Control of flow separation using biomimetic shark scales with fixed tilt angles

Sharks can swim with excellent hydrodynamic performance under a variety of flow conditions. The dermal scales of sharks, which can change from an aligned state to a tilted state, account for flow control in the attached and separated flow. However, the mechanism of using tilted biomimetic shark scales for flow separation control is still not clear. In the present work, the effects of biomimetic shark scales with fixed tilt angles on flow separation over an inclined plate are investigated experimentally using time-resolved particle image velocimetry. The Reynolds number based on the streamwise length of the plate and the freestream velocity is 2.0 × 104. From the perspective of the time-averaged flow field, it is found that the tilted biomimetic shark scales decrease the reattachment length by 57% when the angle of attack of the plate is 10°. From the perspective of the instantaneous flow field, the shed vortices over the tilted biomimetic shark scales are closer to the wall than those over the flat plate. The fluid convection is strengthened in the separated shear layer by the tilted biomimetic shark scales, as the momentum transportation and the vorticity convection are enhanced. As a result, normal motions of fluid in the separated shear layer are improved, and energy is supplied to resist flow separation. A flow separation control strategy is proposed for different tilt angles of the biomimetic shark scales and angles of attack, which is significant for engineering applications involving flow control.Graphical abstract