Assessment of the Contribution of Panel Vibration to Airframe Noise

Abstract

Aerodynamic noise sources not associated with propulsion are termed “airframe noise.” As well-known sources such as flow separation, landing gear vortex shedding, and flap-edge noise are further reduced, the noise sources from the clean airframe will need to be better understood. Although direct radiation from boundary layers is generally agreed to be an insignificant source, the boundary-layer surface pressures can drive the panels to excitation levels that may produce significant airframe noise. An estimate of airframe noise due to structural vibration is presented. This analysis shows that panel vibration driven by turbulent boundary-layer fluctuations can produce airframe noise levels comparable to those measured on aerodynamically clean airframe configurations. The analysis contains a number of engineering approximations, which are discussed along with their implications for either over- or underestimating the acoustic radiation results. Because the analysis shows levels comparable to measured data rather than dramatically lower levels, it is concluded that structural vibration may be a potentially important source of airframe noise and deserves further study.