Visualization of Flowfield Modification by RCS Jets on a Capsule Entry Vehicle

Abstract

Nitric-oxide planar laser-induced fluorescence (NO PLIF) was used to visualize the flow on the aft-body of an entry capsule having an activated reaction control system (RCS) jet. A capsule shape representative of the Apollo command module was tested in the NASA Langley Research Center's 31-Inch Mach 10 wind tunnel facility. Two different RCS converging-diverging nozzle designs were used. One nozzle had a conical diverging section while the other had a bell-shaped contoured section followed by a conical section. The two nozzles had area ratios of 13.4 and 22.5 respectively. Both conical nozzle sections had halfangles of 10˚. Low-and high-Reynolds number cases were investigated by changing the tunnel stagnation pressure from 350 psi to 1300 psi, resulting in freestream Reynolds numbers of 0.55 and 1.8 million per foot respectively. For both cases, three different jet plenum pressures were tested (nominally 56, 250 and 500 psi). Images were also acquired for conditions where the jets were issuing into low pressure static gas with the wind tunnel not operating. A single vehicle angle-of-attack of 24˚ was investigated. Visualizations of the flow issuing from the two nozzle shapes were markedly different near the nozzle internal to the RCS jet plume, while relatively similar in structure on the outer edges of the plume. Visualizations produced by seeding pure NO from the vehicle's forebody show that operation of the RCS jet forces the aft shear layer to become turbulent and deflects the shear layer away from the vehicle significantly, with deflection angle increasing with jet pressure.

Research on RCS Jet Interaction Characteristics of the Capsule Entry Vehicle at Subsonic and Transonic Speed

“…Buck [3] studied the effects of rolling and lateral RCS jet ignition on surface heating, pressure, and flow field structure under different conditions. Danehy [4,5] studied the flow field structure of RCS under different jet pressure and other conditions by PLIF technique. The re-entry stage of the capsule entry vehicle will go through the subtransonic speed, so it has an important engineering background and research value to study the RCS jet interaction characteristics at sub-transonic speed.…”

Comparison of PLIF and CFD Results for the Orion CEV RCS Jets

“…Also compared in Experimental Results and Comparison with CFD is the simplified CFI expression shown in Eq. (10). This expression is a two dimensional polynomial fit for T and P and includes several assumptions.…”