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Evaluation of stochastic particle dispersion modeling in turbulent round jets

International Journal of Multiphase Flow

Sun, Guangyuan; Hewson, John C.; Lignell, David O.

ODT (one-dimensional turbulence) simulations of particle-carrier gas interactions are performed in the jet flow configuration. Particles with different diameters are injected onto the centerline of a turbulent air jet. The particles are passive and do not impact the fluid phase. Their radial dispersion and axial velocities are obtained as functions of axial position. The time and length scales of the jet are varied through control of the jet exit velocity and nozzle diameter. Dispersion data at long times of flight for the nozzle diameter (7 mm), particle diameters (60 and 90 µm), and Reynolds numbers (10, 000–30, 000) are analyzed to obtain the Lagrangian particle dispersivity. Flow statistics of the ODT particle model are compared to experimental measurements. It is shown that the particle tracking method is capable of yielding Lagrangian prediction of the dispersive transport of particles in a round jet. In this paper, three particle-eddy interaction models (Type-I, -C, and -IC) are presented to examine the details of particle dispersion and particle-eddy interaction in jet flow.

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TYPE Journal Article YEAR 2017
ScopusOSTIDOI

Model sensitivities in LES predictions of buoyant methane fire plumes

2017 Fall Technical Meeting of the Western States Section of the Combustion Institute, WSSCI 2017

Koo, Heeseok K.; Hewson, John C.; Domino, Stefan P.; Knaus, Robert C.

A 1-m diameter methane fire plume has been studied using a large eddy simulation (LES) methodology. Eddy dissipation concept (EDC) and steady flamelet combustion models were used to describe interactions between buoyancy-induced turbulence and gas-phase combustion. Detailed comparisons with experimental data showed that the simulation is sensitive to the combustion model and mesh resolution. In particular, any excessive mixing results in a wider and more diffusive plume. As mesh resolution increases, the current simulations demonstrate a tendency toward excessive mixing.

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TYPE Conference Poster YEAR 2017
ScopusOSTI

Modeling thermal runaway in Lithium-Ion packs as a function of scale and heat source

10th U.S. National Combustion Meeting

Shurtz, Randy S.; Hewson, John C.

As deployment of large-scale Li-Ion battery modules is contemplated, there is a need to understand the propensity for thermal runaway in individual cells and the large-scale thermal failure at the pack level. Sources of thermal energy can lead to runaway including short circuits (internal or external), exothermic processes from overcharge of imbalanced cells, the external environment, and other factors. With battery modules consisting of hundreds or even thousands of cells, it will be necessary to design tolerance to local heat release, regardless of the source. This work presents a chemistry-independent framework for analyzing and modeling thermal runaway that will be demonstrated by applying it to thermal runaway (ignition) and cascading failure (propagation).

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TYPE Conference Poster YEAR 2017
ScopusOSTI

Stochastic modeling of unsteady extinction in turbulent non-premixed combustion

Proceedings of the Combustion Institute

Lackmann, T.; Hewson, John C.; Knaus, Robert C.; Kerstein, A.R.; Oevermann, M.

Turbulent fluctuations of the scalar dissipation rate have a major impact on extinction in non-premixed combustion. Recently, an unsteady extinction criterion has been developed (Hewson, 2013) that predicts extinction dependent on the duration and the magnitude of dissipation rate fluctuations exceeding a critical quenching value; this quantity is referred to as the dissipation impulse. The magnitude of the dissipation impulse corresponding to unsteady extinction is related to the difficulty with which a flamelet is exintguished, based on the steady-state S-curve. In this paper we evaluate this new extinction criterion for more realistic dissipation rates by evolving a stochastic Ornstein-Uhlenbeck process for the dissipation rate. A comparison between unsteady flamelet evolution using this dissipation rate and the extinction criterion exhibit good agreement. The rate of predicted extinction is examined over a range of Damköhler and Reynolds numbers and over a range of the extinction difficulty. The results suggest that the rate of extinction is proportional to the average dissipation rate and the area under the dissipation rate probability density function exceeding the steady-state quenching value. It is also inversely related to the actual probability that this steady-state quenching dissipation rate is observed and the difficulty of extinction associated with the distance between the upper and middle branches of the S-curve.

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TYPE Journal Article YEAR 2017
ScopusOSTIDOI
Results 76–100 of 209
Results 76–100 of 209