Pressure and geometry scaling of gaseous hydrogen/gaseous oxygen shear-coaxial injectors

The effects of pressure and geometry scaling on the flow and combustion characteristics of gas-gas injectors have been studied both numerically and experimentally. The chamber operating conditions cover a pressure range of 0.1-10 MPa, and the length varies from 0.125 to 0.25 m. The large-eddy simulation technique is used to achieve turbulence closure. Simulations of both pure mixing and combustion in model and prototype combustors at two different pressures are conducted to examine the flow, mixing, and combustion similarities for both the pressure and geometry scaling. Then hot-firing tests covering a pressure range of 0.92-6.1 MPa are conducted to measure the wall temperature. The temperature-increase profile indicates that all the combustion cases are similar. Finally the geometry scaling is also investigated experimentally with two geometrically similar combustors. Results show that similar temperature-increase profiles were obtained for the two combustors. Results of both numerical calculations and experimental measurements suggest that there are similarities of mixing and combustion flowfields for different chamber pressures and geometries when the injection and geometry conditions satisfy the given criteria, i.e., the injection temperature, velocity, and mixture ratio are fixed, gaseous hydrogen/gaseous oxygen shear coaxial injection, and the injector and combustor are geometrically similar.