Simulations of Flow Around Bluff Bodies at High Reynolds Numbers

Guilherme Vaz de Almeida Fontes Neves

Key information

Authors:

Guilherme Vaz de Almeida Fontes Neves (Guilherme Vaz de Almeida Fontes Neves)

Supervisors:

Luís Rego da Cunha de Eça (Luís Rego da Cunha de Eça)

Published in

01/27/2021

Abstract

The flow around bluff bodies has been extensively studied in computational fluid dynamics (CFD), with the circular cylinder as the prime subject of investigation. Motivated by the project of a complex off-shore aquaculture structure, this work focuses on statistically unsteady flow around bluff bodies of different cross-sectional shape. Two preliminary studies were performed. The Reynolds-Averaged Navier Stokes (RANS) equations are used for modeling and closed with turbulence models (KSKL and k-omega SST). The first preliminary study aims to check the convergence properties of unstructured grids. The flow around two-dimensional infinite cylinders at Re=1000 with circular, hexagonal and octagonal cross-sections was simulated in order to compare with the available literature. The unstructured grids showed to be able to accurately perform the simulations. The second preliminary study presents the calculations of the flow around two-dimensional cylinders at Re=10^8 with circular, octagonal and hexadecagonal cross-sections in order to assess the impact of the use of wall functions in the numerical and modeling error at very high Reynolds numbers. The results showed a significant improvement in numerical robustness with the use of wall functions, especially for the polygonal geometries. The two preliminary studies led to a set up of the 3D study of flow around the aquaculture structure at Re=10^8 made up of unstructured grids with wall functions. Estimations of the average forces and moments acting on the structure were presented, as well as the frequency content, which will allow for an accurate structural analysis in the future.