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1 Slide 1

For STAR South East Asian Conference 2015

Prediction of noise emission from the NASA SR-2 Propeller

8-9 June 2015 Mr Voo Keng Soon Mr Tan Chun Hern

Mr Lim Nee Sheng Winson Dr Siauw Wei Long



2 Slide 2

A big thank you to CD-adapco for the provision of technical assistance and advice!

Dr Mark Farrall Dr Fred Mendonça

Dr Amel Boudjir Dr Jason Fernandes



3 Slide 3

Motivation •  Fundamental study of noise emission from flow over propeller •  Comparison of the usage of acoustics analogy and direct

measurement method for computational aeroacoustics •  Investigate the appropriate usage of Moving Reference Frame

and Rigid Body Motion (sliding mesh) methodologies in the modelling of the propeller

•  Study the behaviour of the propeller tip vortices in the presence of a generic wing

•  NASA SR-2 propeller selected as validation case due to the availability of open source data



4 Slide 4

Overview •  Propeller Basics •  Simulation Methodology •  Generation of SR-2 propeller CAD •  Differences between CFD Setups •  CFD Setup of SR-2 propeller •  SR-2: Analysis •  Propeller in the Presence of Generic Wing •  SR-2 + NACA0010: Analysis •  Summary



5 Slide 5

Propeller Basics •  [1] held measured noise level and corresponding

spectral representations on a Cessna 172N (two-blade propeller) while [2] tested the Cessna FR172F (three-blade propeller)

•  At high propeller RPM, noise at the blade passing frequency (BPF) is the dominant noise

2400rpm, 80Hz, 93.3dB

2400rpm, 120Hz, 91dB

[1] D.Miljkovic, M.Maletic, M.Obad, 2007. “Comparative Investigation of Aircraft Interior Noise Properties”, 3rd Congress of the Alps-Adria Acoustics Association. [2] D.Miljkovic, J. Ivosevic, T.Bucak, 2012. “Two vs Three Blade Propeller – Cockpit Noise Comparison”, 5th Congress of the Alps-Adria Acoustics Association.



6 Slide 6

Propeller Basics



7 Slide 7

[3] J.E. Marte, D.w. Kurtz, 1970. “A Review of Aerodynamic Noise From Propellers, Rotors, and Lift Fans”, NASA CR107568. [4] E.L. Chuan-Tau, J. Roskam, 2008. “Airplane Aerodynamics and Performance”, DARcorporation, USA.

http://static.thisdayinaviation.com

Propeller Basics



8 Slide 8

http://www.aircav.com

https://www.nas.nasa.gov/SC12/demos/demo1.html


Propeller Basics



9 Slide 9


Propeller Basics



10 Slide 10

Propeller Basics

va

D



11 Slide 11

Propeller Basics[4][5]

[4] E.L. Chuan-Tau, J. Roskam, 2008. “Airplane Aerodynamics and Performance”, DARcorporation, USA. [5] F.E. Weick, 1930. “Aircraft Propeller Design”, McGraw-Hill Book Company, USA



12 Slide 12

Simulation Methodology

The following was employed for this aeroacoustics study of the NASA SR-2 propeller 1. Generation of propeller geometry, followed by meshing within the domain 2. Upon completion of volume meshing, simulation is setup to run steady state with Moving Reference Frame (MRF) 3. Converged steady solution is then used to calculate the propeller power coefficient, Cp

4. Calibration of blade angle through a series of steady state simulations at varied propeller blade angle, so as to match the predicted Cp to the experimental Cp

5. Upon calibration of the propeller blade angle, the simulation is then setup to run transiently with rigid body motion (sliding mesh) 6. The transient simulation is allowed to run for at least 10 propeller rotations to transit to a “steady” condition 7. Simulation is subsequently ran for a further 10 propeller rotations in order to record the pressure signal at the receivers 8. Pressure data recorded at the receivers processed to acquire sound pressure levels at the blade passing frequency (BPF)



13 Slide 13

Simulation Methodology

The following was employed for the physics modelling • Time step of 2.5e-5 seconds utilized to capture propeller rotation rate of 1° per time-step • 10 inner iterations for convergence of time-step

Steady State Simulation Transient Simulation Steady Implicit unsteady

Segregated flow Segregated flow

Ideal gas Ideal gas

Segregated fluid enthalpy Segregated fluid enthalpy

K-Ω SST Detached Eddy Simulation (K-Ω based)

All Y+ wall treatment All Y+ wall treatment

Cell quality remediation Cell quality remediation



14 Slide 14

Generation of SR-2 propeller CAD[6]

[6] G.L.Stefko, R.J.Jeracki, 1985. “Wind Tunnel Results of Advanced High Speed Propellers in Takeoff, Climb & Landing Operating Regimes”, AIAA-85-1259.



15 Slide 15

Generation of SR-2 propeller CAD

Root portion (r/R from 0.239 to 0.367) of propeller utilized modified NACA 65 series airfoil profiles having a circular arc mean camber line[7][8]

NACA 16 se r ies a i r fo i l profiles[4] are utilized at the outer portion (r/R from 0.449 to 1.0) of the propeller.

r/R t/b Corrected b/D Corrected CLD Corrected delta β Corrected β

0.239 0.19804 0.14485 -‐0.23259 23.325 82.3250.250 0.16342 0.14521 -‐0.18897 22.585 81.5850.275 0.12503 0.14557 -‐0.10860 20.851 79.8510.300 0.10005 0.14629 -‐0.03922 18.979 77.9790.325 0.08589 0.14702 0.00820 17.219 76.2190.350 0.07471 0.14774 0.04465 15.465 74.4650.367 0.06898 0.14810 0.06392 14.355 73.3550.449 0.05097 0.14990 0.12993 10.098 69.0980.5 0.04377 0.15061 0.15401 8.185 67.1850.55 0.03762 0.15058 0.16679 6.394 65.3940.6 0.03279 0.14981 0.16665 4.726 63.7260.65 0.02907 0.14831 0.16096 3.058 62.0580.7 0.02625 0.14680 0.14789 1.483 60.4830.75 0.02364 0.14529 0.12190 0.000 59.0000.8 0.02234 0.14268 0.10144 -‐1.405 57.5950.85 0.02083 0.13764 0.07729 -‐3.243 55.7570.9 0.02080 0.12896 0.05195 -‐5.188 53.8120.95 0.02040 0.11304 0.02530 -‐6.394 52.6060.96 0.02003 0.10789 0.01973 -‐6.600 52.4000.97 0.02002 0.10051 0.01417 -‐6.765 52.2350.98 0.02002 0.09201 0.00860 -‐6.935 52.0650.99 0.02001 0.07792 0.00303 -‐7.044 51.9561 0.02000 0.05824 -‐0.00582 -‐7.083 51.917

[4] E.L. Chuan-Tau, J. Roskam, 2008. “Airplane Aerodynamics and Performance”, DARcorporation, USA. [7] N.A. Cumpsty, 1989. “Compressor Aerodynamics”, Longman Scientific & Technical, USA [8] D.C. Mikkelson, B.J. Blaha, G.A. Mitchell, J.E. Wikete, 1977. “Design and Performance of Energy Efficient Propellers for Mach 0.8 Cruise”, NASA TM X-73612.



16 Slide 16


Fine tuning of digitalized data a) Blade thickness ratio, t/b was fine-tuned, knowing t/b at tip is 2%[8]

b) Blade width ratio, b/D was fine-tuned, knowing blade activity factor AF=203[8][9]

c) Blade design lift coefficient, CLD was fine-tuned, knowing integrated design lift coefficient CLI = 0.081[8][9]

d) Change in blade angle with respect to that at 75% blade radius, Δβ was fine-tuned, knowing Δβ=0 at 0.75 r/R[8][9]

[8] D.C. Mikkelson, B.J. Blaha, G.A. Mitchell, J.E. Wikete, 1977. “Design and Performance of Energy Efficient Propellers for Mach 0.8 Cruise”, NASA TM X-73612. [9] G.L. Stefko, R.J. Jeracki, 1985. “Wind-Tunnel Results of Advanced High-Speed Propellers at Takeoff, Climb, and Landing Mach Numbers”, NASA TM 87030.


[9] G.L. Stefko, R.J. Jeracki, 1985. “Wind-Tunnel Results of Advanced High-Speed Propellers at Takeoff, Climb, and Landing Mach Numbers”, NASA TM 87030.

•  Geometry generation of area-ruled spinner and turbine sting[9]

•  The area-ruled spinner and turbine sting were designed to alleviate blade-root choking and to minimize compressibility drag rise.

turbine sting

•  The generated propeller blades fitted nicely with the spinner •  Inboard portion of propeller operates as a cascade rather than isolated blades


•  Differences between earlier and current aeroacoustics studies of the NASA SR-2 propeller •  Improved CAD modelling of the propeller blades[4][7][8][9][10] •  Obtaining geometry data of spinner and turbine sting[9]

•  Revised simulation conditions with inference from new literature[11][12]

•  Inclusion of the acoustic plate in the modelling[13]

Differences between CFD Setups

current setup

[10] T.A. Egolf, O.A. Anderson, D.E. Edwards, A.J. Landgrebe, 1988. “An Analysis for High Speed Propeller-Nacelle Aerodynamic Performance Prediction”, NASA-CR-4199. [11] J.H. Dittmar, and P.L. Lasagna, 1982. “A Preliminary Comparison Between the SR-3 Propeller Noise in Flight and in a Wind Tunnel”, NASA-TM-82805. [12] J.H. Dittmar, R.J. Jeracki, and B.J. Blaha, 1979. “Tone Noise of Three Supersonic Helical Tip Speed Propellers in a Wind Tunnel”, NASA-TM-79167. [13] J.H. Dittmar, R.J. Burns, D.J. Leciejewski, 1984. “An Experimental Investigation of the Effect of Boundary Layer Refraction on the Noise From a High-Speed Propeller”, NASA TM 83764.

previous setup



21 Slide 21

CFD Setup of SR-2 propeller

[13] J.H. Dittmar, R.J. Burns, D.J. Leciejewski, 1984. “An Experimental Investigation of the Effect of Boundary Layer Refraction on the Noise From a High-Speed Propeller”, NASA TM 83764.

•  Modelled geometry of plate (holding the installed pressure transducers)[13]

•  Patches of 16mm diameter were imprinted on the base of the CAD geometry of the plate to represent the pressure probe points

[13] J.H. Dittmar, R.J. Burns, D.J. Leciejewski, 1984. “An Experimental Investigation of the Effect of Boundary Layer Refraction on the Noise From a High-Speed Propeller”, NASA TM 83764.

CFD Setup of SR-2 propeller



23 Slide 23

CFD Setup of SR-2 propeller •  Trimmed hexahedral mesh

with prism layers •  97.3 million cells •  Wall Y+ < 1 at critical areas •  Unknown mass flow exiting

from rear of air turbine sting •  Tangent ogive cylinder added

to the rear to minimize undesirable noise generation due to abrupt flow separation

(section cut @ Y=0)

[11] J.H. Dittmar, and P.L. Lasagna, 1982. “A Preliminary Comparison Between the SR-3 Propeller Noise in Flight and in a Wind Tunnel”, NASA-TM-82805. [12] J.H. Dittmar, R.J. Jeracki, and B.J. Blaha, 1979. “Tone Noise of Three Supersonic Helical Tip Speed Propellers in a Wind Tunnel”, NASA-TM-79167. [13] J.H. Dittmar, R.J. Burns, D.J. Leciejewski, 1984. “An Experimental Investigation of the Effect of Boundary Layer Refraction on the Noise From a High-Speed Propeller”, NASA TM 83764. [14] J.H. Dittmar, 1989. “Cruise Noise of the SR-2 Propeller Model in a Wind Tunnel”, NASA-TM-101480.

Fixed Conditions SetupPropeller diameter (m) 0.6223Cruise Mach 0.6

Environmental ConditionsPressure, P (Pa) 90110Temperature, T (K) 279speed of sound (m/s) corresponding to above P & T 334.85air density (kg/m3) corresponding to above P & T 1.1251

Propeller ConditionsPropeller rotation rate (RPM) 6330.5Propeller rotation speed (m/s) 206.27propeller helical tip speed (m/s) 287.94propeller helical Mach 0.860advance ratio, J 3.060

Simulation OutputPropeller Torque, Q (Nm) 244.63P, shaft power (W) 162174.41Power Coefficient Cp 1.32

from literature [8][9][10][11][12][13]

Inferred from literature [11][12]

Matched literature [14]

Delta blade angle of -0.4° utilized to match experimental Cp of 1.32 [14]

US Standard Atmosphere 1976

SR-2 : Analysis



25 Slide 25

suction side suction side

pressure side pressure side

SR-2 : Analysis



26 Slide 26

smaller peak to peak amplitude

[15] J.H. Dittmar, R.J. Jeracki, and B.J. Blaha, 1979. “Tone Noise of Three Supersonic Helical Tip Speed Propellers in a Wind Tunnel”, NASA-TM-79167.

Pressure-time trace (probe on tunnel wall) •  Sinusoidal waveform observed in CFD •  Sinusoidal waveform observed in wind

tunnel data (SR-2, M0.6, J3.06)[15]

•  Steep fronted wave (approaches classic N wave shock pattern) observed in wind tunnel data (SR-2, M0.8, J3.07)[15]

•  The latter is a good indication on the presence of sharp pressure rises normally associated with supersonic helical tip speed

Helical tip mach 0.857 Helical tip mach 1.14

SR-2 : Analysis



27 Slide 27

Comparison with previous setup (using direct measurement)

current setup previous setup

•  With the updated geometries, the current setup exhibited a closer match in the sound pressure level @BPF when compared to the experimental data

•  A delta of 1.173 dB at probe 6 (@ X=0.3in) as compared to experimental data

•  Pre-processing is important! Whenever possible, usage of b e t t e r g e o m e t r y C A D representation will lead to peace of mind

SR-2 : Analysis



28 Slide 28

Comparison with previous setup (using FW-H Impermeable) •  Measurement locations are too close to

source, noise does not necessarily meet farfield conditions[11]

•  Ffowcs Williams-Hawkings (FW-H) method is a form of acoustic analogy applied to reduce aeroacoustics sound sources to simple emitter type

•  Such methods rely on near-field information gathered over surface(s) enclosing as much as possible the noise sources

•  These methods propagate noise from source to receiver via analytical solution of the wave equation

•  In the far field, sound behaves as in open air without reflecting surfaces to interfere with its propagation

•  The near field is the area very close to the noise source where the sound pressure level may vary significantly with a small change in position

•  Advantage of FW-H: Only require CFD solution around source, not expensive

•  Disadvantage of FW-H: Cannot account for reflection[16]

•  Acoustic analogy not recommended for this CFD setup [11] J.H. Dittmar, and P.L. Lasagna, 1982. “A Preliminary Comparison Between the SR-3 Propeller Noise in Flight and in a Wind Tunnel”, NASA-TM-82805. [16] A. Zinoviev, 2002. “Application of Ffowcs Williams and Hawkings Equation to Sound Radiation by Vibrating Solid Objects in a Viscous Fluid: Inconsistencies and the Correct Solution”, ISBN 0-909882-19-3@2002 AAS

Near Field acoustic receiver

FW-H (solve wave equation)

CFD (solve Navier-Stokes)

Far Field

Noise Sources

SR-2 : Analysis



29 Slide 29

+ ≈Propeller generates noise Airfoil generates noise Propeller + Airfoil = …

more noise???

http://www.apkxda.com http://7-themes.com http://www.metalimpact.com

Propeller in the Presence of Generic Wing



30 Slide 30

SR-2 + NACA0010 : Analysis

Comparison with and without NACA10 wing (using direct measurement)

SR-2 SR-2 + NACA10

Addition of NACA10 wing •  Slightly reduced dB at probe 5-6 •  Reduced dB from probe 3 to 11 •  Increased dB at Probe 1,2, 12 Propeller + Airfoil = …

less noise?!?

perhaps only at the BPF???

drop of 0.66dB



31 Slide 31

Addition of NACA10 wing •  Slightly reduced dB at probe 5-6 •  Reduced dB from probe 3 to 11 •  Increased dB at Probe 1,2, 12

Comparison with and without NACA10 wing (using direct measurement)

Propeller + Airfoil = … generally lesser noise at probes near to propeller!

why???


SR-2 SR-2 + NACA10



32 Slide 32 [17] L.L.M. Veldhuis, 2005. “Propeller Wing Aerodynamic Interference”, Delft University of Technology.

Pressure coefficient contour plots •  Sections of blades coloured blue shows area of suction •  Areas coloured red shows high pressure stagnation •  Presence of wing causes significant reduction in rotation (swirl velocity)[17]

•  Viewing from front, the propeller is rotating clockwise •  Viewing from front, wing to the left of propeller experienced positive local

angle of angle, leading to higher lift force •  Viewing from front, wing to the right of propeller experienced negative

local angle of attack, leading to lower lift force




33 Slide 33

SR-2

SR-2 + NACA10 http://www.aip.org




34 Slide 34

SR-2

SR-2 + NACA10

http://www.flickr.com

[18] M.M. Hand, 2001. “Unsteady Aerodynamics Experiment Phase VI: Wind Tunnel Test Configurations and Available Data Campaigns”, NREL/TP-500-29955.

http://www.flickr.com




35 Slide 35


[19] R.T. Johnston, J.P. Sullivan, 1993. “Unsteady Wing Surface Pressures in the Wake of a Propeller”, Journal of Aircraft Vol. 30, No. 5. [20] A.D. Thom, 2011. “Analysis of Vortex-Lifting Surface Interactions”, University of Glasgow.



36 Slide 36


[19] R.T. Johnston, J.P. Sullivan, 1993. “Unsteady Wing Surface Pressures in the Wake of a Propeller”, Journal of Aircraft Vol. 30, No. 5. [20] A.D. Thom, 2011. “Analysis of Vortex-Lifting Surface Interactions”, University of Glasgow.

Y = -R

Y = -R -2cm

Y = -R +2cm

•  Local deformation of propeller tip vortex at wing leading edge[19][20]

•  As vortex approaches wing, it will be displaced outwards from the turbine sting

Outwards spanwise flow

Inwards spanwise flow

•  Bending around the leading edge, vortex moves inwards towards sting

•  Vortex leaves trailing edge at different span locations and time, resulting in shearing of propeller wake



37 Slide 37

[21] S.Oerlemans, P.Sijtsma, B.M. López, 2007. “Location and quantification of noise sources on a wind turbine”, Journal of Sound and Vibration 299.

•  Acoustic field measurements carried out in the framework of the European SIROCCO project found that all the array results reveal that besides a minor source at the rotor hub, practically all noise (emitted to the ground) is produced during the downward movement of the blades[21]




38 Slide 38

•  Acoustic plate located above propeller •  propeller rotating clockwise (view from

front) •  Upward stroke of propeller blades at region

left of spinner (view from front) liable for noise detected by probes on acoustic plate

•  Proximity of airfoil wing to the propeller plane affecting the air flow in the vicinity of the propeller

•  Presence of wing near the propeller may have shielded some of the propeller acoustic effect recorded on probe 4 to 11

•  Probe 12, located further down the airfoil chord, detected a higher noise

•  Perhaps a higher noise contribution from airfoil further downstream of Probe 12?

•  Literature review on the aeroacoustics impact of tractor configuration with varied test conditions returned ambiguous findings[22][23]


[22] P.J.W. Block, 1986. “Experimental Study of the Effects of Installation on single- and Counter- Rotation Propeller Noise”, NASA-TP-2541. [23] R.P. Woodward, 1987. “Measured Noise of a Scale Model High Speed Propeller at Simulated Takeoff/Approach Conditions”, NASA-TM-88920.



39 Slide 39

Summary •  Aeroacoustics simulation of the SR-2 with updated geometries detected noise at a closer fit

to the experimental data, registering a difference of 1.173dB at probe 6 •  One has to recognize that pre-processing is of utmost importance, especially if one intends

to invest in DES or LES •  Whenever possible, usage of better geometry CAD representation is recommended •  Appropriate modelling of propeller with MRF or rigid body motion (sliding mesh) is vital •  Direct measurement of probe points and acoustic analogy serve different purposes •  Direct measurement for near field probe points are highly recommended if the probe points

are located within the simulation domain •  Acoustic analogy is an effective method to reduce aeroacoustics sound sources to simple

emitter type for detection in the far field •  Noise (emitted to ground) is produced during downward stroke of propeller blades[21] •  DES simulation of a generic wing aft of the SR-2 propeller at Mach 0.6 had reduced the

noise level recorded on most of the probe points in the near field •  Literature review on the aeroacoustics impact of tractor configuration with varied test

conditions returned ambiguous findings[22][23]

•  Scientific research findings can be vague at times •  One has to keep an open mind and continue one’s research



40 Slide 40

Thank you

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