A contribution to transpiration cooling for rocket combustion chambers in a stacked transpiration cooling arrangement

Abstract

As space enabler, rocket technology is the cornerstone of humankind’s space exploration endeavors. However, the high thermal loads on the propulsion systems and economic cost pressures require efficient cooling mechanisms with durable materials for future reusable space transportation systems. These technical demands are encapsulated by transpiration cooling utilizing state of the art ceramic matrix composite (CMC) materials - modern high-temperature resistant, lightweight fiber ceramics. Despite confirmation of the principle applicability of the cooling technique and materials in rocket engines, a theoretical characterization of the thermophysical mechanisms in an application-oriented stacked combustion chamber setup is remaining. This is where the current thesis contributes by investigating a multi-functional stacked transpiration cooling arrangement of carbon fiber reinforced carbon materials (C/C) as CMC reference material. By means of three complementary test cases a combined experimental and numerical approach is pursued. Experiments are conducted in subsonic flow conditions to characterize a reasonable description of the complex overlapping of the different kinematic and thermal boundary layer situations, to analyze a modeling of the thermal cold-side boundary conditions, and to identify the influence of the wake flow on the superposition capability of a transpiration cooling system. Numerical Reynolds-averaged Navier-Stokes simulations (RANS) applying the in-house OpenFOAM-based simulation tool spectraFOAM complete this holistic approach. As a result, firstly, a suitable characterization of the external boundary layer phenomenology in the mixing zone of the transpiration cooling setup is demonstrated by using the momentum thickness δ2 and enthalpy thickness δh rather than the commonly used running length x. Secondly, an analysis of the overall thermal situation within the porous structure regarding the influence of the cold-side boundary condition on the surface temperatures reveals a good agreement between experimental and numerical data. Thirdly, based on the combination of transpiration cooling and a transpired coolant wake flow, an initial approach on the superposition principle in transpiration cooling has been conducted. A general applicability of the superposition principle in transpiration cooling is proven valid, even though a conclusive recommendation for a cold reference temperature remains pending.