Scientific, Singapore, 1994, 29-43

39- F. Farassat and M. K. Myers: The Kirchhoff Formula for a Supersonically Moving Surface, June 12-15, 1995, Munich, Germany, CEAS/AIAA Paper No. 95-062

40- F. Farassat: Generalized Functions and Kirchhoff Formulas, May 6-8, 1996,

State College, PA, AIAA/CEAS Paper No. 96-1705

41- F. Farassat: The Kirchhoff Formulas for Moving Surfaces in

Aeroacoustics- The Subsonic and Supersonic Cases, NASA Technical

Memorandum 110285, 1996

42- F. Farassat and K. S. Brentner: The Acoustic Analogy and the Prediction of

the Noise of Rotating Blades. Theoretical and Computational Fluid Dynamics,

10(1-4), 1998, 155-170

43- F. Farassat, Kenneth S. Brentner and M. H. Dunn: A Study of Supersonic

Surface Sources- The Ffowcs Williams-Hawkings Equation and the Kirchhoff

Formula, AIAA 98-2375

44- Kenneth S. Brentner and F. Farassat: Analytical Comparison of the

Acoustic Analogy and Kirchhoff Formulation for Moving Surfaces, AIAA

Journal, 36(8), 1998, 1379-1386

45- F. Farassat and K. S. Brentner: Supersonic Quadrupole Noise Theory for

High-Speed helicopter Rotors, Journal of Sound and Vibration, 218(3), 1998,

481-500

46- F. Farassat and Mark Farris: The Mean Curvature of the Influence Surface

of Wave Equation With Sources on a Moving Surface, Analytical Methods in

the Applied Sciences, 22, 1999, 1485-1503

22 NASA Technical Memorandum 216178
the Noise of Rotating Blades. Theoretical and Computational Fluid Dynamics,

10(1-4), 1998, 155-170

43- F. Farassat, Kenneth S. Brentner and M. H. Dunn: A Study of Supersonic

Surface Sources- The Ffowcs Williams-Hawkings Equation and the Kirchhoff

Formula, AIAA 98-2375

44- Kenneth S. Brentner and F. Farassat: Analytical Comparison of the

Acoustic Analogy and Kirchhoff Formulation for Moving Surfaces, AIAA

Journal, 36(8), 1998, 1379-1386

45- F. Farassat and K. S. Brentner: Supersonic Quadrupole Noise Theory for

High-Speed helicopter Rotors, Journal of Sound and Vibration, 218(3), 1998,

481-500

46- F. Farassat and Mark Farris: The Mean Curvature of the Influence Surface

of Wave Equation With Sources on a Moving Surface, Analytical Methods in

the Applied Sciences, 22, 1999, 1485-1503

47- F. Farassat: Acoustic Radiation From Rotating Blades - The Kirchhoff

Method in Aeroacoustics, JSV, 239 (4), 2001, 785-800 (Philip Doak 80th Birthday Issue)

48- J. Casper and F. Farassat: Broadband Trailing Edge Noise Predictions in

the Time Domain, Journal of Sound and Vibration, 271(1-2), 2004, 159-176

49- F. Farassat and J. Casper: Some Analytic Results for the Study of

Broadband Noise Radiation from Wings, Propellers and Jets in Uniform Motion,

International Journal of Aeroacoustics, 2(3-4), 2003, 335|350

50- Douglas M. Nark and F. Farassat: CDUCT-LaRC Status - Shear Layer Refraction and Noise Radiation, AIAA-2006-2587, 12th AIAA/CEAS Aeroacoustics

Conference, May 8-10, 2006, Cambridge, Massachusetts

51- F. Farassat, Jay H. Casper, Ana F. Tinetti and M. H. Dunn: Airframe Noise

Prediction by Acoustic Analogy:

Revisited, AIAA-2006-2564, 12th AIAA/CEAS Aeroacoustics Conference, May

8-10, 2006, Cambridge, Massachusetts

52- F. Farassat: Derivation of Formulations 1 and 1A of Farassat, NASATM-2007-214853, March 2007

53- Handbook Article- F. Bruce Metzger and F. Farassat, Aircraft Propeller

Noise Sources, Prediction, and Control, Chapter 87 of Handbook of Noise and

Vibration Control (Malcolm Crocker, Editor), John Wiley and Sons, 2007

54- Seongkyu Lee, Kenneth S. Brentner, F. Farassat and Philip J. Morris: Analytic

Formulation and Numerical Implementation of an Acoustic Pressure

Gradient Prediction, Journal of Sound and Vibration 319, 2009, 1200|1221 

NASA Technical Memorandum 216178 23
tion and Noise Radiation, AIAA-2006-2587, 12th AIAA/CEAS Aeroacoustics

Conference, May 8-10, 2006, Cambridge, Massachusetts

51- F. Farassat, Jay H. Casper, Ana F. Tinetti and M. H. Dunn: Airframe Noise

Prediction by Acoustic Analogy:

Revisited, AIAA-2006-2564, 12th AIAA/CEAS Aeroacoustics Conference, May

8-10, 2006, Cambridge, Massachusetts

52- F. Farassat: Derivation of Formulations 1 and 1A of Farassat, NASATM-2007-214853, March 2007

53- Handbook Article- F. Bruce Metzger and F. Farassat, Aircraft Propeller

Noise Sources, Prediction, and Control, Chapter 87 of Handbook of Noise and

Vibration Control (Malcolm Crocker, Editor), John Wiley and Sons, 2007

54- Seongkyu Lee, Kenneth S. Brentner, F. Farassat and Philip J. Morris: Analytic

Formulation and Numerical Implementation of an Acoustic Pressure

Gradient Prediction, Journal of Sound and Vibration 319, 2009, 1200|1221 

ü 4.2- Supplementary [S] References

S1- F. Bruce Metzger: A Review of Propeller Noise PredictionMethodology

1919-1994, NASA Contractor Report 198156, June 1995

S2- M. J. Lighthill: On sound generated aerodynamically I. General

theory. Proceedings of the Royal Society, A211, 1952, 564-587

S3- J. E. Ffowcs Williams and D. L. Hawkings: Sound Generation by Turbulence

and Surfaces in Arbitrary Motion, Philosophical Transactions of the Royal Society,

A264, 1969, 321-342

S4- Kenneth S. Brentner, Prediction of Helicopter Discrete Frequency Rotor NoiseA Computer Program Incorporating Realistic Blade Motions and Advanced Formulation, October 1986, NASA TM 87721

S5- M. H. Dunn and G. M. Tarkenton: Computational Methods in the Prediction of

Advanced Subsonic and Supersonic Propeller Induced Noise| ASSPIN Users'

Manual, NASA Contractor Report 4434, April 1992

S6- Donald B. Hanson: Direct Frequency Domain Calculation of Open Rotor

Noise, AIAA Journal (Technical Note), 30(9), 1992, 2334-2337

S7- Mark H. Dunn and Ana F. Tinetti: Aeroacoustic Scattering Via The Equivalent

Source Method, AIAA 2004-2937, 10th AIAA/CEAS Aeroacoustics Conference,

May 10 - 12, 2004, Manchester, England 

S8- Ana F. Tinetti, Mark H. Dunn and D. Stewart Pope: Fast Scattering Code

(FSC) Userʼs Manual- Version 2.0, NASA/CR-2006-214510, October 2006

S9- Carl H. Gerhold, Lorenzo R. Clark, Mark H. Dunn and John Tweed: Investigation of acoustical shielding by a wedge-shaped airframe, Journal of Sound and

Vibration, 294, 2006, 49|63

24 NASA Technical Memorandum 216178
S9- Carl H. Gerhold, Lorenzo R. Clark, Mark H. Dunn and John Tweed: Investigation of acoustical shielding by a wedge-shaped airframe, Journal of Sound and

Vibration, 294, 2006, 49|63

S10- Mark H. Dunn and Ana F. Tinetti: Application of Fast Multipole Methods to

the NASA Fast Scattering Code, 14th AIAA/CEAS Aeroacoustics Conference, May

5-7, 2008, Vancouver, British Columbia, Canada

NASA Technical Memorandum 216178 25
REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

2. REPORT TYPE 

Technical Memorandum

 4. TITLE AND SUBTITLE

Open Rotor Noise Prediction at NASA Langley - Capabilities, Research 

and Development

5a. CONTRACT NUMBER

 6. AUTHOR(S)

Farassat, F.

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

NASA Langley Research Center

Hampton, VA 23681-2199

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

National Aeronautics and Space Administration

Washington, DC 20546-0001

 8. PERFORMING ORGANIZATION

 REPORT NUMBER

L-19770

10. SPONSOR/MONITOR'S ACRONYM(S)

NASA

13. SUPPLEMENTARY NOTES

12. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified - Unlimited

Subject Category 71

Availability: NASA CASI (443) 757-5802

19a. NAME OF RESPONSIBLE PERSON

STI Help Desk (email: help@sti.nasa.gov)

14. ABSTRACT

The high fuel prices of recent years have caused the operating cost of the airlines to soar. In an effort to bring down the fuel consumption, the major aircraft 

engine manufacturers are now taking a fresh look at open rotors for the propulsion of future airliners. Open rotors, also known as propfans or unducted fans, 

can offer up to 30 per cent improvement in efficiency compared to high bypass engines of 1980 vintage currently in use in most civilian aircraft. NASA 

Langley researchers have contributed significantly to the development of aeroacoustic technology of open rotors. This report discusses the current noise 

prediction technology at Langley and reviews the input data requirements, strengths and limitations of each method as well as the associated problems in need 

of attention by the researchers. We present a brief history of research on the aeroacoustics of rotating blade machinery at Langley Research Center. We then 

discuss the available noise prediction codes for open rotors developed at NASA Langley and their capabilities. In particular, we present the two useful 

formulations used for the computation of noise from subsonic and supersonic surfaces. Here we discuss the open rotor noise prediction codes ASSPIN and one 

based on Ffowcs Williams-Hawkings equation with penetrable data surface (FW - Hpds). The scattering of sound from surfaces near the rotor are calculated 

using the fast scattering code (FSC) which is also discussed in this report. Plans for further improvements of these codes are given. 

15. SUBJECT TERMS

Aeroacoustics; Aircraft noise prediction; Open rotors; Propfans; Ffowcs Williams-Hawkings equation; Time domain method; 

Fast Scattering Code (FSC); Multidimensional generalized functions

18. NUMBER

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30

19b. TELEPHONE NUMBER (Include area code)

(443) 757-5802

a. REPORT

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c. THIS PAGE

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b. ABSTRACT

U

17. LIMITATION OF 

 ABSTRACT

UU

Prescribed by ANSI Std. Z39.18

Standard Form 298 (Rev. 8-98)

3. DATES COVERED (From - To)

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

561581.02.08.07.18.03

11. SPONSOR/MONITOR'S REPORT

 NUMBER(S)

NASA/TM-2010-216178

16. SECURITY CLASSIFICATION OF:

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 this 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)

01- 01 - 2010