Experimental and Numerical Investigation of Bio-Inspired Riblet for Drag Reduction

Abstract

Flow alteration using the bio-inspired riblet structure is a fascinating field of study resulting in drag benefits. Riblets have no power requirement being a passive method. This work aims to study the effect of riblets on flow and drag behavior using both experimental and numerical analysis. The experiments are performed using a flush mount shear stress probe (FMSSP) and constant temperature anemometry (CTA). FMSSP is a novel technique to measure stress without obstructing the flow. The study is done on longitudinal streamwise sawtooth-shaped riblet with a maximum Reynolds number (Re) of 1.68 × 105. Three-dimensional numerical modeling of the riblet structure over a smooth wall is analyzed to study the mechanism responsible for drag-reducing behavior. A maximum reduction of 13.2% in shear stress is observed in the study. The result infers an upward shift in the velocity profile relative to the smooth wall in the near-wall region. Due to riblets, large-scale structures breakdown near the wall and better mixing are observed above the surface. Near-wall vortices are imparted a movement away from the wall due to the riblet tip, thus mitigating the near-wall fluctuations. Along with this, drag-reducing riblets hamper the cross-flow near the wall, thus further decreasing the turbulence intensity. Results suggest that turbulent kinetic energy (TKE) has a similar trend to the drag reduction characteristic near the wall. The finding ascertains the potential application of the riblets for real-life settings.