A study on supersonic mixing by circular nozzle with various injection angles for air breathing engine

Abstract

SCRAM-jet engine is considered to be one of the useful system propulsion for super/hypersonic transportation vehicle and various researches were made to develop the engine. However, there are a lot of problems to be solved to develop it and one of them is the problem of supersonic mixing. In the SCRAM-jet engine combustor, main airflow is supersonic and residence time of the air is very short (about 1 ms). Hence rapid mixing of air and fuel is necessary. However, usually it is quite difficult to mix fuel with air in very short distance. Also total pressure loss occurs by flow interaction the air and fuel. Total pressure loss is not preferable because it causes the thrust loss. Therefore, supersonic mixing with very rapid mixing and lower total pressure loss ratio is highly requested. In order to develop the supersonic mixing, it is very important to understand the effect of injection angle. In present study, we investigate the effect of injection angle with circular sonic nozzle by changing the injection angle. Experimental and computational studies on supersonic mixing phenomena of two-dimensional slot injector with various injection angles were conducted. Supersonic wind tunnel was used for the experiments. The free stream Mach number is 3.8, total pressure is 1.1 MPa and total temperature is 287 K on average. As a secondary gas, helium gas was injected at sonic speed from the circular nozzle. The injection angle is 30°, 90° and 150°. Its total pressure is 0.4 MPa and total temperature is 287 K on average. The same flow field was also simulated by solving three-dimensional full Navier–Stokes equation with AUSM-DV scheme [Y. Wada, M.S. Liou, A flux splitting scheme with high-resolution and robustness for discontinuities, AIAA Paper 94–0083, 1994] for convective terms and full implicit LU-ADI factorization method [S. Obayashi, K. Matsushima, K. Fujii, K. Kuwahara, Improvements in efficiency and reliability for Navier–Stokes computations using the LU-ADI factorization algorithm, AIAA Paper 86–0338, 1986] for time integration. Central difference was used for viscous terms and k – ω two-equation turbulence model [D.C. Wilcox, Reassessment of the scale determining equation for advanced turbulent models, J. AIAA 26(11) (1988) 1299–1310; D.C. Wilcox, A two-equation turbulence model for wall-bounded and free-share flows, AIAA Paper 93–2905, 1993] was also employed. In the experiments, stream line on the wall surface was revealed by the oil flow picture and the flow field was visualized by the Shlieren photograph. The wall static pressure profile along the flow was obtained by the wall pressure measurements. Also volume fraction distribution measurements were conducted. Each one of those showed good agreement with computational ones. From the thorough investigation of the flow field by experiments and computations, various characteristics of the supersonic mixing with circular nozzle have been revealed.