Effect of Planar Member Cross-Section on Cascade Fin Aerodynamics

Abstract

Grid fins are unconventional control and lifting surfaces consisting of an outer frame supporting an inner grid of small chord intersecting planar surfaces. Credited for their enhanced lifting characteristics at high angles of attack and wider Mach number regimes, minuscule hinge moments, and increased drag, these have been used in numerous aerospace applications. Removal of their cross-members leads to its simplified variant called cascade fins. The present study carries out numerous viscous computational fluid dynamics simulations at subsonic speed and high angles of attack to investigate and compare the impact of the horizontal planar member cross-sectional shape on cascade fin aerodynamics by elucidating the effects of using a NACA 0012 airfoil cross-section instead of a rectangular cross-section and varying the gap between their members. Appreciably higher aerodynamic efficiency attributed to drag reduction and comparable lifting characteristics along with steeper and hastened stall characteristics was deciphered for airfoil cascades. It was also found that optimally reducing the gap alleviates the stall tendency. These trends were further explained using pressure distribution plots and flow visualization analysis for the respective variant. Thus, planar member cross-section and gap selection should be done based on the aerodynamic efficiency requirement, desired maneuverability, and manufacturing cost.