Large eddy simulation of flow past a square cylinder using finite element method

This dissertation developed an algorithm based on finite element method and large eddy simulation. Primarily, the study reported here investigated the unsteady characteristics of a flow past a square cylinder and forces acting on the surface in order to obtain fundamental information of the characteristics of flow-structure interaction for a slender structure such as a tall building or a bridge.; The research started with development of methodologies for numerical simulation of steady-state and unsteady flows. In order to achieve high computational efficiency with reasonable accuracy, a penalty formulation and an explicit time integration scheme with a segregated Poisson equation for pressure were selected for steady-state and unsteady problems, respectively. The methods employed here were shown to be efficient throughout the computations carried out in the present study. Numerical stability was ensured by use of a streamline upwind scheme for the advection term at the cost of numerical dissipation.; The methods employed for steady-state problems were validated using a class of benchmark problems of laminar flows. The selected problems of lid-driven cavity flow, backward-facing step flow, and a flow past a circular cylinder represented complex flow systems featuring stagnation, separation and reattachment. Those characteristics define a complicated flow around a cylindrical body.; The algorithm developed for unsteady problems was then applied to simulation of a flow past a square cylinder at low Reynolds numbers of 100 and 250. An artificial perturbation to initiate vortex shedding was introduced. Both velocity and pressure fields around the cylinder were well reproduced. Time-averaged statistics of drag and lift from numerical simulations were in good agreement with the compared data. Changes in flow field as well as the appearance of irregularity in resulting forces with the increase of the Reynolds number were reasonably predicted.; The numerical study was extended to the case of a flow past a square cylinder at a high Reynolds number of 22000 in a three-dimensional space using large eddy simulation. Comparisons of the results of two-and three-dimensional computations were made.; These confirmed the eminent three dimensional effects in turbulent flow. Results from the three-dimensional simulation were compared with experimental as well as other computational data. The comparisons were satisfactory, and some of them were in excellent agreement. The compared data included time-averaged statistics and phase-averaged values. Using simulated instantaneous flow fields, the mechanism of vortex shedding as well as three-dimensional flow structures were clearly identified.