Fluid-structure interaction of large amplitude structure vibrations and moderately high Reynolds number turbulent flows

Fluid-structure interaction (FSI) effects often must be considered when flexible structures are subjected to unsteady flows. Large-scale unsteady flows may excite structural vibrations significantly and cause the fluid flow to be altered by the large amplitude vibrations. In this research, a partitioned FSI modeling approach is employed to simulate such large amplitude structural vibrations interacting with turbulent flows. The partitioned approach is based on the fixed-point iteration scheme that tightly couples the in-house finite-element structural code FEANL and the open-source computational-fluid dynamics (CFD) library package Open- FOAM. For turbulent flow predictions, hybrid turbulence models such as Delayed Detached-Eddy-Simulation (DDES) and k-o SST-SAS are employed. Both of the models are capable of simulating highly unsteady and separated turbulent flows. The simulations conducted in this work are as follows; vortex-induced vibration of a flexible plate (2-dimensional), a rigid-fixed and self oscillating cylinder at Re = 5,000 (3-dimensional), a hydrofoil vibration due to strong upstream vortices in a 12"-diameter water tunnel, and a propeller in a crashback condition. Modeling difficulties of these cases increase in terms of flow dimensionality (2- or 3-dimensional), flow type (laminar or turbulent), temporal and spatial resolution, etc. Therefore, the order of the simulations presented from Chapters 3 through 5 is consequential in that the simulation cases of Chapter 4 are not possible without Chapter 3 and, Chapter 5 likewise. The objective of the rigid-fixed and self oscillating cylinder simulations is to perform CFD and FSI validation studies. After the validation work, the CFD and FSI solver are extensively employed to simulate the aforementioned cases. In all of the simulations performed in this work, comparisons against numerical and experimental data available in the field of fluid-structure interaction are extensively performed. The results of the fixed cylinder simulation show that the unsteady, separated and shedding flow field is well captured. In particular, the force statistics (lift and drag coefficients), correlation of pressure and pressure profiles show good agreement with experimental data. For the self-oscillating cylinder simulation, vibration amplitudes in lock-in shows favorable agreement with experimental data, and especially, the amplification of drag coefficient due to vibration shows great agreement with both analytical and experimental data. For the flexible hydrofoil simulation, results show that the structural response is well captured based on comparisons against tip deflection and reaction force experimental data. Time-averaged flow fields are compared with the particle-image velocimetry (PIV) and laser-Doppler velocimetry (LDV) data. Numerical and experimental flow field data exhibit good agreement both qualitatively and quantitatively. The results of the rigid propeller simulation show that the unsteady flow field and fluid force imparted on the propeller are well resolved compared to numerical and experimental data published in the propeller research field. This case was used to quantify the anticipated CPU requirements for an FSI simulation of a flexible propeller in a crashback condition. While the CPU requirements were too significant to allow for such a simulation in the present research, they are not prohibitive considering available computation capabilities of typical high-performance computing clusters.