Wall suction & slip effect of spherical-grooved bionic metasurface for controlling the aerodynamic noise

Abstract The wall suction & slip effect of the bionic metasurface with periodic spherical grooves on the vehicle body surface is proposed for aerodynamic noise control, and physical mechanism is investigated by theoretical analysis and simulation. When fluid flows through the grooved vehicle body surface, wall suction effect occurs due to clockwise pressure difference around the interior groove. The trailing vortex region of the vehicle body is reduced, the fluctuating pressure on the wall surface decreases, and the adverse pressure in the boundary layer is relieved. On the other hand, a slip velocity consistent with flow direction is generated at the interface corresponding to grooves, which results in reduced velocity gradient in the boundary layer and decreased thickness of the boundary layer. Ideally, the boundary layer could disappear when the velocity of slippage is increased to that of the flow by adjusting the grooves parameters, such as, the groove depth, pitch, and radius. Overall, the wall suction & slip effect fundamentally prevents generation of the boundary layer and delays its separation. Finally, effective control of aerodynamic noise within 450–1000 Hz on the vehicle body surface is realized by an average drop of 11.97 dB and up to 100% at 500 Hz. This study opens up a possibility for full control of boundary layer and could have effective applications in controlling aerodynamic noise.