Effect of free stream turbulence intensity on corrugated airfoils at ultra low Reynolds numbers

The effect of free stream turbulence on flow around a corrugated airfoil at ultra low Reynolds numbers have been investigated using particle image velocimetry. The experiments are undertaken at Re = 960-11700, Angle of Attack (AoA) = +5°, −5° and Turbulence Intensity (TI) = 6%. The present study is perhaps the first study to explore the effect of free stream turbulence on a corrugated airfoil profile. Interestingly, it is observed that, at lower Reynolds numbers, the vortices in the corrugation valleys result in the formation of virtual airfoil around the corrugated surface. The virtual airfoil pattern is similar to that reported in the literature without the influence of external turbulence. However, at higher Re, the vortices in the corrugation valleys are suppressed due to the combined effect of high inertia force and the turbulence intensity in the flow. In the absence of the virtual airfoil, the close interaction between the flow and corrugation surface is likely to result in reduced aerodynamic efficiency. The observation indicates that the performance of corrugated airfoil under varying Reynolds number regimes is highly sensitive to the turbulence intensity in the flow.