Modelling of Stratification in Cooling Channels and its Implementation in a Transient System Analysis Tool

The use of system modelling tools for transient analysis of LRE is becoming more and more common since their accuracy is constantly improving. But the design and analysis of regeneratively cooled walls of cryogenic thrust chambers is still a challenging problem. Conventional one-dimensional calculation methods assume an ideal mixing of the thermal energy into the fluid cell, therefore in case of cooling channels with high aspect ratio a significant error will arise on the fluid to wall heat exchange because thermal stratification effects are not taken into account in the fluid flow formulation. EcosimPro is an object oriented tool capable of modelling various kinds of dynamic systems. The model described within this paper is implemented alongside ESPSS, the propulsion system library compatible with EcosimPro. This paper covers a new simplified “Quasi-2D” approach to study the coupled problem of coolant flow and wall structure heat transfer in the cooling channels of a liquid rocket engine from a system point of view. With this approach it is possible to have a fast prediction of the evolution in space and time of both coolant and wall temperature distribution. Unlike the previous models used to evaluate thermal stratification, this one is based on 1D unsteady mass governing equation, and “Quasi-2D” momentum and energy conservation equations. For each longitudinal node, the channel is divided into slices. The governing equations take into account the shear stresses between the slices and the heat fluxes in vertical direction due to turbulent mixing. The model hereafter described can be easily embedded in an unsteady propulsion system analysis for simulating the ignition transient. The code flexibility allows for using the same model also for performance analysis in steady-state, and for off-design studies. Numerical test cases from the University of Rome, and experimental test cases from the German Aerospace Center (DLR) will be simulated and their results will be compared with the simulation results of the model.