Computational studies of massively separated wake flows of transport aircraft

Abstract

This work focuses on the investigation of flow phenomena associated with low speed stall using a representative commercial transport aircraft configuration. Subsonic stall at high Reynolds number involves a highly complex turbulent flow field, which is difficult to analyze in ist entirety via experimental methods. Various computational approaches based on URANS and hybrid RANS/LES were evaluated, utilizing validation data from the European Transonic Windtunnel. Scale-resolving computational approaches were leveraged to gain deeper insight into the processes occurring in such a wake. DDES-based methods were found to be able to resolve the flow features occurring at the separation location and in the wake. An extensive study on the impact of solver settings, computational grids, model geometry and inflow Reynolds number was carried out in order to permit a validation of the chosen approach. Using these findings, the massively separated wake flow was studied at three angles of attack in post stall conditions. Three different regimes of formation of the separated wake were identified via the main locations where turbulence kinetic energy is produced. Analysis of anisotropy, turbulence length scales and signal characteristics provided insight into the propagation of the wake and the mixing processes. Modal analysis of the wake dynamics enabled the detection of a near-wing recirculation area and a von Kármán vortex street in the wake. Flow structures associated with both phenomena result in tailplane load fluctuations at their respective characteristic frequencies.