Effect of Hemispherical Protuberance on the Leading-Edge to Control the Laminar Separation Bubble

Abstract

The excitation of a laminar separation bubble (LSB) under the influence of a hemispherical protuberance has been discussed here. The experiments were conducted over a modeled aerofoil of constant thickness with a semi-circular leading-edge at a Reynolds number (Re) of 1.6 × 105, where freestream turbulence (fst) is 1.2%. A protuberance of height, k = 3 mm is placed at an angle of 60 from the theoretical stagnation point. The characteristic Re based on the diameter of the element and freestream velocity is 1442. The protuberance sheds streamwise vortices leading to an unsteady flow near the leading edge, resulting in a reduction of bubble length by 31–78%. Further, the separation bubble length, its fundamental shedding frequency, and the turbulence statistics become highly asymmetric in the spanwise direction, while the influence of protuberance is felt up to 6k.