Numerical Analysis of Jet Engine Perturbations on the Buffet Phenomenon

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The transonic flow over wings is characterized by the occurrence of local supersonic flow regions which are terminated by a shock wave the strength of which increases with freestream Mach number and angle of attack. Above a sufficient strength, the shock wave induces flow separation which under certain flight conditions due to the interaction between the detached flow and the shock wave results in self-excited periodic shock oscillations, which are denoted buffet. The buffet phenomenon defines an extremely critical load state for the overall flight stability. Regarding the ever-increasing importance of virtual flight tests and the necessary optimization of the weight of the essential supporting structure, it is essential to exactly predict and to understand in detail the impact of perturbations in the flow field on the onset and existence of buffet. Due to the ecologically and economically driven development of modern, more efficient UHBR-engines (Ultra-High Bypass Ratio) with increasing diameter and their pronounced vicinity to the wing, stronger unsteady intricate interactions between the engine jet and the flow over the wing occur which are significant for the aerodynamic integration of the engine. Within the scope of TP1, the influence of the disturbances introduced by the integration of a UHBR engine and, in particular, the influence of the associated engine jet consisting of the hot core and the cold bypass flow will be analyzed. An essential part of the investigations is the analysis of the acoustic field resulting from the flow in the vicinity of the trailing edge, which is a central element of established buffet models and is significantly influenced by the integration of the engine. To quantify this influence, highly resolved simulations of the flow field and the resulting acoustic field are performed on the Airbus XRF-1 configuration at flight-relevant Reynolds numbers. For this purpose, a directly coupled approach consisting of wall-modeled large-eddy simulations and the simultaneous solution of the acoustic perturbation equations is followed. For the detailed analysis of the dynamics, TP1 in particular relies on empirical mode decomposition. This method makes no prior assumption regarding the mathematical form of the investigated dynamics, and thus is particularly well suited for the analysis of the highly nonlinear transonic flow field underlying the buffet phenomenon. The simulations are carried out in close cooperation with the project partners and the accompanying ETW measurement campaign. Thus, there is a constant exchange of data and knowledge between the project partners to conduct a coherent and complex investigation of the buffet phenomenon.