Performance of Transpiration-Cooled Heat Shields for Reentry Vehicles

Abstract

This paper presents results of a system study of transpiration cooled thermal protection systems for Earth re-entry. The cooling performance for sustained hypersonic flight and transient re-entry of a blunt cone geometry is assessed. A simplified numerical model is used to calculate the transient temperature of a transpiration cooled heat shield. The performance of transpiration cooling is assessed by calculating the overall required coolant mass for different steady state and transient flight scenarios. Spatially and temporally optimised mass injection is presented for various flight conditions. The majority of the injection is required on the spherical nose segment of the blunted cone. Carbon/Carbon composite ceramic and the ultra high temperature ceramic Zirconium diboride are considered as wall materials. Both materials require similar amounts of coolant injection. In continuous hypersonic cruise, transpiration cooling is highly effective for flight conditions with velocities below 8 km s −1 and altitudes above 40 km. For transient re-entry, transpiration cooling is most viable for trajectories of entry velocities below 8.5 km s −1 and ballistic coefficients below 2.1 kg m −2. Nomenclature A Area, m 2 C D Drag coefficient c p Specific heat capacity, J kg −1 K −1

Numerical Simulation of Transpiration Cooling for a High-Speed Vehicle with Substructure

“…Two high-temperature porous materials are chosen: the main purpose of which is to confirm that the quasi-two-dimensional approach accurately models the transient change in temperature through the material. These are carbon-carbon (C/C) ceramic composite [1] and the ultra-high-temperature ceramic (UHTC) ZrB 2 [17]. The material parameters used in this study are summarized in Table 1 [18,19].…”

“…Figure 14 shows the coolant injection region from s 0 to 0.11 m. This has been chosen based on the conclusions in Ref. [17], which showed for a number of trajectories that transpiration cooling is only needed near the nose to maintain a vehicle below critical temperature limits. The mass flux distribution at the coolant injection region is shaded in Fig.…”

“…This assumption is justified by considering Ref. [17], which showed through a survey of different transpiration cooling experiments that the boundary layer is not tripped if the blowing ratio is kept below 0.04.…”

Plenum Pressure Behavior in Transiently Heat Loaded Transpiration Cooling System

“…One active cooling technology is transpiration cooling, which has expanded its applicability through the development of high temperature porous materials [4][5][6][7][8][9][10]. Examples for transpiration cooling applications are heat shields of reentry vehicles and combustion engines [10][11][12][13][14]. Transpiration cooling means that a gaseous or liquid coolant is fed through the wall, which consists of a porous material, into the hot gas region.…”

Analytical solution of flows in porous media for transpiration cooling applications

“…This is exacerbated for a slender vehicle when the leading edge radius becomes small, as the surface pressure and heat transfer become concentrated on the stagnation point and the downstream flow field will approximate the post-shock state after an oblique shock wave (Lees 1956). This situation requires a spatial distribution of transpired coolant that is higher at the stagnation point and falls off toward the downstream region (Hermann, McGilvray & Naved 2020). Designed distributed blowing is further complicated through the changing external surface pressure, which will impose an internal flow pattern in the porous medium.…”