Numerical Study on Mechanism of Drag Reduction by Microblowing Technique on Supercritical Airfoil

Numerical studies on the applications of the microblowing technique (MBT) on a supercritical airfoil are performed based on a microporous wall model (MPWM) to represent the macroscaled collective characteristics of the huge number of microjets. The influences on the aerodynamic characteristics by microblowing with a MBT zone on different locations are analyzed. It is found that a MBT zone near the leading edge of the airfoil could achieve more reduction of skin-friction drag than a zone near the trailing edge. While for pressure drag, microblowing does not always result in a pressure drag penalty but could even reduce the pressure drag if the MBT porous zone is arranged on the region near the trailing edge. For the flow field without a shock wave, the MBT zone should be arranged on the lower wall and near the trailing edge. The typical configuration followed this guideline could simultaneously decrease the pressure drag and skin-friction drag while also increasing the lift. Numerical results indicate that a 12.8-16.8% reduction of total drag and 14.7-17.8% increase of lift could be achieved by this typical configuration with a blowing fraction 0.05. However, for the flow field with a shock wave on the upper wall, the performance of the microblowing is obviously suppressed by the existence of the shock wave. (C) 2016 American Society of Civil Engineers.