Numerical Study on Drag Reduction for Grid-Fin Configurations

A grid fin, or lattice fin, consists of an outer frame supporting an inner grid of intersecting planar surfaces of small chord. At transonic Mach numbers normal shocks form at the back of the lattice cells thus choking the flow through the cells and causing a significant increase in drag force. In order to reduce the transonic flow choking, an improved, sweptback grid fin configuration is proposed in the present study. Viscous computational fluid dynamic (CFD) simulations were performed to investigate the flow characteristics of a vehicle with baseline and sweptback grid fins at transonic and supersonic Mach numbers in the range 0.817- 2.0, at zero angle of attack. Good agreement (within the error of 4%) is observed for the computed drag coefficients with data available in literature. The present numerical results indicate the sweptback grid fins reduce the flow chocking. This translates in a grid-fin drag reduction of about 12% for all the Mach numbers investigated in the present study.