A numerical study on dynamic flows past three tandem inclined elliptic cylinders near moving wall

Abstract

This numerical study focuses on the dynamic flows past three tandem inclined elliptic cylinders of equal spacing parallel to a moving wall using a lattice Boltzmann method. The gap ratio (G/D=0.6–2.5, where G and D are the gap between the wall surface and cylinder center and major axis, respectively), spacing ratio (L/D=1.5–10, where L is the distance of two adjacent cylinder centers), and inclination angle (α=±15°,±30°,±45°—the angle between normal vector and cylinder's major-axis) are explored at Reynolds number Re = 150 (based on D). The intended analysis links hydrodynamic coefficients, wake structures, and spectral analysis in parameter space of α−G/D−L/D to fluid mechanics. The flow is highly adjustable in this space, dividing into seven regimes: overshoot, continuous reattachment, alternative reattachment, wavy, meandering, quasi-coshedding, and coshedding, which are spatially classified into four modes due to flow interference: shear layer, primary, two-layered, and secondary vortex shedding modes. Transitions between adjacent modes determine three boundaries; and hydrodynamic coefficients differ substantially in parameter space. Due to shadowing, the upstream cylinder has a larger drag coefficient than the middle and downstream cylinders, reducing the drag coefficient of upstream cylinder and the lift coefficient of middle and downstream cylinders. α=±45° has the highest lift oscillation among the three cylinders and a small drag coefficient of the upstream cylinder. The moving wall's proximity effect increases the upstream cylinder's lift coefficient for α<0°, being negligible for high G/D across the full L/D range and stabilizing the lift oscillation of three cylinders.