| Popis: |
When trying to predict the acoustic experience in aircraft cabins during flight, it is of importance to characterize the possible excitation mechanisms. In the following, we will focus on the fuselage surface pressure fluctuations on the outside of the aircraft hull and to determine its characteristics. The primary focus of this chapter is set on measurement and data processing rather than a deep interpretation of the results found. Flight test measurements using a pressure transducer array installed in window banks at two longitudinal positions on the fuselage are examined. The main focus is set on distinguishing between acoustic and hydrodynamic pressure fluctuations by means of phase propagation velocity. Differentiation between propagation velocities is achieved per-frequency by means of a wavenumber representation of the surface pressure fluctuations: at constant frequency, different propagation velocities will result pressure fluctuations to appear at different locations in the domain. A wavenumber filter can then be easily applied to separate pressure fluctuations with different characteristics. Prior to filtering, a deconvolution scheme is applied to the wavenumber maps in order to attempt to remove the array pattern from the resulting images, thus increasing resolution. The analysis results in two separated frequency spectra for acoustic and hydrodynamic pressure. |
