Fuselage Excitation During Cruise Flight Conditions: Measurement and Prediction of Pressure Point Spectra

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. The possibility of predicting surface pressure auto-spectra with the various publicly available semi-empirical models at several positions on the fuselage of DLR's Advanced Technology Research Aircraft (ATRA) is investigated. A large validation database was used, involving in-flight measurements at different flight levels (FL) and Mach numbers, applying two different sensor types. Predictions were performed based on semi-empirically estimated TBL parameters (partly included in the different models) and, additionally, based on TBL properties that were extracted from CFD simulations. This procedure served to identify different sources of error in the prediction. Overall, it is shown that today's models provide a large (> 10 dB) scatter among the predicted spectra. Even the most suitable approaches are not generally applicable to all relevant positions at the fuselage. Particularly in regions with strong pressure gradients and high turbulence kinetic energy measured auto-spectra cannot be reproduced with sufficient accuracy. This indicates the need for more universally applicable CFD-and CAA-based surface pressure prediction methods.

Fuselage boundary-layer refraction of fan tones radiated from an installed turbofan aero-engine

“…Recently some realistic predictions were in Ref. [14]. In this paper the maximum thickness (99%M ∞ ) is around 0.1a 0 in the plane of the engines.…”

Simulation of Surface Pressure Fluctuations on an Airbus-A320 Fuselage at Cruise Conditions

“…The Green function for the convected wave equation is The surface pressure fluctuations measured from the flight tests [18,19] showed similar features to those in incompressible flows. Furthermore, the turbulent boundary layer induced acoustic pressure was found out to be negligible compared with the hydrodynamic pressure fluctuations on the fuselage surface [23].…”

“…Eqs. (18)(19), ρ denotes the mean air density, and the density fluctuations are not considered because they are negligible compared to the mean air density for the considered Mach number (estimated to be approximately 1%) according to Gerolymos and Vallet [31].…”

“…Numerical investigations on high-speed flows, however, only for low Reynolds number flows were carried out by Gloerfelt & Berland [11], Duan et al [12] and Cohen & Gloerfelt [13]. Results of in-flight tests were published by Bhat [14], Palumbo [15,16], Haxter & Spehr [17,18] and Klabes et al [19]. In the most recent flight tests performed with DLR's Airbus-A320 Advanced Technology Research Aircraft (ATRA) [20], a pressure transducer array with a quasi-randomized distribution was applied in the flight tests.…”

Assessment of a Turbo-Electric Aircraft Configuration with Aft-Propulsion Using Boundary Layer Ingestion

“…The boundary layer theory applied did not include any pressure gradient, and all the integrated fuselage friction was directly translated into a corresponding average total pressure loss. This treatment of the incoming boundary layer, despite being practically applicable and reasonably representing the prevailing flow physics at conceptual level, is only a first order estimate and the incoming momentum deficit largely depends on the fuselage and intake design, as well as the respective diffusion (and also the real boundary layer height may be substantially smaller or bigger [19]). Hence, the uncertainty in predicting the real achievable incoming momentum deficit was considered in a sensitivity study.…”