Flow over an aerofoil without and with a leading-edge slat at a transitional Reynolds number

In this study, a multi-element aerofoil including NACA2415 aerofoil with NACA22 leading-edge slat is experimentally and computationally investigated at a transitional Reynolds number of 2 x 10(5). In the experiment, the single-element aerofoil experiences a laminar separation bubble, and a maximum lift coefficient of 1.3 at a stall angle of attack of 12 degrees is obtained. This flow has been numerically simulated by FLUENT, employing the recently developed, k-k(L)-omega and k-omega shear-stress transport (SST) transition models. Both transition models are shown to accurately predict the location of the experimentally determined separation bubble. Experimental measurements also illustrate that the leading-edge slat significantly delays the stall up to an angle of attack of 20 degrees, with a maximum lift coefficient of 1.9. The fluid dynamics governing this improvement is the elimination of the separation bubble by the injection of high momentum fluid through the slat over the main aerofoil - an efficient means of flow control. Numerical simulations using k-k(L)-omega are shown to accurately predict the lift curve, including stall, but not the complete elimination of the separation bubble. Conversely, the lift curve prediction using the k-omega SST transition model is less successful, but the separation bubble is shown to fully vanish in agreement with the experiment.