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  • 1
    Electronic Resource
    Electronic Resource
    Direct numerical simulation and subgrid analysis of a transitional droplet laden mixing layer (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 12 (2000), S. 650-671 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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 18×106 grid points are used to discretize the Eulerian gas phase equations and up to 5.7×106 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. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870271
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  • 2
    Electronic Resource
    Electronic Resource
    A priori subgrid analysis of temporal mixing layers with evaporating droplets (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 12 (2000), S. 1573-1591 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Subgrid analysis of a transitional temporal mixing layer with evaporating droplets has been performed using three sets of results from a direct numerical simulation (DNS) database, with Reynolds numbers (based on initial vorticity thickness) as large as 600 and with droplet mass loadings as large as 0.5. In the DNS, the gas phase is computed using an Eulerian formulation, with Lagrangian droplet tracking. The large eddy simulation (LES) equations corresponding to the DNS are first derived, and key assumptions in deriving them are first confirmed by using the DNS database. Since LES of this flow requires the computation of droplet source terms, it is essential to obtain the unfiltered gas-phase variables at droplet locations from filtered gas-phase variables at the grid points. This paper proposes to model these unfiltered gas-phase variables at the drop locations by assuming the gas-phase variables to be the sum of the filtered variables and a correction based on the filtered standard deviation; this correction is then computed from the subgrid scale (SGS) standard deviation. This model predicts the unfiltered variables at droplet locations considerably better than simply interpolating the filtered variables. Three methods are investigated for modeling the SGS standard deviation: the Smagorinsky approach, the gradient model and the scale-similarity formulation. When the proportionality constant inherent in the SGS models is properly calculated, the gradient and scale-similarity methods give results in excellent agreement with the DNS. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870405
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  • 3
    Electronic Resource
    Electronic Resource
    Efficient high-pressure state equations (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1605-1610 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A method is presented for a relatively accurate, noniterative, computationally efficient calculation of high-pressure fluid-mixture equations of state, especially targeted to gas turbines and rocket engines. Pressures above 1 bar and temperatures above 100 K are addressed. The method is based on curve fitting an effective reference state relative to departure functions formed using the Peng-Robinson cubic state equation. Fit parameters for H2, O2, N2, propane, methane, n-heptane, and methanol are given.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430624
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    Paper (German National Licenses)
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