Effects of Different Shaped Cavities and Bumps on Flow Structure and Wing Performance

The stall of an aircraft is one of the most dangerous phenomena in the aviation world, resulting in a sudden loss of lift because of boundary layer separation. This work aims to delay separation and to improve wing aerodynamic performances by introducing bumps and cavities on the upper surfaces of the wing. A numerical study on the effects of both cavities and bumps on flow structures and wing aerodynamics of NACA 0012 profile is conducted. The CFX code has been used to perform calculations of steady and uncompressible Reynolds Averaged Naviers-Stokes equations. The airfoil has been exposed to a free stream velocity of 5.616 m/s and chord based Reynolds number of 3.6 x 105 (chord length). A series of test on unmodified airfoil has been carried out for various turbulence models at angles of attack ranging from 0° to 15°. Then, the two-equation k-ω SST (Shear Stress Transport) has been retained for the further cases. Different configurations obtained through a modification of cavities and bumps shape, dimension, and position on the airfoil chord are investigated. Both the shapes considered are semi-spherical and semi-cylindrical, placed at two positions on the airfoil chord. The first location is in suction pick at X/C= 0.3 and the second one is at 0.7. Results show that the application of bumps delays the boundary layer separation and increase drag coefficient. A slight enhancement in lift and drag is observed at angle of attack of 15° for the cases where the cavities are placed at 0.7 m from the leading edge. In addition, calculations show that the stability of the vortex formed inside the cavities depends strongly on their shape and the cylindrical one has better performances.