Experimental Studies in LENS I and X to Evaluate Real Gas Effects on Hypevelocity Vehicle Performance

Abstract

An experimental program combined with numerical analysis has been conducted to examine real gas effects on the performance of hypervelocity re-entry vehicles. These studies which were conducted in the LENS I Shock Tunnel and LENS X Expansion Tunnel examine the flows over simple nose shapes and the Apollo, Mars Lander and Space Shuttle configurations. Measurements were made in air, nitrogen and CO2 at enthalpy levels from 2 MJ/kg to 12 MJ/kg to evaluate the nonequilibrium characteristics of the flow in the test facilities. The laser diode measurements which were made to determine the velocity and NO species concentration in the facility for the full range of enthalpies were in excellent agreement with predictions of freestream velocity but indicated NO mole fractions half of the predicted values. Measurements with the Apollo configuration in the LENS I Shock Tunnel and LENS X Expansion Tunnel were in good agreement with each other and with predictions of shock layer geometry. However, in the higher enthalpy flows, the heating levels were poorly predicted. Measurements in the two facilities with the Mars Lander configuration and CO2 as a test gas demonstrated that in high enthalpy flows there are significant differences in the standoff distances which are believed to result from a nonequilibrium nature of the CO2 flow in the shock tunnel. The measurements in the LENS X tunnel were in excellent agreement with DPLR predictions of the shock shape and standoff distance. Studies were also conducted to examine real gas effects on the control surface characteristics of a shuttle configuration. These studies which were conducted in air and nitrogen in the LENS I Shock Tunnel showed that real gas effects reduced the scale of the separated interaction region over the flap increasing its effectiveness. However, real gas effects reduce the pressure over the curved surface of the wing resulting in a reduced pitching moment and net reduction in vehicle stability.