In recent years, methane has attracted attention as a propellant for liquid rocket engines because of its various advantages compared to typical propellants such as hydrogen. When methane is used as a coolant for a regenerative cooling system, its near-critical thermodynamic and transport properties experience large variations because its critical pressure is higher than that of typical propellants; this significantly influences the flowfield and heat transfer characteristics. Therefore, adequate understanding of the flowfield and heat transfer characteristics of methane in regenerative cooling channels is a prerequisite for future engine development. In this study, conjugated coolant and heat transfer simulations were performed to investigate the flowfield and heat transfer characteristics of transcritical methane flows in a sub-scale methane-cooled thrust chamber. The computed results were validated against experimental data measured in hot firing tests. They compared well with the measured pressures and temperatures in cooling channels, and wall temperatures were within the permitted levels.
Detailed flow analysis revealed peculiar flow structures in the cooling channel: a strong secondary flow induced in the concave-heated part in the channel throat section and the coexistence of two different gas phases-ideal and real-in a single cross-section in the cylindrical region. A high wall temperature appeared in the cylindrical region of the thrust chamber under the considered conditions; this was due to the heat transfer deterioration induced by an M-shaped velocity profile and a turbulentheat flux reduction. Nomenclature a, b, = coefficients in cubic-type equation of state C p = constant pressure heat capacity G = mass flow rate H = channel height h = heat transfer coefficient Pr = Prandtl number p = pressure q = heat flux R = gas constant Re = Reynolds number R u = universal gas constant s = normal distance T = temperature u = streamwise velocity W = molecular weight x, y, z = coordinate system Z = compressibility factor y + = normalized wall distance 2 = thermal conductivity = viscosity = density Subscripts b = bulk c = coolant cr = critical cw = coolant-side wall gw = hot-gas-side wall in = inlet out = outlet t = turbulent throat = throat pcr = pseudo-critical w = wall
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