Jet in cross-flow (JICF) or transverse jet, is a broadly employed configuration in different environmental and industrial applications. In combustion applications specifically, cross-flow fuel injections are used in gas-turbine combustors and high-speed propulsion systems 1. It is also used to enhance fuel-air mixing in aerospace gas turbine for secondary fuel or dilution air injection 2, 3) and in stationary gas turbines for low NOx staged combustors 4. In high speed combustion systems, flames should be stabilized close to the jet exit while in low NOx gas turbines the flame stabilization occurs further downstream, thus the rate of fuel-oxidizer mixing are very important parameters in in fuel injection systems design 5 6. The mixing and combustion in JICF are highly influenced by three-dimensional coherent vortical structures namely the horseshoe vortex, the wake vortex, the leading-edge and lee-side shear layer vortices and The counter-rotating vortex pair (CVP). The latter is the main vortical structures of JICF and persists in the jet far-field resulting in a better entrainment and mixing compared with a coflow jet 7-9.

The wide practical application, rich physics and its capability to use as a benchmark flow for mixing and combustion models validation, the turbulent non-reacting and reacting JICF has attracted the attention of great many studies. Comprehensive reviews of JICF studies are given in Refs. 2, 10-12. Non-reacting JICF’s are investigated both experimentally 13-20 and numerically 21-30. In these studies effect of some influencing parameters (such as jet to cross-flow density, velocity and momentum ratios, jet Reynolds number, jet arrays, jet nozzle, and jet swirl and pulsation) on the JICF vortical structures and flow and mixing characteristics have been investigated.In comparison with non- reacting JICF, the theoretical and experimental studies considering reacting JICF are limited. Through experimental observations in reacting JICF 6, 31-43, Sullivan et al. 40 have investigated the reacting jets in a high-temperature vitiated cross-flow for a wide range of momentum ratios (0.

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41 studied the flow field characteristics and flame stabilization behavior of a premixed ethylene-air jet into a vitiated hot crossflow. They developed new jet trajectory correlations for reacting and non-reacting JICFs considering the effects of cross-flow confinement. Sullivan et al. 40 and Wagner et al. 41 also reported that the flame stabilization behavior and location can be influenced by different factors such as aerodynamic strain rate, jet to cross-flow momentum ratio, jet angle, jet geometry, fuel and cross-flow conditions (chemical composition and temperature). Steinberg et al. 6 employed the particle image velocimetry and OH planar laser induced fluorescence (advanced laser diagnostics) to investigate the stabilization of reacting hydrogen JICF for various momentum ratios. They concluded that for flush-mounted JICF, the flame along the jet centerline plane consisted of two branches, one lee-stabilized” branch and other “lifted” branch.

Recently, direct numerical simulation (DNS) was also used to investigate the flame structure, flame stabilization and auto-ignition in the reacting JICF 5, 38, 44-47. Grout el .al 45 investigated the flame stabilization mechanism of H2/N2 square JICF using DNS for a velocity ratio of 4.5 and Reynolds number of 4000. They showed that the flame is stabilized in the jet wake with stoichiometric mixture fraction. The effect of injection angle on the flame stabilization mechanism in a round H2/N2 JICF using DNS has also been studied by Kolla et al. 5.

Later, Minamoto et al 38 investigated the effect of fuel composition (increasing the concentration CO relative to H2) on the near field flame stabilization of reacting sysgas JICF using DNS. Lyra et al. 46 studied (non)reacting hydrogen rich jet into the vitiated cross-flow using high speed laser diagnostics and DNS and observed a burner-attached flame. Duo to high computational cost of DNS, use of reliable combustion models for application in large-eddy simulations (LES) is inevitable.

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