Effect of Unmixedness in Large Eddies on Ignition and Combustion of Turbulent Jets of the Fuel in a Supersonic Flow

A method and results of computing the influence of unmixedness in large eddies generated by instability of a contact discontinuity on ignition and combustion of turbulent jets of a fuel in a supersonic flow are presented. The basic system of equations is the Reynolds-averaged Navier-Stokes equations. The influence of unmixedness on chemical reaction rates is reproduced by using a random number generator adjusted in accordance with the probability of origination of favorable conditions for proceeding of chemical reactions, which is computed in each node of the computational grid. The problem of combustion of a plane hydrogen jet injected into a supersonic flow along the plate surface is considered as an example. It is shown that allowance for unmixedness in the case where the flow and the jet have favorable initial parameters for self-ignition leads to a delay in heat release and to origination of pressure and temperature fluctuations. As the parameters approach the self-ignition limit, these fluctuations increase, and the combustion becomes intermittent. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 1, pp. 49–56, January–February, 2006.