Flyover Helicopter Acoustic Simulation and Correlation

The objective of this paper is to predict rotor impulsive noise using various prediction methodologies available for within WOPWOP3, and correlate predictions with flight test measurements. WOPWOP3 is a computational aeroacoustic program based on the solution to the Ffowcs Williams - Hawkings (FW-H) equation for noise predictions. Noise reduction by design could provide the most effective and cost saving solution. An integrated rotorcraft rotor simulation and analysis tool is required to develop a validated simulation process, which includes both rotor aerodynamics and acoustic modeling capabilities. This process can be utilized to perform parametric studies on advanced rotor designs. The validated simulation process, along with an optimization routine, can be employed for new low-noise, high-performance rotor systems. This paper evaluates the capabilities of the three aeroacoustic prediction methodologies available within WOPWOP3: compact loading, impermeable surface, and permeable surface. The WOPWOP3 input data made use of CFD methods and rotor comprehensive analysis performance codes calculated for the Bell Model 407. Predicted results were compared to flight test data acquired during the Bell Helicopter 2004 noise abatement flight test program. The prediction methodologies allowed researchers to determine if the effect of advancing tip Mach number and quadrupole noise sources can be accurately predicted for level flight noise levels. It was shown that permeable surface methodology captures the impulsive negative main rotor pressure peak better than the compact and impermeable surface methods when compared to measured data, especially at high-speed forward flight conditions. The permeable surface under-predicted the peak amplitude on average by 0.7 dB.