FLUID INJECTED COOLING SYSTEMS FOR HYPERSONIC RE-ENTRY VEHICLES

Abstract

Re-entry into the earth’s atmosphere, or any atmospheric body, is an arduous task. High heat loads, intense deceleration, and chemically reactive flows make this a difficult environment to model and design for. Typically a great deal of foresight is needed as to what the physics of the flow and the trajectory the vehicle will take beforehand. The current state-of-the-art technologies are adequate at handling the thermal and chemical environments found in such flows, but require precise timing and positioning to ensure the vehicle follows a predetermined trajectory with a narrow margin for error. This rapidly becomes problematic for missions when such conditions are not known beforehand or some change is made to the mission profile. For this reason it is novel to have a cooling system that is capable of adapting to changing flight conditions and mission requirements. The purpose of this study is to determine the effectiveness of a Fluid Injection Cooling System (FICS) as a substitute for a standard heat shield on reentry vehicles. The reentry vehicle considered is the Orion Crew Module, part of the Orion Multi-Purpose Crew Vehicle being developed by NASA. The FICS for this study is a single cold-gas injector situated at the stagnation point of the capsule, with Helium and Nitrogen being tested as the injected gasses. The FICS reduces reentry heating through three mechanisms: increasing bow-shock standoff distance, absorbing heat and creating an inert buffer around the capsule. Increasing the standoff distance favorably alters the shock geometry to reduce heat transfer to the capsule. The cool-gas/fluid also absorbs heat from the much hotter external flow. Finally, the inert buffer created by the FICS helps protect the capsule from free radical oxygen molecules which can erode the capsule and interfere with the communication system. This paper investigates the effectiveness of such a system by using computational modeling of the flow in ANSYS FLUENT v.16 with post processing being done in CFD POST v.16 using an axisymmetric model of the re-entry vehicle to reduce computation time and data needs. Data collected in this study is processed by use of non-dimensional parameters so that the results of this study can be used on scaled models for validation and can be applied to a wide range of flow regimes. The procedure of forming non-dimensional parameters will also allow the results of this study to be implemented in control algorithms that could correct for deviations from the planned trajectory.