Up in the Air: In-Flight Wavenumber Characterization of Surface Pressure Fluctuations at Transonic Conditions

One way of representing surface pressure fluctuations is to display them in frequency-dependent wavenumber spectra. They can be used to feed structural vibration predictions model. However, mostly models and experimental data from wind tunnel and water tunnel experiments have been employed. Apart from possible scaling effects, only hydrodynamic pressure fluctuations are incorporated in these models. Some data from flight tests exists, but again this data is limited to sections of the aircraft where the hydrodynamic pressure fluctuations are dominant. In order to consider both, acoustic and hydrodynamic surface pressure fluctuations in flight a beamforming approach is used in the following to determine wavenumber spectra of pressure fluctuations in cruise flight. This allows for the simultaneous characterization of both, hydrodynamic and acoustic pressure fluctuations and for the discrimination between the two. The wavenumber spectra can be used directly as input for the prediction of structural vibration.