High-Speed Helicopter Rotor Noise-Shock Waves as a Potent Source of Sound
In this paper we discuss the problem of high speed rotor noise prediction. In particular, we propose that from the point of view of the acoustic analogy, shocks around rotating blades are sources of sound. We show that, although for a wing at uniform steady rectilinear motion with shocks the volume quadrupole and shock sources cancel in the far field to the order of 1/r, this cannot happen for rotating blades. In this case, some cancellation between volume quadrupoles and shock sources occurs, yet the remaining shock noise contribution is still potent. A formula for shock noise prediction is presented based on mapping the deformable shock surface to a time independent region. The resulting equation is similar to Formulation lA of Langley. Shock noise prediction for a hovering model rotor for which experimental noise data exist is presented. The comparison of measured and predicted acoustic data shows good agreement.
KeywordsDura Acoustics Line Source
Unable to display preview. Download preview PDF.
- 1.F. Farassat and K. S. Brentner, “The Uses and Abuses of the Acoustic Analogy in Helicopter Rotor Noise Prediction”, Journal of the AHS, 33 (1), 1988, pp 29–36.Google Scholar
- 2.F. Farassat, “Quadrupole Source in Prediction of the Noise of Rotating Blades - A New Source Description”, AIAA-87–2675, 1987.Google Scholar
- 3.F. Farassat and M. K. Myers, “An Analysis of the Quad rupole Noise of High Speed Rotating Blades”, Computational Acoustics, Vol. 2, D. Lee, A. Cakmak, and R. Vichnevetsky ( Eds. ), Elsevier Science Publishers, 1990, pp 227–240.Google Scholar
- 5.F. Farassat and K. S. Brentner, “The Influence of Quad rupole Sources in the Boundary Layer and Wake of a Blade on Helicopter Rotor Noise”, paper presented at the International Technical Specialists Meeting on Rotorcraft Acoustics and Rotor Fluid Dynamics, sponsored by AHS and RAeS, October 15–17, 1991 Philadelphia, PA.Google Scholar
- 7.R. P. Kanwal, Generalized Functions - Theory and Technique, Academic Press, 1983.Google Scholar
- 8.F. Farassat and H. Tadghighi, “Can Shock Waves on Helicopter Rotors Generate Noise? A Study of the Quadrupole Source”, paper presented at the 46th Annual Forum and Technology Display of the AHS, May, 1990, Washington D.C.Google Scholar
- 10.F. H. Schmitz and Y. H. Yu, “Theoretical Modeling of High Speed Impulsive Noise”, Journal of the AHS, 24 (1), 1979, 10–19.Google Scholar
- 11.K. J. Schultz and W. R. Splettstoesser, “Prediction of Helicopter Rotor Impulsive Noise Using Measured Blade Pressures”, paper presented at the 43rd Annual Forum and Technology Display of the AHS, May 1987, St. Louis, MO.Google Scholar
- 12.F. Farassat, “Theoretical Analysis of Linearized Acoustics and Aerodynamics of Advanced Supersonic Propellers”, AGARD CP- 366, 1984, Aerodynamics and Acoustics of Propellers.Google Scholar
- 13.K. S. Brentner, “Prediction of Helicopter Rotor Discrete Frequency Noise - A Computer Program Incorporating Realistic Blade Motions and Advanced Acoustic Formulation”, NASA TM-87721, 1986.Google Scholar
- 14.H. Tadghighi, R. Holz, F. Farassat and Y.-J. Lee, “Development of a Shock Noise Prediction Code for High-Speed Helicopters - The Sub-sonically Moving Shock”, paper presented at the 47th Annual Forum and Technology Display of the AHS, May 1991, Phoenix, Arizona.Google Scholar
- 16.L. N. Sankar and D. Prichard, “Solution of Transonic Flow Past Rotor Blades Using Conservative Full Potential Equation”, AIAA-85–5012, 1985.Google Scholar