Flow control of diamond-shaped cylinders with slots at Re=150

This study presents a comprehensive numerical investigation of passive flow control around diamond cylinders with horizontal and vertical slots at a Reynolds number (Re) of 150. Using a numerical framework, it is systematically analyzed the effects of slot orientation (horizontal and vertical) and width ratio (s/D ranging from 0.05 to 0.30) on the wake dynamics. Results demonstrate that the slot orientation fundamentally determines the flow control mechanism. Horizontal slots progressively extend the vortex formation length and weaken vortex shedding intensity, ultimately achieving complete suppression of periodic shedding at s/D = 0.30, reducing drag by 37%, and eliminating fluctuating forces. In contrast, vertical slots maintain the fundamental wake structure while attenuating vortex strength, achieving a superior 50% drag reduction at s/D = 0.30 without suppressing periodicity. Pressure distribution analysis reveals that horizontal slots primarily modify base pressure through direct wake interaction, while vertical slots enhance pressure recovery without significantly altering separation characteristics. Proper orthogonal decomposition results confirm that the distinct physical mechanisms of horizontal slots redistribution of the energy between coherent modes before stabilizing the wake, while vertical slots preserve the modal structure while systematically reducing fluctuation energy. Time-averaged streamline topology reveals formation of additional focal structures in horizontal configurations, contrasting with persistent sub-wake patterns in vertical arrangements. These findings elucidate the underlying physics of passive flow control and provide crucial design guidelines for engineering applications requiring either maximum drag reduction (vertical slots) or elimination of flow fluctuations (horizontal slots) in diamond-shaped cylinders at low Reynolds numbers.