A Large Eddy Simulation Based Fluid-Structure Interaction Methodology with Application in Hydroelasticity

Doktorsavhandling, 2013

The phenomenon of hydroelasticity is a subarea of Fluid-Structure Interaction (FSI) and of major importance in many engineering applications related to hydrodynamics and naval architecture e.g. wave-induced vibrations, such as springing, whipping and slamming, propeller singing, composite propellers or turbines, acoustic signatures from naval vessels, highly loaded thin propeller blades, and cavitation erosion. Some of these phenomena can be assessed with reasonable reliability, but in cases where medium- to small-scale flow features are important the computational models need to be further developed to improve predictive capability and enable new conceptual designs. The work presented in this thesis has this kind of development as objective and a method capable of providing hydroelasticity predictions based on LES is presented and validated. The problem is particularly challenging as the densities of the fluid and the structure are comparable and an implicit coupling is thus needed to ensure a stable solution procedure. Furthermore, LES is not well established in the FSI context and especially not within the area of hydroelasticity. High resolution of the computation is necessary and the algorithm needs to run efficiently on large parallel computer systems. Reliable results also include predicting the correct separation pattern, in general on smoothly curved geometries. To address this a validation of LES in terms of predicting the correct separation pattern was performed and presented here, including also the development and validation of a LES turbulence trip model. The results presented can be divided into three parts, firstly the prediction and validation of open separation phenomena around a prolate spheroid, secondly the prediction and validation of the flow around an oscillating cylinder and thirdly the development of a fluid-structure interaction methodology for hydrodynamic applications and corresponding prediction and validation of the deformation of a flexible hydrofoil. The results all show a good agreement with experimental data, thus supporting the validity of the fluid-structure interaction methodology for hydroelastic applications presented within the scope of this thesis. Finally, the parallel performance of the implementation is analyzed through both weak and strong scaling and found to be satisfactory.