A Numerical Study Into the Influence of Leading Edge Tubercles on the Aerodynamic Performance of a Highly Cambered High Lift Airfoil Wing at Different Reynolds Numbers

Leading-edge protrusions (tubercles), inspired from the pectoral flippers of the humpback whale, has demonstrated the ability to be an effective passive flow control method for the stall phase of an aerofoil in terms of delaying the stall, gentling it and increasing maximum lift coefficient. While the effect in the pre-stall phase varies depending on the geometrical features of the airfoil as well as the value of Reynolds number (Re). Through the last two decades, many studies have tried to investigate the effects of adapting protrusions on the leading edge of wings for different flow regimes, however there is a little work associated with revealing tubercles performance for the lifting surfaces with highly cambered cross-section, which are commonly used at a wide range of Re due to the variety of applications; vertical axis wind turbines (VAWTs), unmanned air vehicles (UAVs) and cargo airplanes. The present paper aims to investigate the effect of implementing leading edge tubercles on the performance of a rectangular finite span wing with the highly cambered S1223 foil at Re=120,000, Re=270,000 and Re=1,500,000 Numerically using ANSYS Fluent software. besides, illustrating their influence on stall propagation characteristics for a tapered wing at Re=270,000. Four models (rectangular and tapered wing with and without leading-edge tubercles) were built using SOLIDWORKS computer-aided design (CAD) software. The tubercles geometry is defined by three parameters: Amplitude, Wavelength and Phase. For the present work, the amplitude and the wavelength are to be 2.5% and 25% of the local chord respectively with a phase of 0. The steady Reynold’s average Navier-Stokes (RANS) scheme with shear stress transport (SST) K-omega turbulence model has been solved for the computational flow domain that has structured hexahedral elements. The computational fluid dynamics (CFD) model was submitted to independent studies for mesh and domain. Then it has been validated using a previous experimental work. The Lift and drag coefficients have been plotted versus angle of attack (α) at pre- and post-stall for the two rectangular wings at the three values of Re. Moreover, the performance of the models was compared and the stall propagation along the spanwise was monitored for the two tapered wings. The results showed that the modified wing outperforms the unmodified one for the different values of Re. The flow visualization demonstrated the presence of counter-rotating vortex pairs (CVPs) for the case of the modified model which were supposed, by the preceding studies, to be the responsible for delaying flow separation. In addition, tubercles have shown their ability to retard the stall propagation as they divide the flow over the span into segregated sections.