Numerical Investigation on the Effect of Leading-Edge Tubercles on the Laminar Separation Bubble

Abstract

The effect of leading-edge tubercles on the aerodynamic performance of E216 airfoil is studied by steady 3D numerical simulations using Transition γ−Reθ turbulance model. The investigation is carried out for the various angles of attack in the pre-stall region at Reynolds number of 100,000. Various tubercle configurations with different combinations of amplitude ranging from 2 mm to 8 mm and wavelength varying from 15.5mm to 62 mm are studied. The effect of tubercle parameters on the laminar separation bubble (LSB) is extensively studied. Improvement in the coefficient of lift (Cl) is observed for most of the tubercled models and is significant at high angles of attack. But the simultaneous increase in the drag coefficient resulted in a marginal improvement in the coefficient of lift to drag ratio (Cl/Cd) for most of the cases except for A2W62, which produced a peak value of 46.91 at AOA 6◦ which is higher than that for the baseline by 7.37%. Compared to the baseline, the magnitude of suction peak is higher along the trough and lower along the peak. The low amplitude and low wavelength tubercle model exhibited smooth surface pressure coefficient (Cp) distribution without any sign of strong LSB formation. The LSB moves upstream with the increase in amplitude and wavelength. The LSB along the trough is formed ahead of that at peak inducing three-dimensional wavy shaped LSB unlike the straight LSB as in baseline. Two pairs of counter rotating vortices are formed on the airfoil surface between the adjacent peaks at two different chord-wise locations which strongly alter the flow pattern over it.

Keywords

• airfoil
• laminar separation bubble
• small scale wind turbine
• tubercle
• turbulent flow