Investigation on the Effects of Atwood Number on the Combustion Performance of Hydrogen-Oxygen Supersonic Mixing Layer

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Combustion enhancement strategies are needed to improve the combustion efficiency of the supersonic shear layer. A 2D hydrogen-air supersonic shear layer with central jet filled of hydrogen and inert gas mixture under different Atwood (At) numbers is simulated, based on Navier-Stokes equations. The main purpose is to study whether optimal combustion enhancement can be obtained by changing fluid properties (At number). The Euler method cannot effectively identify the hidden flow field structure. Thus, the Lagrangian coherent structure method (LCS) is adopted to visualize the evolution process of vortex. Different Atwood numbers are adjusted by different inert gas (\(\mathrm {N}_{2}\), \(\mathrm {Ar}\), and \(\mathrm {He}\), corresponding to At = 0.14, 0.26, 0.57) with identical mass flow of hydrogen. The obtained results show that combustion efficiency of the reacting cases tends to increase and then decrease, as At number increases. At = 0.26 has the best combustion efficiency which is mainly measured by the normalized mass production of water. Combustion efficiency of At = 0.26 is higher than that of other two cases because of the shorter vortex shedding distance and resulting larger burning area. Combustion performance is controlled by the mixing process. Vortex shedding position is found to play an important role in entrainment process which directly decides the combustion efficiency. The entrained oxygen can be completely consumed because of the excess hydrogen. In conclusion, shortening vortex shedding position helps improve mixing and combustion efficiency, which can be achieved by adjusting Atwood Number.