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Direct numerical simulation and subgrid analysis of a transitional droplet laden mixing layer

Miller, Richard S. and Bellan, Josette (2000) Direct numerical simulation and subgrid analysis of a transitional droplet laden mixing layer. Physics of Fluids, 12 (3). pp. 650-671. ISSN 1070-6631. doi:10.1063/1.870271.

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Direct numerical simulations of a temporally developing, droplet laden mixing layer undergoing transition to mixing turbulence are conducted. The formulation includes complete two-way couplings of mass, momentum, and energy. As many as 18×10^6 grid points are used to discretize the Eulerian gas phase equations and up to 5.7×10^6 initially polydisperse evaporating droplets are tracked in the Lagrangian reference frame. The complete transition to mixing turbulence is captured for several of the higher Reynolds number simulations and it is observed that increasing the droplet mass loading ratio results in a more “natural” turbulence characterized by increased rotational energy and less influence of the initial forcing perturbations. An increased mass loading also results in increased droplet organization within the layer. An a priori subgrid analysis is then conducted which shows that neglecting subgrid velocity fluctuations in the context of large eddy simulations may result in significant errors in predicting the droplet drag force for Stokes numbers St∼1 (with the flow time scale based on the mean velocity difference and initial vorticity thickness). Similar possible errors of lesser magnitude are also observed for the droplet heat flux and evaporation rate when thermodynamic subgrid fluctuations are neglected. An extension of the eddy interaction model commonly used in Reynolds-averaged simulations is then proposed in order to account for the missing subgrid information. Probability density functions (PDFs) of the subgrid fluctuations calculated across homogeneous planes are shown to be highly intermittent, particularly near the laminar–turbulent boundaries of the mixing layer. However, the actual subgrid PDFs calculated locally are much less intermittent and may be adequately modeled by the Gaussian distribution throughout the majority of the mixing layer. A scale similarity model is then employed to predict both the velocity and thermodynamic subgrid variances. The similarity model is well correlated with the actual subgrid variances and shows good agreement in predicting the local fluctuation intensities when a filter width-dependent model constant is used. The subgrid fluctuation variances acting on the droplets are then shown to be well modeled if the Eulerian subgrid variance model is interpolated to the droplet locations.

Item Type:Article
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URLURL TypeDescription
Bellan, Josette0000-0001-9218-7017
Additional Information:© 2000 American Institute of Physics. Received 13 February 1999; accepted 1 December 1999. This research was conducted at the California Institute of Technology’s Jet Propulsion Laboratory (JPL) and sponsored by General Electric (GE) through the Air Force Office of Scientific Research (AFOSR) Focused Research Initiative program with Dr. Hukam Mongia from GE serving as contract monitor. Computational resources were provided by the supercomputing facility at JPL.
Funding AgencyGrant Number
General ElectricUNSPECIFIED
Air Force Office of Scientific Research (AFOSR)UNSPECIFIED
Issue or Number:3
Record Number:CaltechAUTHORS:20171019-142113982
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Official Citation:Direct numerical simulation and subgrid analysis of a transitional droplet laden mixing layer. Richard S. Miller and Josette Bellan. Physics of Fluids 2000 12:3, 650-671
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:82515
Deposited By: Tony Diaz
Deposited On:19 Oct 2017 21:29
Last Modified:15 Nov 2021 19:51

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