24 European Conference on Liquid Atomization and Spray Systems
Turbulent Liquid Atomization
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Turbulent Liquid Atomization In most energy conversion systems, fuel is injected in liquid form. Atomization of the liquid fuel, or the process by which a coherent liquid flow disintegrates into droplets, represents one of the key challenges that remain to be tackled to make predictive simulations possible. Because atomization governs the size of the fuel droplets, and therefore their subsequent evaporation rate, it will have far- reaching repercussions on many aspects of the combustion process, for example pollutant formation. However, the inherent multi-physics and multi-scale nature of this process limits both experimental and numerical investigations. More Info Advanced Numerical Methods for Complex Reacting Turbulent Flows Large eddy simulation (LES) has been shown to be highly suited for the computation of the stronglyunsteady phenomena that occur in combustion devices. Still, LES of multi-physics problems is a young research field, and especially in the areas of multiphase flows and combustion, the required models are often non-existent or lack the desired accuracy. Contrarily to direct numerical simulation (DNS) where all flow scales are resolved, LES separates turbulent flow fields into large-scale resolved and small-scale unresolved components by a spatial filtering procedure, and models the unresolved components. Even resolving only the large-scale turbulence significantly improves the accuracy of flow predictions compared to Reynolds averaged approaches (RANS), while greatly reducing the computational cost in comparison to DNS. More Info Advanced Numerical Methods for Multiphase Flows Because primary atomization represents a challenge for experimentalists, numerical modeling should provide a much needed alternative. However, numerical studies of primary atomization have also been very sparse. To simulate two-phase flows, various techniques have been developed, that all enjoy some benefit and suffer from limitations. Because no clear gold standard has emerged on how to conduct a numerical simulation of complex two-phase flows, the number of direct numerical studies of primary atomization remains limited. Several key issues remain, such as the discontinuous nature of the flow properties across the phase-interface, the singularity of the surface tension forces, and the very large range of scales involved in atomization. More Info Lagrangian and Eulerian Spary Modeling Sprays and other dispersed-phase systems can be described by a kinetic equation containing terms for spatial transport, acceleration, and particle processes (such as evaporation or collisions). In principle, the kinetic description is valid from the dilute (non- collisional) to the dense limit. However, its numerical solution in multi-dimensional systems is intractable due to the large number of independent variables. As an alternative, Lagrangian methods "discretize" the density function into "parcels" that are simulated using Monte-Carlo methods. More Info Gas-solid Risers Gas-particle flows in vertical risers are used in many industries including gasification/pyrolysis for biofuel conversion, coal combustion, and fluid catalytic cracking. Experimental studies have shown riser flows to be unsteady with large solid-volume fraction fluctuations. Regions of densely-packed particles, referred to as clusters and streamers form, which greatly affect the overall flow behavior and mixing properties. A Eulerian-Lagrangian approach is used to simulate riser flows and better understand the cluster formation. The gas phase is solved on an Eulerian grid while each particle is tracked individually. More Info Turbulent Spray Combustion In gas turbine engines, liquid fuel must first evaporate before it can be consumed by combustion. Hence, liquid atomization and vaporization is of paramount importance in combustion systems, and governs how fuel is supplied to the flame. A key element in predicting the complex behavior of gas turbine engines is therefore accurately modeling spray evaporation. Indeed, in reacting multi- phase flows the combustion process is intricately linked to spray evaporation. The energy required by the phase change is provided by the heat of combustion, and the fuel consumed by the flame comes from liquid vaporization creating a complex sub-filtered mixing field. More Info Electrohydrodynamic Atomization Over the past decade, there has been considerable interest in controlling the emissions from small engines in the size range of 200 cm 3 or smaller. Fuel injection schemes may reduce the incidence of pollutant emissions. However, the cost of implementation is a barrier to large scale adoption. The cost of fuel injection is driven by both the need to pump the fuel to the injection pressure and to add parts for the injector head. One approach to small-scale fuel injection is to capitalize upon the benefits of electrohydrodynamics (EHD) and enhance fuel atomization. There are many possible benefits to EHD aided atomization for combustion, such as smaller droplets, wider spray cone, and the ability to control or "tune" the spray for improved performance.
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Transcript of Turbulent Liquid Atomization
Turbulent Liquid Atomization
In most energy conversion systems, fuel is injected in liquid form. Atomization of the liquid fuel, or the process by which a coherent liquid flow disintegrates into droplets, represents one of the key challenges that remain to be tackled to make predictive simulations possible. Because atomization governs the size of the fuel droplets, and therefore their subsequent evaporation rate, it will have far-reaching repercussions on many aspects of the combustion process, for example pollutant formation. However, the inherent multi-physics and multi-scale nature of this process limits both experimental and numerical investigations.
More Info
Advanced Numerical Methods for Complex Reacting Turbulent FlowsLarge eddy simulation (LES) has been shown to be highly suited for the computation of the stronglyunsteady phenomena that occur in combustion devices. Still, LES of multi-physics problems is a young research field, and especially in the areas of multiphase flows and combustion, the required models are often non-existent or lack the desired accuracy. Contrarily to direct numerical simulation (DNS) where all flow scales are resolved, LES separates turbulent flow fields into large-scale resolved and small-scale unresolved components by a spatial filtering procedure, and models the unresolved components. Even resolving only the large-scale turbulence significantly improves the accuracy of flow predictions compared to Reynolds averaged approaches (RANS), while greatly reducing the computational cost in comparison to DNS.
More Info
Advanced Numerical Methods for Multiphase FlowsBecause primary atomization represents a challenge for experimentalists, numerical modeling should provide a much needed alternative. However, numerical studies of primary atomization have also been very sparse. To simulate two-phase flows, various techniques have been developed, that all enjoy some benefit and suffer from limitations. Because no clear gold standard has emerged on how to conduct a numerical simulation of complex two-phase flows, the number of direct numerical studies of primary atomization remains limited. Several key issues remain, such as the discontinuous nature of the flow properties across the phase-interface, the singularity of the surface tension forces, and the very large range of scales involved in atomization.
More Info
Lagrangian and Eulerian Spary ModelingSprays and other dispersed-phase systems can be described by a kinetic equation containing terms for spatial transport, acceleration, and particle processes (such as evaporation or collisions). In principle, the kinetic description is valid from the dilute (non-collisional) to the dense limit. However, its numerical solution in multi-dimensional systems is intractable due to the large number of independent variables. As an alternative, Lagrangian methods "discretize" the density function into "parcels" that are simulated using Monte-Carlo methods.
More Info
Gas-solid RisersGas-particle flows in vertical risers are used in many industries including gasification/pyrolysis for biofuel conversion, coal combustion, and fluid catalytic cracking. Experimental studies have shown riser flows to be unsteady with large solid-volume fraction fluctuations. Regions of densely-packed particles, referred to as clusters and streamers form, which greatly affect the overall flow behavior and mixing properties. A Eulerian-Lagrangian approach is used to simulate riser flows and better understand the cluster formation. The gas phase is solved on an Eulerian grid while each particle is tracked individually.
More Info
Turbulent Spray CombustionIn gas turbine engines, liquid fuel must first evaporate before it can be consumed by combustion. Hence, liquid atomization and vaporization is of paramount importance in combustion systems, and governs how fuel is supplied to the flame. A key element in predicting the complex behavior of gas turbine engines is therefore accurately modeling spray evaporation. Indeed, in reacting multi-phase flows the combustion process is intricately linked to spray evaporation. The energy required by the phase change is provided by the heat of combustion, and the fuel consumed by the flame comes from liquid vaporization creating a complex sub-filtered mixing field.
More Info
Electrohydrodynamic AtomizationOver the past decade, there has been considerable interest in controlling the emissions from small engines in the size range of 200 cm3 or smaller. Fuel injection schemes may reduce the incidence of pollutant emissions. However, the cost of implementation is a barrier to large scale adoption. The cost of fuel injection is driven by both the need to pump the fuel to the injection pressure and to add parts for the injector head. One approach to small-scale fuel injection is to capitalize upon the benefits of electrohydrodynamics (EHD) and enhance fuel atomization. There are many possible benefits to EHD aided atomization for combustion, such as smaller droplets, wider spray cone, and the ability to control or "tune" the spray for improved performance.
