Numerical investigation on the supersonic hydrogen jet flame affected by shocks

A supersonic jet flame formed by a 2.0 Ma hydrogen jet and a 1.9 Ma heated co-flow air is analyzed in the present study by addressing compressibility effects with consideration of shocks in supersonic flows. The computations make use of a large eddy simulation together with a 19-step H₂/air reaction mechanism. The global features of the flame and the complex wave patterns are discussed. The convective Mach number and Slessor number are used to parameterize the compressibility of the supersonic shear layer. The heat release rate linked with temperature is analyzed in a new space that is based on the mixture fraction and compressing/expanding power rate. It is found that the waves in the chamber make the compressibility indexes decrease significantly, which is an important aspect of the physics for the development of the supersonic mixing layer. When the shocks interact with the shear layer and intersect on the axis forming the so-called cross-shocks, they induce various vortices that promote molecular mixing and vigorous combustion. This is good for ignition and flame stabilization since the heat release rate is enhanced significantly. Besides, the local explosion releases a lot of heat and contributes to fluid expansion. Although shocks are associated with compression, local low-pressure expansion zones could be observed behind the cross-shocks closely due to heat release, and the local explosion reinforces the shocks with a bigger wave angle.