Fuselage Excitation during Cruise Flight Conditions: Influence of Different TBL Wavenumber-Frequency Models on Structural Response

Abstract

In the last fifty years many semi-empirical models to predict surface-pressure fluctuations beneath turbulent boundary-layers (TBL) have been developed for a large variety of test conditions. Nowadays, the relevance of the TBL as a source of cabin interior noise is steadily increasing due to quieter aircraft engines. Beside the auto-spectra, which characterize the strength of the TBL excitation at one point, spatio-temporal information is important to describe the excitation. For numerical structural excitation response calculations the spatio-temporal information is typically modeled in terms of the wavenumber-frequency spectrum. It gives information about the development of turbulence over space and time. This paper briefly reviews available published models to estimate this behavior. Furthermore, the influence of these different models, when numerically coupled to structures, is systematically examined. Firstly, systematical testing is performed on simply supported flat plates by using two methods; a method developed by Graham and a commercial software package using Statistical Energy Analysis (SEA). Secondly, tests on Airbus aircraft structures are performed by using SEA. Necessary aerodynamic input data are not taken from flat plate estimates but from CFD calculations as performed with DLR's in-house RANS solver TAU. Finally, calculation results of the structural vibration are compared with measured structural vibrations of the aircraft primary structure at cruise flight conditions. Beside the results from published semi-empirical wavenumber-frequency models also predictions with DLR's Fast Random Particle-Mesh Method (FRPM) of the spatio-temporal TBL behavior are presented for Airbus aircraft in cruise flight conditions.