Three-dimensional numerical investigations have been carried out in flow past finite-height cylinders mounted on a horizontal plate surface in presence of incoming nonuniform shear flow. Spatial and temporal characteristics of the unsteady wake are investigated behind bluff bodies (circular, square, rectangular, elliptic, triangle with apex and base facing cylinder) using C++ OpenFOAM (Open Source Field Operation and Manipulation) code based on finite volume method. Computations have been performed and three-dimensional flow structures are investigated for flow past two inline and side-by-side arrangements of cylinders mounted on a plate surface. Depending up on inter-cylinder spacing, three-different modes, i.e. single slender mode, reattachment mode, binary mode have been reported. Effect of shear intensity on dynamic characteristics is reported for different cylinder cross-sections.
The spatial structures of the wake flow are investigated using iso-Q/λ2 surfaces, vorticity contours, streamline plots. Three different vortex shedding regimes have been investigated based on values of Reynolds number and shear intensity, viz. steady flow, symmetric and asymmetric modes of vortex shedding. Transition in vortex shedding modes with change in shear intensity has been illustrated with the help of snapshot based technique, named ‘Dynamic Mode Decomposition’ (DMD). Spatial variation of DMD modes for symmetric and asymmetric vortex shedding has been illustrated corresponding to dominant Ritz values. Hilbert Huang transformation (HHT) has been used to decompose complex nonlinear and nonstationary time signal in the wake into different components of varying frequency and amplitude over time. The qualitative aspect of wake nonlinearity is presented with the help of Hilbert and marginal spectra. Nonlinear fluctuations in the wake is quantified in terms of degree of stationarity. Periodic and aperiodic nature of wake flow are analyzed using time delay reconstruction technique and considering Poincare sections in the phase space. Recurrence analysis has been used to examine periodic/ aperiodic wake oscillations using transverse velocity signal. Furthermore, various quantification estimates such as recurrence rate, average length of diagonal line, entropy of diagonal line, trapping time and length of longest vertical line are computed and presented for the different values of Reynolds number and shear intensity considered in present investigation. Nonstationarity and level of synchronous in the wake behavior have been examined using cross-recurrence analysis (CRA).