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Atomization and Sprays
IF: 1.737 5-Year IF: 1.518 SJR: 0.814 SNIP: 1.18 CiteScore™: 2.2

ISSN Print: 1044-5110
ISSN Online: 1936-2684

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Atomization and Sprays

DOI: 10.1615/AtomizSpr.2015006910
pages 285-316

STUDY ON SPRAY INDUCED TURBULENCE USING LARGE EDDY SIMULATIONS

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

ABSTRACT

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.

KEY WORDS: LES, spray, turbulence

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