Unsteady RANS modelling of flow past a rectangular cylinder: Investigation of Reynolds number effects

The unsteady flow field around a two-dimensional rectangular prism with a fineness ratio (chord-to-thickness) of 5.0, is studied using Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. A non-commercial unstructured flow solver is used in the simulations at various Reynolds numbers (from 26,000 to 1,850,000 based on the chord length), two different angles of attack (0 degrees and 4 degrees) and low Mach number (0.1). A grid-convergence study is presented in order to investigate the dependence of the flow solution on the spatial and temporal discretization. Results obtained with one- and two-equation turbulence models are compared, including models based on the Explicit Algebraic Reynolds Stress (EARSM) approach. The aim of this work is to assess the capability of the computationally efficient two-dimensional URANS calculations to predict the features of complex massively separated flow around this type of geometry. A further goal is to use numerical simulations to investigate the strong Reynolds number effects observed in wind-tunnel experiments. Satisfactory agreement with the wind-tunnel data is obtained for several test cases, but only the turbulence model based on the EARSM approach captured the significant lift increase at non-zero angles of attack due to variation of Reynolds number. This phenomenon is shown to be related to the progressive upstream migration of the time-averaged shear-layer reattachment location on one side of the rectangular cylinder. The effects of the Reynolds number on the mechanism of vortex shedding are also explored in the simulations. (C) 2010 Elsevier Ltd. All rights reserved.