Effect of incoming shear on unsteady wake in flow past surface mounted polygonal prism

Abstract

Three-dimensional numerical investigations for flow past surface mounted finite height prisms of different cross sections (circular, square, and triangle with apex and base facing) have been carried out using Open Source Field Operation and Manipulation. A general code has been written to consider the effect of impinging shear flow using GroovyBC and is integrated with the existing solver. The effect of impinging shear at the inlet (shear intensity, K) on three-dimensional vortex structures has been explored using iso-Q surfaces for the varying Reynolds number (Re) ranging from 60 to 200 and fixed aspect ratio equal to 5. Three different vortex shedding regimes have been investigated based on values of Re and K, viz., steady flow, symmetric, and asymmetric modes of vortex shedding. Interwave and intrawave frequency modulations and their effects on wake oscillation have been illustrated using Hilbert spectra of transverse velocity signals in the wake. Effects of K and Re on wake oscillation frequency have been presented in terms of marginal spectra of the velocity signals. The extent of nonlinear fluctuations in the wake has been quantified in terms of “degree of stationarity.” Moreover, different modes with their associated frequencies and growth rates that are responsible for transition from the asymmetric to the symmetric mode have been discussed using the computational technique named “Dynamic Mode Decomposition.” Variation in the mean drag coefficient with the change in values of K and Re has also been reported.