The HYPROB Program, developed by the Italian Aerospace Research Centre, aims at increasing system design and manufacturing capabilities on liquid oxygen-methane rocket engines. In this view, it is foreseen to design, manufacture and test a ground engine demonstrator of three tons thrust. The demonstrator baseline concept is regeneratively cooled by using liquid methane. The cooling system is made up by a cooling jacket, having a counter-flow architecture and 96 narrow axial channels, surrounding the thrust chamber. Since the engine is regeneratively cooled, the propellant, such as methane, enters the channels in the nozzle region in supercritical liquid condition; then, it is heated by the combustion gases along the cooling jacket, undergoing a "pseudo-phase" change. At the end of the jacket, methane is collected in the outlet manifold; finally, it is injected by the injector head into the combustion chamber as a supercritical gas and after the mixing with the oxidizer burns at high pressure. The goal of the paper is to describe the activities supporting the cooling jacket design, aiming at identifying the optimal configuration of the cooling channels. However, because in the cooling system, a "pseudo-phase change" of the propellant/refrigerant occurs, the transcritical behaviour of methane has been experimentally and numerically analysed by means of a specific breadboard, called MTP-BB (Methane Thermal Properties Breadboard). MTP results have been used to conduct the validation of the 3-D CFD models, adopted to support the design of the demonstrator cooling system. Several analyses were performed on different cooling channel arrangements, in terms of channel height and rib width. Moreover, simulations described the thermo-fluid dynamic behavior of methane by means of NIST real gas modelling and they were necessary to give the proper input to the thermo-structural analyses in order to verify the most critical sections of the cooling jacket.
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