Analytical study on near-field entrainment in a transient turbulent free jet

摘要

Ignition of a premixed fuel-air mixture by a transient jet or puff of hot gas has multiple applications. The rate of mass entrainment into the jet determines the composition and temperature distribution in regions where chemical reaction begins. Therefore, the hot-jet ignition method critically requires a fundamental understanding of the jet interaction with the surrounding stream. Due to the complexity of transient turbulent jets, the jet evolution is often analyzed by employing the quasi-steady assumptions which can weakly reflect the jet behavior during an early stage of development. Through an exact solution of momentum equation, the present study models diffusive transport in a round transient jet at high Reynolds numbers. The solution is asymptotically applicable to the shear layer of the jet while a potential core still exists. The expected results address the developing velocity profiles across the jet radius as well as the instantaneous and accumulating entrained mass flux. Upon obtaining the time dependent variations of the velocity, the rate of mass entrainment from the ambient is studied to examine the behavior of characteristic jet velocity on mixing.