Passive Control of Shock Oscillation Around a Biconvex Circular Arc Airfoil in a Channel

Abstract

A strong normal shock wave, generated on an airfoil, is responsible not only for limiting the aerodynamic performance but also for shock induced boundary layer separation. This shock induced boundary layer separation results aerodynamics instabilities (buffet), high cycle fatigue failure (HCF), nonsynchronous vibration (NSV), flutter and so on. In the present study, a numerical computation has been performed to control the unsteady shock oscillation over a 12% biconvex circular arc airfoil in a two dimensional channel. Reynolds averaged Navier-Stokes (RANS) equations with k-ω shear stress transport (SST) two equation turbulence model has been applied for computational analysis. To control the shock oscillation over a biconvex circular arc airfoil (referred as base airfoil), the geometry of the base airfoil has been modified by incorporating a cavity with two openings on both upper and lower surface of the airfoil. The cavity has been incorporated in such a manner that the mean position (along chord length) of the cavity is placed where the RMS of static pressure fluctuation on airfoil surface (for base airfoil) is maximum. The length and depth of the cavities are kept 10% and 2% of the chord length, respectively. The behavior of the shock wave oscillation has been studied for a particular pressure ratio (defined as the ratio of back pressure to inlet total pressure) of 0.69. The present study investigates the shock wave characteristics over (a) airfoil with no cavity (base airfoil) and (b) airfoil with cavity with 60% opening (60% of cavity length is open). The results showed that the incorporation of cavities on airfoil surfaces not only affect the flow field but also change the behaviour in a great extent. For pressure ratio 0.69, the flow field becomes steady for airfoil with cavities while for base airfoil the flow field was unsteady. The results also show that incorporation of a cavity on airfoil surfaces changes the type of shock wave from normal to λ shock wave.