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Danville, CA, United States

Sannan S.,Sintef | Kerstein A.R.,72 Lomitas Road
Energy Procedia | Year: 2016

Differential molecular diffusion effects are expected to be of particular importance in the combustion of hydrogen and H2-enriched fuels. The mixing between fuel and oxidizer can be significantly influenced, implying changed chemical reaction rates and overall heat release. Here, the LEM3D model based on the Linear Eddy Model (LEM) is employed to simulate differential diffusion effects in a turbulent round jet of H2 and Freon 22 issuing into air. Input to LEM3D, generated from ANSYS Fluent, consists of velocity profiles and profiles for the turbulent diffusivity, the Kolmogorov scale and the integral length scale. In this paper, the LEM3D-Fluent coupling is demonstrated by a coarse steady-state RANS simulation in Fluent with a one-to-one correspondence between the RANS grid cells and the LEM3D control volumes. The LEM3D simulation results are compared with previously obtained measurements of differential molecular diffusion for the given flow configuration.

Kerstein A.R.,72 Lomitas Road
Journal of Fluid Mechanics | Year: 2014

A novel concept for simulation of turbulent mixing, termed hierarchical parcel swapping (HiPS), was recently proposed. The method involves either a parameterized representation of the turbulent flow or a more self-contained flow simulation. As a step toward turbulent mixing applications, the latter formulation is used for the first numerical demonstration of model performance. Owing to its suitability for this purpose and its role as a canonical benchmark, channel flow is the target application. Despite its idealized representation of this flow, HiPS is shown to capture salient features of the flow with a notable degree of quantitative accuracy. The implications of this finding with regard to flow physics and with regard to the applicability of HiPS to other problems are discussed. © 2014 Cambridge University Press.

Sannan S.,Sintef | Kerstein A.R.,72 Lomitas Road
Energy Procedia | Year: 2013

The LEM3D stochastic model for numerical simulation of turbulent mixing is used to simulate differential molecular diffusion effects in an isothermal jet of hydrogen and Freon 22 issued into air. The computations are compared with a published experimental study of the flow configuration. Salient features of the measured results are reproduced qualitatively, but the absence of spatial variation of the smallest eddy motion in LEM3D omits the streamwise variation of this length scale in the experimental configuration, resulting in a systematic deviation from the experimental trend. A first-principles basis for incorporating this missing physics into LEM3D is described, indicating the path forward for physically based quantitative prediction of differential diffusion effects, and turbulent combustion phenomenology more generally, using LEM3D. © 2013 Published Elsevier Ltd.

Kerstein A.R.,72 Lomitas Road
Journal of Statistical Physics | Year: 2013

An economical representation of effects of turbulence on the time-evolving structure of diffusive scalar fields is obtained by introducing a hierarchical (tree) network connecting fluid parcels, with effects of turbulent advection represented by swapping pairs of sub-trees at rates determined by turbulence time scales associated with the sub-trees. The fluid parcels reside at the base of the tree. The tree structure partitions the fluid parcels into adjacent pairs (or more generally, p-tuples). Adjacent parcels intermix at rates governed by diffusion time scales based on molecular diffusivities and parcel sizes. This simple procedure efficiently accomplishes long-standing objectives of turbulent mixing model development, such as generating physically based time histories of fluid-parcel nearest-neighbor encounters and the associated spatial structure of turbulent scalar fields. Correspondences between features of the hierarchical formulation and turbulent mixing phenomenology, both generic and case-specific, are noted. © 2013 The Author(s).

Schulz F.T.,TU Brandenburg | Glawe C.,TU Brandenburg | Schmidt H.,TU Brandenburg | Kerstein A.R.,72 Lomitas Road
Environmental Earth Sciences | Year: 2013

Although pipe transport for storage of CO2 captured from combustion exhaust is most efficient under supercritical conditions, subcritical multi-phase transport might sometimes occur intentionally or unintentionally. To adequately assess the consequences of subcriticality, the fidelity of subcritical multi-phase turbulent transport modeling, including confinement and buoyancy effects, must be improved. For this reason, an extension of one-dimensional turbulence, a stochastic turbulence modeling strategy, for application to this regime is underway. As a step toward this extension, a turbulent liquid jet issuing from a planar channel is simulated and results are compared with liquid jet measurements and channel flow numerical simulations. A previously noted turbulence decay scaling is reproduced, suggesting that the scaling is more robust than might be supposed, given the complicating factors. This work provides a basis for extension to the primary breakup regime of liquid jets and hence to subcritical multi-phase turbulence more generally. © 2013 Springer-Verlag Berlin Heidelberg.

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