Modeling Far-field Acoustical Nonlinearity from F-35 Aircraft during Ground Run-up

The high noise levels associated with full-scale military aircraft result in nonlinear propagation, which results in acoustic shock formation and can alter noise perception. This propagation has been modeled for other aircraft but previous studies have been limited in scope, showing results for only select engine conditions and angles. Recent data measured near an F-35B allow for a more complete analysis of nonlinear propagation. Visual inspection of waveforms shows shock formation and persistence out to distances of up to 1220 m. Using an algorithm based on the Burgers equation, modified to include weak shock theory and an empirical correction for meteorological and ground effects, nonlinear and linear predictions are compared to measurements over a broad range of angles at 305 m. These analyses show that nonlinear effects become important in the maximum radiation direction at 75% thrust and increase with engine condition. At high engine powers, evidence of nonlinear propagation is found in the forward direction.