Studies on the Development of Massively Separated Wakes of Aircraft

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The behavior of commercial aircraft at the flight boundaries is associated with complex fluid-physical processes, the characterisation of which presents a challenge both experimentally and numerically. Flow separation occurs on the wing at high angles of attack, resulting in an unsteady turbulent wake. These turbulent structures are propagated downstream and interact with the tail plane. The main focus of this research project is the study of the interaction between flow separation, wake propagation and its interaction with the tail plane.The project focuses on the CRM aircraft configuration and associated measurements carried out during the EU project ESWIRP in the European Transonic Wind Tunnel (ETW) on the generic CRM aircraft configuration. During the course of the first project phase, the processing of time-resolved PIV wake measurements was completed. The suitability of modern scale-resolving numerical methods for the simulation of separated wake flows was investigated. Synergetic analyses of the experimental and numerical data have provided insights into the formation and behavior of massively detached wake flows at high angles of attack. Statistical and spectral analyses of the data sets have shown that the numerical methods are suitable for the prediction of the flow physics and the turbulent fluctuations in the wake.In the second project phase, the gained knowledge will be used to carry out in-depth analyses of the wake physics. The first step is to examine to what extent the differences between the computational and experimental studies influence the comparability of the results. In addition to the investigations carried out in the first phase at a high angle of attack and massive separation, smaller angles of attack will now also be considered in order to analyze flight conditions involving a smaller scale flow separation. To this end, hybrid RANS/LES methods suitable for these flow conditions will be identified first. Specific validation of the methods will involve both the existing ESWIRP measurement results and, in addition, wind tunnel measurements carried out at the applicant's department using a simplified configuration. Based on previous findings, the influence of the tail plane on the wake will be analyzed. For this purpose, investigations will be carried out under consideration of different tail plane incidence angles and, as a reference, without the tail plane. Fluid physics studies will be based on statistical and spectral analyses as well as modal methods such as POD or DMD, whereby both the transient fluctuations in the wake and the fluctuating wing and tail plane loads will be examined in detail. The variations of the angle of attack and tail incidence serve to obtain an enhanced understanding of the behaviour of the separated wake and its interaction with the tail over a wide range of possible inflow conditions.