Computational Prediction of Primary Breakup in Fuel Spray Nozzles for Aero-Engine Combustors

Abstract

Primary breakup of liquid fuel in the vicinity of fuel spray nozzles as utilized in aero-engine combustors is numerically investigated. As grid based methods exhibit a variety of disadvantages when it comes to the prediction of multiphase flows, the "Smoothed Particle Hydrodynamics" (SPH)-method is employed. The eligibility of the method to analyze breakup of fuel has been demonstrated in recent publications by Braun et al, Dauch et al and Koch et al [1,2,3,4]. In the current paper a methodology for the investigation of the two-phase flow in the vicinity of fuel spray nozzles at typical operating conditions is proposed. Due to lower costs in terms of computing time, 2D predictions are desired. However, atomization of fluids is inherently three dimensional. Hence, differences between 2D and 3D predictions are to be expected. In course of this study, predictions in 2D and based on a 3D sector are presented. Differences in terms of gaseous flow, ligament shape and mixing are assessed. Keywords Multiphase Flows -Fuel Atomization -Smoothed Particle Hydrodynamics -Aero-Engine -Combustor IntroductionAiming at a reduction of pollutant emissions of air-traffic, academia and industry both invest in research to investigate processes causing the formation of pollutants of aero-engine combustors. One aspect influencing the formation of pollutants is the quality of the injected fuel spray and its placement within the gaseous flow field of the combustion chamber. Because of limited optical access and challenging thermodynamic conditions, experimental studies are costly and cannot provide detailed information about breakup of the fuel in the close vicinity of fuel injectors. Hence, numerical investigations analyzing the local two-phase flow are desired. At the "Institut für Thermische Strömungsmaschinen" (ITS) a numerical code based on the Lagrangian "Smoothed Particle Hydrodynamics" (SPH)-method has been developed by Koch, Hoefler and Braun [5,4]. The objective is to predict the liquid fuel breakup in the close vicinity of the fuel spray nozzle. Conventional grid based methods exhibit a variety of inherent shortcomings, which can be overcome by a fully Lagrangian approach. In recent publications the potential of the code in terms of two-phase flow predictions has been demonstrated successfully by Braun et al, Dauch et al and Keller et al [1,3,6]. Current state-of-the art methods for combustor design do not take into account the details of primary breakup. Correlations based on empirical studies are employed to impose droplet initial conditions for subsequent EulerLagrangian CFD predictions. These correlations must be tuned to each individual setup and need to be calibrated. Most of the correlations are valid only for low pressures and temperatures. A detailed simulation of primary breakup can overcome these shortcomings. It might provide transient droplet initial conditions, which can be used as input for subsequent Euler-Lagrangian predictions. Even if SPH computations are too costly for every day design studies, the...

Analyzing the Interaction of Vortex and Gas–Liquid Interface Dynamics in Fuel Spray Nozzles by Means of Lagrangian-Coherent Structures (2D)

“…However, the general conclusions drawn from this paper can analogously be transferred to 3D. Please refer to Dauch et al [8] for a comparison between 2D and 3D simulations of primary breakup in airblast atomizers in order to learn more about the limitations of 2D setups.…”

“…Various studies have demonstrated the suitability of this combination of quadratures for the prediction of multiphase flows, as presented by Braun [4], Koch [5], and Dauch [7,8]. Following the weakly compressible approach, the pressure is determined by means of an equation of state (EOS).…”

“…Hence, an adequate smaller computational domain and realistic boundary conditions need to be defined. In this study, the computational domain comprises the inner and outer air ducts as well as the exit of the fuel gallery according to Dauch et al [8]. The fuel spray nozzle geometry is displayed in Figure 3 on the left-hand side, and the resulting computational domain in Figure 3 on the right.…”

“…The slip walls are defined in order to mimic the movement of the flow in a radially outward direction. Please refer to Dauch et al [8] for further details about the extraction of the slip walls and the typical shape of the velocity profiles imposed at the inlet of the domain. In the present case, the geometry of the fuel gallery exit is subject to modifications compared to the geometry investigated by Dauch et al [8].…”

“…A numerical code based on the SPH method has been developed at the Institut für Thermische Strömungsmaschinen (ITS). The suitability of the code to predict the primary breakup of fuel in generic, but also realistic, industrial use cases has been demonstrated by Braun and Koch [4][5][6] and Chaussonnet and Dauch [7][8][9].…”