Interference and ground effects on flow past two inclined flat plates in tandem arrangement

Direct Numerical Simulation (DNS) was conducted on the flow past two tandem inclined flat plates at a Reynolds number of 150. With an inclined angle θ  = 25°, the high-order spectral-element method is employed for higher accuracy. Fluid force, power spectral density analysis, flow structures, and instability have been investigated focusing on both interference and ground effects. Relative magnitudes of gap spacing “ X ” and plate height “ G ” over plate length “ L ” are investigated with ranges: X/L  = 1–6 at an interval of 1, G/L  = 0.2 to 1.6 at an interval of 0.2. It was found that two asymmetrical vortices formed behind the upstream plate (UP), and then directly reattached to the downstream plate (DP), where larger ratios of X/L and G/L enhanced the vortex shedding behind the plates and magnify the fluid forces. A small gap spacing X/L was found not sufficient to develop the gap flow, where tandem plates were considered as a single body of vortex shedding. With G/L lower than 0.5, the vorticity generated at the trailing edge was gradually neutralized by the boundary shear layer which contributes to lower fluid force. Moreover, the instability of tandem plates was governed by the gap spacing ratio.