High fidelity fluid-structure turbulence modeling using an immersed-body method

Abstract

There is an increasing need for turbulence models with fluid-structure interaction (FSI) in many industrial and environmental high Reynolds number flows. Since the complicated structure boundaries move in turbulent flows, it is quite challenging to numerically apply boundary conditions on these moving fluid-structure interfaces. To achieve accurate and reliable results from numerical FSI simulations in turbulent flows, a high fidelity fluid-structure turbulence model is developed using an immersed-body method in this thesis. It does this by coupling a finite element multiphase fluid model and a combined finite-discrete element solid model via a novel thin shell mesh surrounding solid surfaces.

The FSI turbulence model presented has four novelties. Firstly, an unsteady Reynolds-averaged Navier-Stokes (URANS) k−ε turbulence model is coupled with an immersed-body method to model FSI by using this thin shell mesh. Secondly, to reduce the computational cost, a log-law wall function is used within this thin shell to resolve the flow near the boundary layer. Thirdly, in order to improve the accuracy of the wall function, a novel shell mesh external-surface intersection approach is introduced to identify sharp solid-fluid interfaces. Fourthly, the model has been extended to simulate highly compressible gas coupled with fracturing solids.

This model has been validated by various test cases and results are in good agreement with both experimental and numerical data in published literature. This model is capable to simulate the aerodynamic and hydrodynamic details of fluids and the stress, vibration, deformation and motion of structures simultaneously. Finally, this model has been applied to several industrial applications including a floating structure being moved around by complex hydrodynamic flows involving wave breaking; a blasting engineering simulation with shock waves, fracture propagation, gas-solid interaction and flying fragments; fluid dynamics, flow-induced vibrations, flow-induced fractures of a full-scale vertical axis turbine. Some useful conclusions, e.g. how to model them, how to make them stable and how to predict when they will break, are obtained by this FSI model when applying it to the above applications.