Passive Shock Wave/boundary Layer Control for Transonic Supercritical Airfoil Drag Reduction

Download or read book Passive Shock Wave/boundary Layer Control for Transonic Supercritical Airfoil Drag Reduction written by Lakhdar Bahi and published by . This book was released on 2013 with total page 183 pages. Available in PDF, EPUB and Kindle. Book excerpt: An investigation of the passive shock wave/boundary layer interaction control aiming at reducing the drag for conventional and supercritical airfoils at transonic Mach numbers is presented. A 3x 15.4-inch Transonic Wind Tunnel was designed, constructed and calibrated to achieve this objective. Modifications were made in the initial constant area test section to accommodate for the boundary layer growth along the tunnel walls. The boundary layer of the test section bottom wall was removed via a bleed system, so that the new boundary layer began at the airfoil leading-edge stagnation point. A variable porosity test section top wall was used to minimize the wall interference. A manometer board and a Schlieren system were constructed to measure the pressures and obtain Schlieren photographs of the flow field over the different airfoils in the test section. The passive drag control concept, consisting of a porous surface with a cavity beneath it, was investigated with a 12-percent-thick circular arc and a 14-percent-thick supercritical airfoil mounted on the test section bottom wall. The porous surface was positioned in the shock wave/boundary layer interaction region. The flow circulating through the porous surface, from the downstream to the upstream of the terminating shock wave location, produced a lambda shock wave system and a pressure decrease in the downstream region minimizing the flow separation. The wake impact pressure data showed an appreciably drag reduction with the porous surface at transonic speeds. To determine the optimum size of porosity and cavity, tunnel tests were conducted with different airfoil porosities, cavities and flow Mach numbers. A higher drag reduction was obtained by the 2.5 percent porosity and the 1/4-inch deep cavity.