Begell House
Atomization and Sprays
Atomization and Sprays
1044-5110
25
4
2015
SPRAY IN AUTOMOTIVE APPLICATIONS: PART I
Qingluan
Xue
Argonne National Laboratory
v-vii
STUDY ON SPRAY INDUCED TURBULENCE USING LARGE EDDY SIMULATIONS
Spray induced turbulence is investigated on a number of different computational fluid dynamics (CFD) grids of varying mesh sizes using a non-viscosity dynamic structure large eddy simulation (LES) turbulence model. Turbulent flow is induced inside a quiescent chamber by liquid fuel spray. Coherent structures (CS) generated from this turbulent flow are constructed and visualized using λ2 definition. Using CS, analysis is performed on the turbulent flow around the liquid spray jet. The visualization of CS helps to explain the mechanism of fuel-air mixing obtained from LES results. It is found that fine mesh (with average mesh size of 0.5 mm) LES results predicts fuel-air mixing by virtue of the breaking down of large eddies to a number of smaller eddies. These LES are then compared against the results from RANS calculations on the same flow situations. It was found that main the difference between RANS and LES flow structures was in LES's prediction of the breakdown of large flow structures into a number of smaller eddies and the nature of diffusion of fuel rich pockets. A local CFD mesh criterion is derived based on the observation of these CS for LES calculations. With finer mesh (0.25 mm average mesh sizes or smaller), more flow structures were predicted resulting in enriched statistic of flow prediction. It is found that the LES dynamic structure model is effective in resolving turbulent flow structures around spray jets. CFD grid convergence is obtained in mesh size of ~ 0.5 mm or smaller. Furthermore this study shows that gas phase turbulence is induced due to spray liquid−gas momentum exchange in the secondary breakup region. Turbulent structures generated in the maximum spray drag regions are then carried to a downstream location due to large-scale surrounding motions. Away from the spray in downstream locations, turbulent structures break down to smaller scales and produce intermittencies in flow and fuel-air mixing mechanism.
Siddhartha
Banerjee
Engine Research Center, University of Wisconsin−Madison, Madison, Wisconsin, 53706, USA
Christopher J.
Rutland
Engine Research Center, University of Wisconsin−Madison, Madison, Wisconsin, 53706, USA
285-316
A GIBBS ENERGY RELAXATION (GERM) MODEL FOR CAVITATION SIMULATION
In this paper, a comprehensive highly compressible and turbulent two-fluid multispecies model is presented. It involves an equation for the transport of the liquid volume fraction in addition to two different sets of partial differential equations for the gas and the liquid phase. The multicomponent gas phase is governed by an ideal gas equation of state (EOS) while the stiffened gas EOS is specified to the single-component liquid phase. In this work, a Reynolds averaged Navier-Stokes (RANS) formulation is adopted. For the turbulence, a standard k − ε model is used for the gas phase while a turbulent viscosity-based model is used for the liquid phase in order to improve the laminar-turbulent transition computation through the nozzle. In addition, the model equations include different relaxation terms for mass, momentum, and energy exchanges at the liquid-gas interfaces. For the present cavitation modeling, an instantaneous relaxation procedure is used for the velocity, pressure, and temperature; while a slower procedure is adopted for the Gibbs free-energy relaxation model (GERM) at the interfaces. These models have been applied for the simulation of the cavitation inside a transparent single-hole nozzle. The obtained cavitation pocket has a similar shape as the experiments. Moreover, two different cavitation regimes have been identified. A gaseous cavitation regime appears in a region in which the static pressure is close to but above the liquid saturation pressure; a second cavitation regime may happen when the static pressure goes below the liquid saturation pressure. In the latter case, the liquid become superheated and leads to a vaporous cavitation regime. Also, the cooling of the fuel and the density variation due to the expansion of compressible liquid through the nozzle is among the more interesting findings of this paper.
Chawki
Habchi
IFP Energies Nouvelles, let 4 Avenue de Bois-Preau, 92852 Rueil-Malmaison, France
317-334
A SPHERICAL VOLUME INTERACTION DDM APPROACH FOR DIESEL SPRAY MODELING
This work presents an implementation and evaluation of an alternative approach for describing exchange of mass, momentum, and energy in diesel spray computational fluid dynamics (CFD) simulations using discrete droplet modeling (DDM). During the calculation, each parcel in the domain is surrounded by a spherical volume of ambient gas and interacts first with it instead of interacting directly with the cell volume hosting the parcel. In this way, the interaction volume is independent of the mesh and can be located in more than one cell. This model was implemented using the Open-FOAM CFD opensource C++ library. It was developed with the aim to reduce grid dependencies related to spray-grid mutual orientation and to the choice of the injector nozzle position with respect to the cell hosting it. All the submodel constants were set to match experimental data of a chosen baseline case in nonreactant vaporizing conditions. Then the new approach predictions were first compared to standard DDM on moving the injector position within the hosting cell and later on varying ambient density and injection pressure of fuel. Also, a study of the dependency of the results on the spray-grid mutual orientation was carried out. High-speed imaging and Rayleigh-scattering measurements taken from the engine combustion department (ECN) web database were used to assess numerical results: a good accuracy in the predictions of liquid and vapor spray penetration as well as axial and radial mixture fraction profiles, can be simultaneously achieved on varying thermophysical and geometrical settings. If applied to engine calculations, then the reduced dependency on the nozzle position becomes appreciable when injector with multiple nozzles are used.
Roberto
Torelli
Dipartimento di Energia, Politecnico di Milano, via Lambruschini 4, 20158 Milan, Italy
Gianluca
D'Errico
Dipartimento di Energia, Politecnico di Milano, via Lambruschini 4, 20158 Milan, Italy
Tommaso
Lucchini
Dipartimento di Energia, Politecnico di Milano, via Lambruschini 4, 20158 Milan, Italy
V.
Ikonomou
Caterpillar UK Engines Company Ltd., Frank Perkins Way, Eastfield, Peterborough PE1 5NA, United Kingdom
R. M.
McDavid
Caterpillar Inc, Technical Center−Bldg F, P.O. Box 1875, Peoria IL 61656-1875
335-374