ISBN 978-3-8439-1957-9

978-3-8439-1957-9, Reihe Strömungsmechanik

Sebastian Türk
Investigation of hybrid turbulence modeling techniques in the context of Fluid-Structure Interaction

120 Seiten, Dissertation Technische Universität Darmstadt (2014), Softcover, A5

Zusammenfassung / Abstract

Within th present work, two different hybrid RANS/LES models, namely DES and X-LES, were investigated. Therefore, the RANS turbulence models available in the inhouse solver FASTEST were extended by the k − ω and k − ω − SST models. Additionally, the DES formulation for both turbulence models as well as the X-LES method were implemented and a new DES formulation, based on the ζ − f model was derived. The correct implementation of the new turbulence models was verified.

It is shown that the X-LES method is more favorable than the DES from a mathematical point of view. These advantages are related to the different coupling between the model equations.

The position of the RANS/LES interface has a major impact on the quality of the final numerical results. Therefore, the influence of the filter width parameter was systematically investigated because of its direct impact on the location of the RANS/LES interface. For different test cases, various filter width criteria were tested and in general, it has been shown that the cell volume based criterion is favorable for the present test cases.

Additionally, the influence of the filter width criterion is demonstrated on a moving mesh. Depending on the chosen criterion, the additional damping, introduced by the model, is directly influenced and thus affects the instabilities in the flow that are necessary for successfully using hybrid RANS/LES methods. Again, it was shown that the cell volume based criterion is favorable.

Subsequently, the performance of the X-LES method was investigated in the context of turbulent Fluid-Structure Interaction for an airfoil with self-adaptive camber. The required structural model was implemented and verified in the present work. A parametric study was conducted, using statistically based turbulence models, in order to investigated the effect of unsteady inflow conditions with various excitation frequencies. For an additional test case, it is shown that the simulation using X-LES provides valuable information at higher frequencies, compared to statistically based turbulence models.

Thus, the present work contributes to the development of hybrid RANS/LES methods by the new DES formulation based on the ζ − f model, but also contributes to the understanding of the performance of hybrid RANS/LES methods on moving grids.