A Design Trade Study Using CFD Modeling of Reaction Jets for Aerodynamic Control

The use of external jets issuing normal to the surface of a body for aerodynamic control has received attention in the past due to experimental observations of favorable interactions between the free stream flow and the jet wake which, in effect, augment the force produced by the jet. The purpose of this study was to perform preliminary trades to determine the effect of variables such as reaction jet location, free stream Mach number, reaction jet stagnation pressure, and reaction jet exit Mach number on augmentation factors for a representative lifting body cruise missile configuration. A computational fluid dynamic analysis, solving the Euler equations, was used to perform the trades listed above. It is shown that the reaction jet augmentation factors are greater, and hence the reaction jet is more effective, at higher free stream dynamic pressures in the subsonic regime. It is also shown that the augmentation factors are essentially independent of reaction jet stagnation pressure for choked nozzles with jet to free stream stagnation pressure ratios between 1.24 and 3.0. Additionally, it is shown that increasing the jet exit Mach number decreases the reaction jet augmentation factor. Finally, the strong influence of reaction jet placement and body geometry on augmentation factors is discussed and the need for this level of analysis is justified.