Thermo-Structural and Thermo-Fluid Dynamics Analyses Supporting the Design of the Cooling System of a Methane Liquid Rocket Engine

Abstract

The HYPROB Program, developed by the Italian Aerospace Research Centre, has the aim to increase the system design and manufacturing capabilities on liquid oxygen-methane rocket engines. It foresees the designing, manufacturing and testing of a ground engine demonstrator of three tons thrust. The demonstrator baseline concept is featured by 18 injectors and it is regeneratively cooled by using liquid methane. In particular, the cooling system is made by a constant number of axial channels and the counter-flow architecture has been chosen; methane enters the channels in the nozzle region in supercritical liquid condition, is heated by the combustion gases along the cooling jacket and then injected into the combustion chamber as a supercritical gas by means of the injection head. The goal of this paper is to describe the thermo-structural and the thermo-fluid dynamic analyses that have been performed in order to support the design activities aiming at identifying the optimal configuration of the cooling jacket in terms of number of channels, rib height and width. In fact, a fully 3-D model, regarding a single channel, heated by the design input heat flux has been considered in order to perform CFD simulations aiming at describing the thermo-fluid dynamic behavior of methane. The results in terms of convective heat transfer coefficients have been taken into account as inputs for the thermo-structural simulations on the most critical sections of the cooling jacket. The thermo-structural activity has been conducted on the demonstrator by means of a Finite Element Method code taking into account the visco-plastic behavior of the adopted materials. In particular, transient thermal analyses and static structural analyses have been performed using ANSYS code on a 2-D model. These analyses have demonstrated that the cooling jacket can withstand the design goal of 5 thermo-mechanical cycles with a safety factor equal to 4 considering a firing time equal to 30 seconds.

Transcritical Behavior of Methane in the Cooling Jacket of a Liquid-Oxygen/Liquid-Methane Rocket-Engine Demonstrator

“…Finally, the coolant comes out from the cooling jacket at conditions typically characterized by both temperature and pressure values higher then critical ones, and according to the cooling-system characteristics, even as a supercritical gas. Then, methane is injected into the combustor chamber by means of the injectors (C) [16,23].…”

“…Finally, the coolant comes out from the cooling jacket at conditions typically characterized by both temperature and pressure values higher then critical ones, and according to the cooling-system characteristics, even as a supercritical gas. Then, methane is injected into the combustor chamber by means of the injectors (C) [16,23]. Hence, the fluid experiences a sort of "pseudo-change" phase, flowing from the inlet towards the outlet section and changing from a liquid-like condition to a vapor-like one [24].…”

Thermostructural Numerical Analysis of the Thrust Chamber of a Liquid Propellant Rocket Engine

“…The thermal and structural boundary conditions are shown in Figure 6 . Coolant bulk temperatures, combustion gases and their respective heat transfer coefficients, which varied along the axis of chamber, were carried out by computational fluid dynamics (CFD) analyses [ 35 , 36 ]. The heat transfer coefficients and bulk temperatures to be applied in the local model thermal analyses, ranged between the dashed lines in Figure 6 b.…”

Thermal analyses supporting the development of a liquid rocket engine

“…For the thrust chamber cooling system, a counter-flow strategy has been chosen: the refrigerant (CH4) enters the inlet fuel manifold (placed on the bottom of Figure 3) in liquid phase (at pressure and temperature, respectively, higher and lower than the critical values); then methane comes in the cooling jacket in the counter-flow direction with respect to the combustion gases. The propellant temperature raises, due to the energy released by combustion gases, and a phase "pseudo-change" occurs; then, methane comes in the fuel dome as a supercritical vapour and finally injected into the chamber through the injectors where mixes liquid oxygen [13]- [15] and burns. The cooling jacket is composed by rectangular-shaped channels, defined in the bottom part by a copper alloy liner, brazed on a close-out of Inconel©.…”

“…The breadboard is made of a copper alloy (depicted in orange in Figure 8) and its thermo-physical properties, evaluated through a specific characterization activity [13], were considered temperature-dependent. Because of the geometric and thermal symmetry, the numerical model contemplated only half channel in order to reduce the computational effort; the top and right surfaces of the breadboard were considered adiabatic while on the bottom wall a constant heat flux was applied.…”