THREE-DIMENSIONAL NUMERICAL SIMULATIONS OF FLOWS PAST SMOOTH AND ROUGH / BARE AND HELICALLY STRAKED CIRCULAR CYLINDERS ALLOWED TO UNDERGO TWO DEGREE-OF-FREEDOM MOTIONS

摘要

We simulate the flow past smooth and rough rigid circular cylinders that are either bare or outfitted with helical strakes. We consider operating conditions that correspond to high Reynolds numbers of 10~5 and 10~6, and allow for two degree-of-freedom motions when the structure is allowed to respond to vortex-induced cross flow and in-line forces. The computations are performed using a parallelized Navier-Stokes in-house solver using overset grids. For smooth surface simulations at a Reynolds number of 10~5, we use a Smagorinsky Large Eddy Simulation (LES) turbulence model and for the Reynolds number cases of 10~6 we make use of the unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with a two-layer k-epsilon turbulence model. The rough surface modifications of the two-layer k-epsilon turbulence model due to Durbin et al. (ASME J. Fluids Eng., 2001) are implemented to account for surface roughness effects. In all our computations we aim to resolve the boundary layer directly by using adequate grid spacing in the near-wall region. The predicted global flow parameters under different surface conditions are in good agreement with experimental data and significant VIV suppression is observed when using helically straked cylinders.