A numerical study on dynamic flow past two tandem porous circular cylinders near a moving wall at Reynolds number of 150

Abstract

This study introduces the first comprehensive numerical analysis of dynamic flows past two tandem porous circular cylinders positioned near a moving wall, using lattice Boltzmann method integrated with block-structured topology-confined mesh refinement. Simulations are conducted in wide parameter space of spacing ratios $L/D=1.5-10$, gap ratios $G/D=0.6-5$, and porosities $\varepsilon =10^{-4}-0.8$ at Reynolds number of 150 (where $L,G$ and $D$ are two cylinder’s spacing, cylinder-wall gap and cylinder diameter, respectively). Five distinct flow regimes are identified as overshoot (OS), pairwise (PW) reattachment (CR-continuous reattachment and AR-alternative reattachment), quasi-coshedding (QS), and co-shedding (CS), driven by the variation of porosity, spacing, and gap ratios. Wake transitions reveal complex flow dynamics, with the OS regime marked by shear-boundary layer interactions, CR and AR regimes exhibiting primary vortex shedding, and QS and CS regimes displaying primary, two-layered and secondary vortex shedding modes. Flow transitions diminish at small gap ratios, while at moderate spacing ratios, four regimes of PW, CR, AR, and CS occur, with QS and CS interchanging at large spacing ratios. Hydrodynamically, upstream cylinder fully shadows downstream one near moving wall. The upstream cylinder’s drag coefficient changes inversely related to the downstream cylinder’s. The moderate gap ratio induces dominant Karman vortex shedding behind the downstream cylinder. The porosity coefficient significantly influences the vortex shedding frequency for two cylinders at moderate spacing and gap ratios.