Algorithm for the nonlinear propagation of broadband jet noise

A frequency-domain algorithm for nonlinear noise propagation is presented. The propagation of noise generated by very high-speed jets exhibits nonlinear effects. This nonlinear behavior, which includes the transfer of energy to high frequencies, is captured in the present algorithm. The generalized nonlinear Burgers equation, which includes atmospheric absorption and dissipation, is solved for the pressure signal in the frequency domain. The results are then obtained as a function of time. A test case of a sinusoidal wave is considered, and the results are compared with the existing analytical Blackstock Bridging Function and Fubini solutions. The predicted results of the sinusoidal wave case agree fairly well with the analytical results. Jet noise data from the Boeing Low Speed Aeroacoustic Facility are used for the broadband noise prediction. The experimental and predicted power spectral density plots are compared for microphones at different radial locations. The predicted results are in good agreement with the experimental results at all the microphone locations, and the power spectral density plots show a lift at high frequencies due to the nonlinear steepening of the waves. The skewness of the experimental and predicted signal is discussed for the Boeing data. Full-scale data acquired during a tie-down test of the F/A-18E are propagated using the nonlinear and linear predictions, and the differences in the results are discussed. Ground reflection effects are then presented for both the Boeing and F/A-18E engine data.