Numerical prediction and characterization of shock-buffet in transport aircraft

Computational Fluid Dynamics (CFD) simulations are frequently used in the aerospace industry to help reduce development times by cutting down on the need of extensive windtunnel campaigns. However, although design-point aerodynamics are well predicted, edge of the envelope scenarios dominated by non-linear fluid phenomena can lead to uncertainties in the accuracy of the results produced. This work addresses the use of Reynolds-averaged Navier-Stokes (RANS) based simulations in the prediction of unsteady shock-buffet phenomenon. Three studies are conducted: a 2D validation study, a 3D validation study, and the pinnacle of this work which presents a novel shock-buffet prediction on an industrially-relevant aircraft confguration. Two dimensional shock-buffet predictions are presented as a confrmation of previous available knowledge. The dependency on turbulence modelling approaches is evident, with new results showing that the full Reynolds Stress Model (RSM) is a more appropriate closure to the RANS equations than other typically used eddy-viscosity-based models. However, this implies additional computational costs (due to increased number of equations solved), and inherited challenges associated with solver stability. RANS-based simulations are then applied to a 3D confguration: the NASA Common Research Model (CRM) wing-body test case. Complementary results to the AIAA CFD Drag Prediction Workshop are produced. Novel results, outside the Drag Prediction Workshop envelope, investigate the development and expansion of the shock-induced boundary layer separation on the NASA CRM wing, however the steady RANS approach fails to accurately predict this due to unsteady effects which are not accounted for. Unsteady simulations in the shock-buffet regime of the wing-body NASA CRM are then presented as the main novel contribution of this work. The complexity of the phenomenon is revealed by unsteady shock oscillations coupled with shock-induced separation and vortex shedding. The presence of shock-buffet cells is detected and helps understand shock dynamics. A frequency analysis reveals the presence of multiple peak frequencies. A qualitative comparison with experimental observation show similarity in the physics produced. Finally, to further investigate the shock-buffet phenomenon, the effects of changing the Reynolds number are presented. Through industrial relevance, the current work can lead to decision making in the development of the future generation of aircraft