Three-Dimensional Unsteady Wake Characteristics of Rectangular Cylinder

Abstract

Present study investigates three-dimensional flow field characteristics for flow past surface mounted finite height rectangular cylinder using Open Source Field Operation and Manipulation (OpenFOAM). Wake characteristics have been examined for different values of Reynolds number (Re) ranging from 140 to 200 and fixed height of the cylinder. Different values of side ratio (SR, ratio of longitudinal dimension to transverse dimension of the cylinder) have been considered varying from 0.5 to 3.0 for Re = 180. Effect of Re on unsteady wake flow has been presented using iso λ2 -surfaces. Unsteady periodic oscillation and effects of Re and SR on wake transition have been illustrated using Hilbert spectra of the transverse velocity signals in the wake. Wake shedding frequency and its distribution in energy frequency domain have been presented and analysed using marginal and Fourier spectra. Comparison between the two spectra reveals that marginal spectra extract lowest frequency which is not captured by Fourier spectra. Extent of nonlinear fluctuations in the wake and its distribution with the associated frequency have been analysed and quantified in terms of degree of stationarity. Variation in mean drag coefficient with change in Re and SR has also been reported.