Conjugate Heat Transfer Analysis of the Wall Heat Flux in a Liquid Rocket

Harvazinski, Matthew (AFRL/RQRC)


Liquid rocket engine combustors are a high temperature and high-pressure environment. These conditions can push the limits of material properties and often require sophisticated cooling solutions. The wall heat flux in liquid rocket engines is a critical parameter to the design of the engine and its thermal management. The recent push for reusability puts further constraints on the design of liquid rocket engines by requiring increased service life and a minimization of post-flight inspection and service. Reusability may also place new requirements on analysis tools including thermal fatigue and the interaction between thermal, fluids, and structural elements. This type of analysis will require accurate inputs, which, at a minimum, will include surface temperature and heat flux measurements. The accurate determination of wall heat fluxes and surface temperatures is difficult, both experimentally and computationally. The measurement of the wall heat flux in a liquid rocket engine is difficult to obtain experimentally. Computational tools often utilize an adiabatic thermal boundary condition, which makes the prediction of wall heat flux impossible.

In the present work, we apply an unsteady conjugate heat transfer model, which couples the solid conduction in the wall with the reacting flow in the combustor. The conjugate heat transfer capability was built into a MPI based parallel in-house research code. This capability is applied to two unsteady problems of interest. The first problem of interest is the determination of the wall heat flux in a highly instrumented H2-O2 rocket engine combustor. In this case, the computational results match the experimental results within 4% over a number of operating conditions. The second problem of interest is the analysis of the heat flux of a rocket engine plume impinging a surface. In this setup, the heat flux is computed for multiple different surfaces and compared with average data from experiments. Average results from the simulation are consistent with experimental results. The simulation results provide a greater resolution of the data, including the spatial distribution and surface temperature. This data is highly desirable and is not available in the experiment. In both of these test configurations, the computations are extremely expensive because of the disparate time scales between chemistry, fluid dynamics, and heat transfer.