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978-3-8439-0023-2, Reihe Thermodynamik
A Contribution to Transpiration Cooling for Aerospace Applications Using CMC Walls
170 Seiten, Dissertation Universität Stuttgart (2011), Softcover, A5
For faster and more efficient air transportation systems sustained hypersonic flight offers a great potential. One possibility is to use scramjet (supersonic combustion ramjet) propelled airbreathing space planes because this propulsion system can be very efficient at very high flight Mach numbers.
Currently, several research programs are ongoing investigating the technological foundations in this area. The work presented here focusses on the transpiration cooling technique applied to porous CMC (ceramic matrix composite) materials, which offer a great potential for the use in aerospace applications. The aim was to identify the cooling mechanisms involved and verify and extend models describing these phenomena, which can be found in literature.
For this, an experimental study was carried out using the hot-gas flow facility available at the ITLR (Institute of Aerospace Thermodynamics of the Universität Stuttgart) and several porous carbon/carbon CMC samples provided by the DLR (German Aerospace Center) were investigated with respect to their cooling efficiency.
First, the material was characterized with respect to their outflow and through-flow behavior in separate test setups. Then, these samples were exposed to heated supersonic and subsonic flows generating different heat loads. Since the models available in literature were not capable of representing the specific thermal phenomena in our test setup, they had to be extended. This was verified by a number of transpiration cooling experiments at different temperature levels and heat loads. With the help of this model, transpiration cooling prediction in aerospace (testing) application within non-adiabatic environment is possible when knowing the main-stream conditions.
As a last step, the model for the cooling efficiency was coupled with an extended model for the through-flow behavior. This was also verified using the available experimental data. Now, only the main-stream conditions and the coolant properties need to be known. Then, this model was used to give an estimate of the coolant mass-flow rate and the supply pressure drop for several aerospace application related combustion chambers. It was shown that it is possible to use transpiration cooling with hydrogen as a coolant in high-temperature and high-pressure environments given the availability of a suitable wall material allowing reasonable supply pressure levels at the required coolant mass-flow rates.