Transpiration cooling in H₂/O₂-combustion devices

The contribution summarizes the experimental and numerical work in the field of transpiration cooling performed at the DLR Research Center Lampoldshausen, Germany. Special emphasis is put on those parts of the work which are oriented towards technological aspects of this cooling technique. A modular GH₂/GO₂-fired model combustor has been equipped with porous wall segments to study the performance of this cooling technique under various operating conditions. For combustion chamber pressures between 0.3 MPa and 1.5 MPa and heat fluxes to the uncooled chamber between 1.5 MW/m² and 8 MW/m², respectively, two different coolants, de-ionized water and gaseous hydrogen, have been applied varying the coolant mass flow rates within at least one order of magnitude. Parallel to the experiments, preliminary numerical work has been carried out which emphasizes the development of the temperature transients inside the porous walls. The experimentally determined Stanton numbers which characterize the heat transfer to the cooled wall vary within 0.002 and 0.008, depending on the operating conditions and thus are in good agreement with the literature [1]. The experimental results achieved so far indicate that the cooling efficiency does not show a monotonous behavior over the entire range of coolant mass flow rates but changes its slope at lower blowing ratios. Although there are different explanations possible, we have not yet enough data available for a final conclusion. Therefore, more basic investigations of near wall phenomena in a blowing boundary layer will be performed in a 2D-channel applying non-intrusive laser-optical diagnostic techniques such as LDA, CARS, and different RAMAN-techniques to receive information about the species concentrations which will allow to determine the spanwise and streamwise stability of the cooling layer. The paper finishes with an outlook on future plans for transpiration cooling at DLR Lampoldshausen.