Aerodynamic and Aeroacoustic Analysis of a Multi-Element Airfoil using Hybrid RANS/LES Modeling Approaches

Licentiatavhandling, 2012

Global hybrid RANS/LES simulations were used for computing the turbulent flow around a three-element airfoil. Based on the results of the flow computations, a comprehensive analysis of the flow properties was performed. The mean pressure distribution obtained from the simulations, was found to be in excellent agreement with experiments, when using an adequate spanwise domain extent and spanwise grid resolution. Initially, strong delays of the slat shear layer instability were observed, which could be overcome partly by adapting the grid resolution. Moreover, unsteady flow data from the hybrid RANS/LES simulations was extracted at a permeable surface in the near-field of the airfoil and used as input for wave propagation calculations. Those calculations were done via three acoustic analogies, namely the Kirchhoff analogy, the Ffowcs-Williams and Hawkings analogy and the Curle analogy. In the present acoustical analysis, the performance of the three acoustic analogies is investigated. The noise contribution of all three elements of the airfoil was studied as well as their emission behavior. Along with the aerodynamic and aeroacoustic analysis of the high-lift flow, hybrid RANS/LES modeling has been considered. As the so-called gray area problem of hybrid RANS\slash LES methods was encountered for the shear layer emanating from the slat cusp, several alleviation techniques were implemented and tested for a fundamental mixing layer flow.