Abstracts Category : Other

On the Simulation of Turbulent Fluid-Structure Interaction

by Awais Ali

The fluid-structure interaction (FSI) phenomena are relevant in a significant number of naturally occurring as well as industrial applications. Simulations of FSI have gained noteworthy attention with rapid advancements of computational technology in the last decade. Efficiency and accuracy of these simulations are still a concern, specially with a turbulent flow, the challenge is compounded by an additional computational cost for a turbulence modeling approach. Partitioned coupling approaches owing to software modularity and reusability are favored by engineers to solve FSI problems. The turbulence in flow is simulated through models with varying levels of complexity and computational requirements. In industrial applications, the use of Reynolds Averaged Navier Stokes (RANS) modeling of turbulence is dominant, whereas turbulence resolving approaches like Large-Eddy simulation (LES) are still not considered feasible due to computational requirements. To get as much accuracy by using as least as possible computer resources, a reasonable compromise are hybrid RANS-LES of turbulence, which are becoming more and more frequent.The goal of this work is to enable efficient and reliable simulations of FSI in turbulent flow. To this end, validation studies of three different turbulence modeling approaches available in the in-house flow solver FASTEST are performed. The structural subproblem in the coupling environment is solved with the Finite Element Method based code FEAP, while the data transfer and interpolation on non-matching grid interfaces can be handled with MpCCI or preCICE.For this work, the turbulence modeling approaches in FASTEST are extended with an implementation of the Wall Adapting Local Eddy (WALE) viscosity model for LES, and a validation study of the model is performed for a two dimensional periodic hill flow test case. An economical method based on a Poisson equation for the calculation of the nearest wall distance is also implemented, which is required by some turbulence models. The accuracy of the method is assessed with two computations on stationary grids. In turbulent flow simulations with moving grids, the height of cells on a wall changes and it can make a wall treatment approach unsuitable. This issue is addressed with an implementation of wall boundary conditions that work regardless of the first cell position in a boundary layer. The implementation is tested on stationary grids in a channel flow with a variation of the first cell height on the wall. A test of the method with an FSI test case showed satisfactory results.Validation studies of a RANS and a hybrid RANS-LES approach are performed with simulations of two FSI test cases. The two and three dimensional RANS and the hybrid RANS-LES produce a good agreement with the experimental results for oscillation characteristics of the structure. A hybrid RANS-LES and an LES is performed for another FSI test case with a very dense mesh. The LES and the hybrid RANS-LES on two different, but relatively dense meshes produced very similar resultsAdvisors/Committee Members: Schfer, Michael (advisor), Janicka, Johannes (advisor).