Design of Stream Thrust Probes in Reacting Flows

Abstract

Pitot pressure may be used as a measure of stream thrust in supersonic reacting flows. Previous work has assumed ideal, perfect gas behavior. This paper extends the analysis to chemically reacting flow. The effect of probe size on the measured pitot pressure is explored. Large probe sizes produce higher pitot pressure than smaller probes. However, even the largest probe sizes do not approach the chemical equilibrium pitot pressure limit because of entropy generation behind the shock attributable to finite-rate chemical reactions. Small probe sizes do approach the frozen chemistry pitot pressure limit. The frozen and equilibrium limits are separated by approximately 10 percent, but the pitot pressures computed with finite-rate chemistry varies less than 3 percent regardless of probe size. This reduces the uncertainty associated with inferring stream thrust from pitot pressure measurements in reacting flows. Conditions typical of a typical storable propellant rocket are considered. These calculations will guide the choice of probe sizes in reacting flows, and provide an indication of the uncertainty associated with inferring stream thrust from pitot pressure in reacting flows.