Helicopter rotor Blade Wake Interaction (BWI) noise is known to be significant during take-off and level flight. Less attention has been given to descent flight conditions, where Blade Vortex Interaction (BVI) noise is dominant. The present study investigates BWI noise in descent flight conditions by analyzing the HELISHAPE descent case database. Through signal analysis of both acoustic waveforms and spectra, the rotor azimuthal region responsible for BWI noise is localized and the dominance of BVI noise in the BWI frequency region is shown. Coherence analysis of the blade pressure data indicate significant chordwise coherence in the 3 to 4 Strouhal number range and absence of acoustic dipoles in the BWI frequency range. Comparison with analysis of a swept-back blade-tip database showed that blade-tip shape does not affect BWI noise. The findings of this study support BWI prediction models based on Amiet's theory and suggest that BWI noise can be ignored for predictions of rotor noise in descent flight conditions.
SchmitzF. H., Rotor noise, NASA Ames Research Center, Moffett Field, California, 1991.
3.
BrooksT. F.JollyJ. R. and MarcolliniM. A., Helicopter Main Rotor Noise: Determination of Source Contributions using Scaled Model Data, NASA Technical Paper 2825, August 1988.
4.
BrooksT. F.MarcoliniM. A., and PopeD. S., Main Rotor Broadband Noise Study in the DNW, Journal of the AHS, Vol. 34(2), 1989, pp. 3–12.
5.
GleggS. A. L., Prediction of Blade Wake Interaction Noise Based on a Turbulent Vortex Model, AIAA Journal, Vol. 29 (10), 1991.
6.
AmietR. K., Acoustic Radiation from an Airfoil in a Turbulent Stream, Journal of Sound and Vibration, Vol. 41 (4), pp. 407–420, 1975.
7.
WittmerK. S.DevenportW. J. and GleggS. A. L., Perpendicular Blade Vortex Interaction, AIAA Journal, Sept 1995, pp. 1667–1674.
8.
GleggS. A. L.WitmmerK. S.DevenportW. J. and PopeD. S., Broadband Helicopter Noise, AHS Specialists' Meeting for Rotorcraft Acoustics and Aerodynamics, Williamsburg, Virginia, Oct 1997.
9.
BrooksT. F.BurleyC. L., Blade Wake Interaction Noise for a Main Rotor, Journal of the AHS, 49(1), 2004, pp. 11–27.
10.
BurleyC. L.BrooksT. F.SplettstoesserW. R.SchultzK.-J.KubeR.BucholtzH.WagnerW., and WeitmeyerW., Blade Wake Interaction Noise for a BO-105 Model Main Rotor, AHS Technical Specialists' Meeting for Rotorcraft Acoustics and Aerodynamics, Williamsburg, VA, Oct 1997.
11.
SplettstoesserW. R.CubeR.WagnerW.SeelhorstU.BoutierA.MicheliF.MerckerE. and PengelK., Key results from a Higher Harmonic Control Aeroacoustic Rotor Test (HART), Journal of the AHS, 1997, 42(1).
12.
BrooksT. F., and BurleyC. L., Rotor Broadband Noise prediction with Comparison to Model Data, AIAA Paper No. 2001–2210, 2001.
13.
BurleyC. L., and BrooksT. F., Rotor Broadband Noise prediction with Comparison to Model Data, Journal of the AHS, 49(1), 2004.
14.
BrezillionJ.PrieurJ. and RahierJ., Investigation on Broadband Helicopter Noise, AHS Rotorcraft Acoustics and Aerodynamics Specialists Meeting, Williamsburg, Virginia, Oct 1997.
15.
BouchetE. and RahierG., Structure of the Blade Pressure Fluctuations Generated by Helicopter Rotor Blade-Wake Interaction, 56th AHS Annual Forum, Virginia Beach, Virginia, May 2000.
16.
DevenportW. J.VogelC. M. and ZsoldosJ. S., Flow structure produced by the interaction and merger of a pair of co-rotating wing-tip vortices, J. Fluid Mech, Vol 394, pp. 357–377, 1999.
17.
MauffreyY.RahierG. and PrieurJ., Numerical Investigation on Blade/Wake-Interaction Noise Generation, Journal of Aircraft, Vol. 46, No. 5, 2009.
18.
Le DizesS., and LaporteF., Theoritical predictions for the elliptical instability in a two-vortex flow, J. Fluid Mech., Vol. 471, pp. 169–201, 2002.
19.
MeunierP., and LewekeT., Elliptic Instability of a Co-rotating Vortex Pair, J. Fluid Mech., Vol. 533, pp. 125–159, 2005.
20.
SchultzK. J.SplettstoesserW.JunkerB. and WagnerW., A parametric windtunnel test on rotorcraft aerodynamics and aeroacoustics (HELISHAPE) – test procedures and representative results, 22nd European Rotorcraft Forum, Brighton, UK, 1996.
21.
SchneiderO. and Van der WallB.G., Comparison of Simple and Conditional Averaging Methodology Based on Results of the HART II Wind Tunnel Test, International Forum on Rotorcraft Multidisciplinary Technology, Seoul, Korea, (2007).
22.
BrooksT. F., Effect of signal jitter on the spectrum of impulsive noise, NASA Technical Memorandum 100–477, June 1987.
23.
SplettsoesserW. R.SchultzK. J. and MartinR. M., Rotor Blade-Vortex Interaction Impulsive noise Source localization, AIAA Journal, Vol. 28, 593–600, April 1990.
24.
MarcoliniM. A. and BrooksT. F., Rotor Noise Measurement Using a Directional Microphone Array, AIAA Paper 87–2746, 1987.
25.
MartinR. M. and HardinJ. C., “Spectral Characteristics of Rotor Blade/Vortex Interaction Noise”, J. Aircraft, Vol. 25, No. 1, 1987.
26.
MenounouP. and VitsasP. A., Numerical investigation of nonlinear propagation distortion effects in helicopter rotor noise, J. Acoust. Soc. Am., Vol. 126, Issue 4, pp. 1690–1699 (October 2009).
27.
EgolfT. A. and LandgrebeA. J., Helicopter Rotor Wake Geometry and its Influence in Forward Flight, Volume II – Wake Geometry Charts, NASA CR 3727, 1983.
28.
DritschelD. G., and WaughD. W., Quantification of the inelastic interaction of unequal vortices in two-dimensional vortex dynamics, Phys. Fluids, Vol. 4, 1992.
29.
TrielingR. R.FuentesVelasco O. U., and van HeijstG. J. F., Interaction of two unequal co-rotaring vortices, Phys. Fluids, Vol. 17, 2005.
30.
GovindarajuS. P., and SaffmanP. G., Flow in a Turbulent Trailing Vortex, Phys. Fluids, Vol. 14(10), 1971.
