Vibro-acoustic analysis of flight test data comprising fuselage vibrations, external pressure and interior cabin noise measurements

Abstract

In the years 2011 and 2012, a series of flight tests with DLR’s A320-232 research aircraft ‘D-ATRA’ were carried out within the German national (LuFo IV) project SIMKAB with the objective to improve cabin acoustics comfort in passenger aircrafts. In order to study the source mechanisms responsible for aircraft cabin noise, an extensive flight test campaign was carried out that considered multiple flight and operational conditions of the aircraft. For the global analysis of this problem, structure-borne noise as well as airborne sound sources must be considered. Hence, an extensive data set was collected that consists of vibration measurements of the fuselage primary structure and cabin interior, unsteady surface-pressure for characterization of the turbulent boundary layer, engine induced external sound pressure and sound pressure inside the cabin. In total, 154 vibration signals, 38 unsteady pressure signals, 80 external microphones and 66 internal microphones have been used in more than 300 different flight conditions. In the current paper, the main focus is given to the medium frequency range and in particular to the vibration analysis since the acceleration of the fuselage acts as an intermediate element between sources and receivers. The different flight conditions evaluated considered different flight speeds, flight levels, engine operation conditions, etc. The analysis included, among others, the correlation of all acquired data in order to investigate the energy transfer mechanisms. Results show consistency of the expected relation between dynamic pressure and vibro-acoustic responses for such problem. Evidence indicates a clear structure-borne influence of engine related vibrations at low frequencies, whereas cabin noise at middle-high frequencies is driven by the turbulent boundary layer. This project was supported by the Federal Ministry for Economic Affairs and Energy on the basis of a decision by the German Bundestag.