Modeling of Chemically Reacting Flows from a Side Jet at High Altitudes

The interaction of a jet from a 60-lbf (267-N) thruster positioned on the side of a small rocket, with the rarefied atmosphere between altitudes of 80 to 160 km, is studied numerically. A multistep approach is employed, which combines the successive computation of the flow inside the thruster using a Navier‐Stokes solver, the axisymmetric plume core flow, and chemically reacting three-dimensional plume-atmosphere interaction using the direct simulation Monte Carlo method, and obtains the UV radiation fields based on the flow solution. The impact of the boundary layer inside the nozzle as well as the rocket speed (5‐8 km/s) and flight altitude (80‐160 km) on the plume-atmosphere interaction is examined. I. Introduction A TMOSPHERIC interceptor (AI) vehicles currently being developed use divert and attitude reaction control systems (RCS) to perform quick maneuvers during flight. The forward and aft RCS engines provide the thrust for attitude (rotational) maneuvers (pitch, yaw, and roll) and for small velocity changes along the rocket axis (translation maneuvers). In the past few years extensive experimental and theoretical studies have been undertaken to predict RCS jet interactions with the ambient atmosphere accurately. Although significant progress has been achieved in understanding the phenomenology of the jet-atmosphere interaction, several important problems still need to be resolved, particularly with regard to supersonic and hypersonic flows at low and high altitudes. Experimental measurements have been made to characterize the jet-atmospheric interaction in wind-tunnel facilities. However, it is difficult to scale these results 1 to flight conditions because of freestream/plume chemistry, Reynolds number, surface, and wall interference effects. Computational studies are therefore necessary to supplement and expand experimental efforts and obtain credible information on performance characteristics and flowfield structure of RCS thrusters at different altitudes. At low altitudes (up to about 60 km) the freestream-jet interaction is characterized by thin plume and bow shock waves and a jet-induced separation region in front of the divert thruster side jet. 2 The flow separation is responsible for the elevated pressure in this region and corresponding thrust amplification and might also affect the operation of optical sensors located upstream from the nozzle. 3,4 The problem of sensor contamination was considered in Ref. 5. AI vehicle aerodynamics and thruster performance at low altitudes were examined numerically by several workers, mostly using solutions of the Navier‐Stokes equations. 6−9 The jet-atmosphere interaction at high altitudes is qualitatively different from that at low altitudes. The flow separation in front of the jet becomes less pronounced and diminishes at altitudes 80 km and higher, and the effect of the atmosphere on the plume is much weaker. Because of the rarefaction, the jet interaction impact on the vehicle aerodynamics is significantly smaller. The direct simulation Monte Carlo (DSMC) method was used in Ref. 10 to compute the three-dimensional jet interaction for a corner flow configuration,