Effect of pulsatile inflow on wake and dynamic characteristics of surface-mounted stepped circular cylinder

Abstract Three-dimensional numerical investigations have been carried out to study the flow past a surface-mounted stepped circular cylinder using commercial software ANSYS Fluent 2023 R2. Pulsatile flow has been imposed at inlet, with amplitude of oscillating velocity component ( α ) taking five values, viz., 0, 0.05, 0.10, 0.15 and 0.20. The Reynolds number ( Re ) and aspect ratio ( AR ) are kept fixed at 200 and 5.0, respectively. Four different values of diameter ratio ( DR = d/D ) are considered, viz., <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mfrac> <mml:mn>1</mml:mn> <mml:mrow> <mml:mrow> <mml:msup> <mml:mn>2</mml:mn> <mml:mrow> <mml:mn>1</mml:mn> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:mrow> </mml:mfrac> </mml:mrow> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mfrac> <mml:mn>1</mml:mn> <mml:mrow> <mml:mrow> <mml:msup> <mml:mn>2</mml:mn> <mml:mrow> <mml:mn>1</mml:mn> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:mrow> </mml:mfrac> </mml:mrow> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mfrac> <mml:mn>1</mml:mn> <mml:mrow> <mml:mrow> <mml:msup> <mml:mn>2</mml:mn> <mml:mrow> <mml:mn>3</mml:mn> <mml:mrow> <mml:mo>/</mml:mo> </mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:mrow> </mml:mfrac> </mml:mrow> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mfrac> <mml:mn>1</mml:mn> <mml:mn>2</mml:mn> </mml:mfrac> </mml:mrow> </mml:math> , for given height ratio ( HR = h/H , ratio of reduced section height to total height). The influence of pulsatile inflow on wake structure is studied using iso-Q surfaces that can predict any variation in size and shape of hairpin vortices. Effect of DR and α on unsteady wake characteristics has been analyzed with the help of Hilbert spectra, based on the time series of lift ( Cl ) signal. Moreover, the marginal spectra of the lift ( Cl ) signal are used to examine the associated spectral energy distribution. In addition, variations of mean drag ( Cd mean ) and root mean square lift coefficients ( Cl rms ) are also studied. Finally, the modes of coherent wake structure have been predicted using dynamic mode decomposition, for varying α .