Wake transition of flow past porous D-shaped cylinder near a moving wall

This comprehensive numerical study examines dynamic flow past a permeable D-shaped cylinder near a moving wall in a wide parameter space of porosity (10−4−0.8) and gap ratio (0.6−5) at Reynolds number of 150. Wake dynamics is classified into four regions: overshoot (OS), overshoot with wavy vortex street (PW), primary and meandering vortex street (PM), and co-shedding vortex shedding street (OP). Wake transitions of these regimes are highly switchable in parameter space, where gap ratio variation controls vortex shedding in intermediate and far wake. For small gap ratios, increasing porosity shifts the wake from PW to OS, enhancing shear layer stability. At moderate gap ratios, PM and OP occur, with OP requiring higher porosity due to flow penetration. Pressure coefficient distributions approach a rigid cylinder's as porosity decreases. Stagnation points shift toward the moving wall at small gap ratios but align with an isolated circular cylinder at large gap ratios. Higher porosity shifts stagnation points away from the wall at small gap ratios. Decreasing porosity reduces the time-averaged drag coefficient due to increased permeability. PM and OP regions show higher drag coefficient than OS and PW, exceeding those of single circular and square cylinders due to the moving wall. Lift coefficients approach a single circular cylinder's, except at small gap ratios, where the moving wall effect dominates. At large gap ratios, porosity has a minor effect on the fluctuation of lift coefficient, but a small gap ratio increases the maximum lift coefficient compared to a single circular cylinder.