Multiple Injector Model for Primary Breakup of a Liquid Jet in Crossflow

Abstract

R ADIAL injection of liquid jets into a high-velocity and hightemperature cross stream at elevated pressures has various applications in fuel injection systems and advanced aircraft engines, such as gas turbines, afterburners, augmenters, and various combustors. Since this type of fuel injection can improve the fuel atomization and vaporization characteristics, it is commonly used in turbojet augmenter sections and rich burn-quick quench-lean burn, lean premixed prevaporized, and ramjet and scramjet combustion systems. To date, several analytical, experimental, and numerical studies have investigated various characteristics of the jet-incrossflow (JICF) atomization. Experimental studies have developed several correlations that predict various features of the JICF atomization. Because of the nature of the experimental studies, the results and correlations proposed by each study aremainly applicable within the specific parameter ranges of that study. The JICF atomization problem involves very complex physics, such as strong vortical structures, small-scale wave formation, stripping of small droplets from the jet surface, and formation of ligaments and droplets with a wide range of sizes. The JICF atomization process can be divided into three main phases: 1) injection of a liquid jet perpendicular to a gaseous crossflow, 2) deflection and deformation of the jet, and 3) disintegration of the jet into ligaments and droplets. The atomization mechanism is believed to start by the growth of waves that form on the surface of the jet after injection from the nozzle. The relative velocity between the gas and the liquid phase amplifies the surface waves up to the point where the jet breaks up into smaller droplets. Apart from the three phases mentioned above, more complex small-scale physical processes are involved in the problem, such as particle stripping from the jet. From the computational point of view, the complete numerical simulation of such a problem, resolving most important flow scales on the Eulerian frame, is still expensive, especially for industrial applications. These issues signal the demand for some simpler yet reliable models that can be used for industrial design purposes and, at the same time, take into account the flow conditions and the physical properties of the liquid and gas phases. In this paper, we review some of the challenges involved in modeling of the JICF atomization and propose a model that provides realistic predictions of the jet atomization in crossflows. Our focus will be turbulent jets. To validate the model, we perform several experiments. We first validate our experiments by showing that their resulting correlations are in good agreement with the available literature. Then, we use our experimental results to validate our model results. We decided to perform our own experiments rather than making comparisons to previous studies for twomain reasons. First, we needed spatial droplet size and velocity distributions downstream of the nozzle. Although there are studies available that provide that information (such asWu et al. [1]), they mostly consider laminar jets, whereas we are focused on turbulent jets. Second, performing our own experiments provides us with all the information we need to set up our simulations from initial flow parameters to geometrical specifications. A review of some of the experimental studies devoted to studying various characteristics of the JICF problem can be found in Mashayek andAshgriz [2].Wewill present a brief review on some of the experimental and theoretical literature more relevant to the purposes of this paper. One of the first models for atomization of a liquid phase injected normal to a gas stream was that of Reitz [3]. He modeled the atomization by estimating the wavelength and growth rate of the surface waves and relating the breakup droplet sizes to the wavelengths. Liu et al. [4] also modeled a liquid jet injected normal to a gas stream by successive injection of droplets into the gas phase. They did not consider the stripping of droplets from the surface of the jet and Received 24 April 2010; revision received 6 April 2011; accepted for publication 8 April 2011. Copyright © 2011 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Copies of this paper may be made for personal or internal use, on condition that the copier pay the $10.00 per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923; include the code 0001-1452/11 and $10.00 in correspondence with the CCC. ∗Department of Physics, 60 St. George Street. Department of Civil Engineering, 35 St. George Street. ; Department of Mechanical and Industrial Engineering, King’s College Road (Corresponding Author). AIAA JOURNAL Vol. 49, No. 11, November 2011