Integrated Analysis for the Design of Tps based on Variable Transpiration Cooling for Hypersonic Cruise Vehicles

Abstract

The thermal management of hypersonic air-breathing vehicles presents formidable challenges. Reusable thermal protection systems (TPS) are one of the key technologies that have to be improved in order to usehypersonic vehicles as practical, long-range transportation systems. Both the aerodynamic and the material performances are strongly related to the near-wall effects. The viscous dissipation within the hypersonic boundary layer, coupled with the high dynamic pressure flight trajectories, generates surface temperaturesfor which the strength and the environmental durabilityof the material can be widely exceeded.In this type of environment,active cooling systems have to be considered in order to afford long duration flights inhypersonicregime. Transpiration cooling represents apromising technique in terms of temperature reduction and coolant mass saving.In order to explore the potentialof this technique, it is important to understand the physics that characterize the boundarylayerand its interaction with the vehicle-s surface. The integrated analysis of the hypersonic boundary layer coupled with the thermal response of a porous mediumis performed here for aflat plate and a2-D blunt bodyconfiguration. A constant value of thetransversal wall velocity is used to simulate uniformtranspiration. A saw-tooth wall velocity distribution is used to simulatethe variable transpirationstrategy. An equalamount of coolantusage has been imposed in order to compare the cooling effectivenessin the two cases. The uniformtranspiration allows areduction of 49% onthe stagnation point heat flux in comparison with the case without transpiration. The variable transpiration reducesthe stagnation point heat fluxbyan additional7% with respect to the uniformtranspirationcase. The heat fluxes derivedfrom the solution of the hypersonic boundary layeras well as the imposed wall temperature are used to perform an integrated analysisthat includes the porous material.Thetest cases analyzed emphasize the importance of evaluatingthe influence of the material-s thermo-physical properties at the initial design stage.For the flight conditions consideredin this analysis a combination of low materialporosity and high thermal conductivity are necessary to generate the requiredinjection strategy. The integrated analysis is essential for the purpose of establishing the optimum transpiration strategy needed to maintain the surface temperatures in the required range. The change in the transpiration distribution along the vehicle surfaces (variable transpiration) allows to selectively cool down the structure in the regions where the higher heat fluxes are located (i.e. nose, leading edges)and diminishes the amount of requiredcoolant fluid.The transpiration for the blunt body can be limited tothe regionswhere thelocalwall heat flux is greater than or equal toapproximately20% of the stagnation point heat flux. This strategy allows the reduction of the total amount of coolant by 62% for the uniformtranspiration and by 58% for the variable transpiration

Meeting Name

10th International Energy Conversion Engineering Conference (2012: Jul. 30-Aug. 1, Atlanta, GA)

Department(s)

Mechanical and Aerospace Engineering

Document Type

Article - Conference proceedings

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2012 American Institute of Aeronautics and Astronautics (AIAA), All rights reserved.

Publication Date

01 Aug 2012

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