Shear Layer Dynamics in a Reacting Jet in Crossflow

This study explores the effect of heat release on the growth of the shear layer vortical structures in a reacting jet in crossflow. Jets composed of mixtures of hydrogen, helium and nitrogen were used to independently vary the momentum flux ratio (J), jet to crossflow density ratio (S) and heat release. Velocity fields were obtained from 10 kHz high-speed stereoscopic particle image velocimetry (SPIV) and regions of elevated temperature/combustion products from simultaneous OH planar laser induced fluorescence (OH-PLIF). The shear layer vortices (SLV) originating from instabilities in the windward and leeward shear layers were identified using vortex identification indicator functions in order to track their spatial location and strength. The results show that the asymmetries in shear layer strength between the windward and leeward shear layers are dependent primarily on J, for both reacting and non-reacting flow-fields. The SLV growth rate dependencies on J and S is found to match trends noted by previous studies for non-reacting jets, where SLV growth rates increase with degree of global instability of the JICF. Heat release is also shown to suppress the SLV growth rates relative to non-reacting cases with the same jet parameters. Related to this point, the degree of lifting of the flame also has a significant impact on SLV growth. As flame lifting is directly related to autoignition times, this point shows strong coupling between kinetic rates and jet hydrodynamic stability. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.