Effect of cross-confinement on unsteady wake characteristics of circular cylinder immersed in shear flow

摘要

Present study investigates effect of cross-confinement on three-dimensional unsteady wake characteristics in flow past circular cylinder mounted on a surface using OpenFOAM. Aspect ratio (ratio of height to diameter of the cylinder) is kept fixed equal to four. Temporal wake behaviour has been characterised at fixed Reynolds number equal to 200 using Hilbert Huang transformation of transverse velocity signals. Frequency and energy distributions of component signals have been illustrated with the help of Hilbert spectra. Variation in frequency of vortex shedding with the change in shear intensity and top confinement has been illustrated in marginal spectra. Quantification of nonlinear fluctuations in the wake has been presented in terms of degree of stationarity. Spatial and temporal evolutions of vortex modes (frequency and growth rate) have been examined using recently developed snapshot-based technique 'dynamic mode decomposition (DMD)'. Periodic behaviour of the wake has been illustrated using recurrence plot (RP) and different quantification estimates are presented based on patterns that appear in the RP.