Control of panel response to turbulent boundary-layer and acoustic excitations

Abstract

Nonlinear response of a panel structure results when forced by a subsonic turbulent boundary layer and puretone sound in a wind tunnel. It is a coupled problem, where flow, structure, and sound interact. The structure exhibits a broadband response typical of turbulent boundary-layer loading with superimposed pure tone and harmonics over the band, a process which is statistically stationary, but non-Gaussian. The mechanism is an energy transfer process : the amount of energy supplied to the harmonics is removed from the low-frequency band and the fundamental tone. The objective is to control the nonlinear wave using a time-harmonic actuator tone. Full control is almost achieved using a single controller. Two steps are taken : first, control the harmonics by feeding the energy back into the fundamental and low-frequency band, and second, control the fundamental tone to shift the energy further back into the low-frequency band. Consequently, the response of the panel is reduced to the broadband level of the turbulent boundary-layer excitation, a reduction in peak amplitude power level by 20 dB or more. The experiments are motivated by considerations for aircraft interior noise and structural response.