Mitigation of Laminar Separation Bubble Through Leading-Edge Modification of an Aerofoil With Herringbone Riblets

The present study describes the potential of a passive technique involving the leading-edge modification using herringbone riblets with a triangular cross-section in mitigating the leading-edge separation at various angles of attack (α). Pressure and instantaneous flow measurements by hotwire were performed over a semicircular leading-edge aerofoil for α — 0°, 3° and 5° with and without leading-edge modification. The Reynolds number (Re), based on the chord length and the inlet freestream velocity, was 1.6 × 105, where freestream turbulence (fst) being 1.2%. A laminar separation bubble is witnessed on the hydrodynamically smooth leading-edge aerofoil at all α where the transition is governed by inviscid instability. Leading-edge modification with herringbone riblets induced higher turbulence in proximity to the wall, resulting in an earlier transition of the shear layer and a reduction in bubble length by 36–20% for α = 0–5° along with a change in the transition mechanism. In brief, herringbone riblets show promising results in reducing the leading-edge separation.