Numerical simulation of wake vortex flows: RANS-LES of a fuselage wake and LES of wake vortices in ground effect with and without wind

The present document reports on the numerical simulations performed by Cenaero within the European Union funded FAR-Wake project. This project, the acronym of fundamental reseach on aircraft wake phenomena, is mainly devoted to the alleviation of wake turbulence problem behind civil aircraft. In the far-field, the wake of an aircraft is composed of large-scale swirling flow (vortices) that can represent a significant hazard for the following aircraft. This has therefore a major importance in practical applications like safety and capacity of air transport. The first contribution of Cenaero was to investigate the near-field wake generated by the fuselage of an aircraft by means of steady simulations (RANS) as well as unsteady simulations (hybrid RANS-LES), and this, in order to discriminate the influence of each aircraft element to the global wake. The second contribution of Cenaero was dedicated to the study of the unstability mechanisms occuring to longitudinally uniform two-vortex system in ground effect. This has a major importance as it correponds to configurations representative of the take-off and landing phases. Furthermore, the influence of atmospheric conditions was investigated in the form of unsteady turbulent winds (a headand a cross-wind) advecting the vortices. This far-field study was done using three-dimensional unsteady simulations (LES). 1 RANS-LES of a fuselage wake (near-field study) The first contribution of Cenaero was performed within the Workpackage 2.2 devoted to the investigation of the proper influence of each aircraft element to the global wake during free-flight conditions : contribution of fuselage, the wings, the nacelles, the flaps and slats. The scope of the present study, although extremely challenging and large, is limited to the near-field of the aircraft, in the sense that the region of interest of the simulations is rather close to the aircraft geometry, well before the end of the roll-up process. The selected geometry is a four-engines generic aircraft, the TAK model of the Technische Universitat Munchen (TUM) [1], presenting a wingspan of approximatively 3m. On one hand, hot-wire measurements of the aircraft wake were performed in the TUM windtunnel, see Fig. 1, by Alexander Allen and Christian Breitsamter [1]. On the other hand, numerical simulations were made by the German Aerospace Center (DLR) using their unstructured flow solver, Tau [8], and by Cenaero using their unstructured flow solver, Argo. The DLR investigated all the geometrical configurations, defined by distinct combinaisons of different aircraft elements, in accordance with the TUM experiments. The DLR computations by Stefan Melber, reported in deliverable [11], were performed using steady Reynolds-Averaged Navier-Stokes (RANS) approaches, based either on the k − ω model [12] or the Reynolds Stress model (RSM), the last model presenting a better behaviour in vorticity-dominated flows. On the contrary, Cenaero only focused on one single geometry presenting a rather limited level of complexity, the fuselage alone. The reason behind this choice was to test the ability of advanced simulations methods to better capture the physics of such a flow. In fact, the Cenaero simulations were not only performed using a steady RANS model, here using the one-