scholarly journals Pressure scrambling effects and the quantification of turbulent scalar flux model uncertainties

2020 ◽  
Vol 5 (8) ◽  
Author(s):  
Zengrong Hao ◽  
Catherine Gorlé
Keyword(s):  
Scalar Flux ◽  
Model Uncertainties ◽  
Flux Model

scholarly journals An explicit algebraic model for the subgrid-scale passive scalar flux

2013 ◽  
Vol 721 ◽  
pp. 541-577 ◽  
Author(s):  
Amin Rasam ◽  
Geert Brethouwer ◽  
Arne V. Johansson
Keyword(s):  
Channel Flow ◽  
Rotation Rate ◽  
Model Performance ◽  
Turbulent Channel Flow ◽  
Passive Scalar ◽  
Subgrid Scale ◽  
Scalar Flux ◽  
Algebraic Form ◽  
New Model ◽  
Flux Model

AbstractIn Marstorpet al. (J. Fluid Mech., vol. 639, 2009, pp. 403–432), an explicit algebraic subgrid stress model (EASSM) for large-eddy simulation (LES) was proposed, which was shown to considerably improve LES predictions of rotating and non-rotating turbulent channel flow. In this paper, we extend that work and present a new explicit algebraic subgrid scalar flux model (EASSFM) for LES, based on the modelled transport equation of the subgrid-scale (SGS) scalar flux. The new model is derived using the same kind of methodology that leads to the explicit algebraic scalar flux model of Wikströmet al. (Phys. Fluids, vol. 12, 2000, pp. 688–702). The algebraic form is based on a weak equilibrium assumption and leads to a model that depends on the resolved strain-rate and rotation-rate tensors, the resolved scalar-gradient vector and, importantly, the SGS stress tensor. An accurate prediction of the SGS scalar flux is consequently strongly dependent on an accurate description of the SGS stresses. The new EASSFM is therefore primarily used in connection with the EASSM, since this model can accurately predict SGS stresses. The resulting SGS scalar flux is not necessarily aligned with the resolved scalar gradient, and the inherent dependence on the resolved rotation-rate tensor makes the model suitable for LES of rotating flow applications. The new EASSFM (together with the EASSM) is validated for the case of passive scalar transport in a fully developed turbulent channel flow with and without system rotation. LES results with the new model show good agreement with direct numerical simulation data for both cases. The new model predictions are also compared to those of the dynamic eddy diffusivity model (DEDM) and improvements are observed in the prediction of the resolved and SGS scalar quantities. In the non-rotating case, the model performance is studied at all relevant resolutions, showing that its predictions of the Nusselt number are much less dependent on the grid resolution and are more accurate. In channel flow with wall-normal rotation, where all the SGS stresses and fluxes are non-zero, the new model shows significant improvements over the DEDM predictions of the resolved and SGS quantities.

Application of a Subfilter-Scale Flux Model over the Ocean Using OHATS Field Data

2009 ◽  
Vol 66 (10) ◽  
pp. 3217-3225 ◽  
Author(s):  
Mark Kelly ◽  
John C. Wyngaard ◽  
Peter P. Sullivan
Keyword(s):  
Field Data ◽  
Pressure Fluctuations ◽  
Model Resolution ◽  
Scalar Flux ◽  
Terra Incognita ◽  
Air Interface ◽  
Momentum Fluxes ◽  
Flux Model ◽  
Horizontal Array ◽  
Effect Of Surface

Abstract Simple rate equation models for subfilter-scale scalar and momentum fluxes have previously been developed for application in the so-called “terra incognita” of atmospheric simulations, where the model resolution is comparable to the scale of turbulence. The models performed well over land, but only the scalar flux model appeared to perform adequately over the ocean. Analysis of data from the Ocean Horizontal Array Turbulence Study (OHATS) reveals a need to account for the moving ocean–air interface in the subfilter stress model. The authors develop simple parameterizations for the effect of surface-induced pressure fluctuations on the subfilter stress, leading to good predictions of subfilter momentum flux both over land and in OHATS.

Assessment of two-equation models of turbulent passive-scalar diffusion in channel flow

1992 ◽  
Vol 238 ◽  
pp. 405-433 ◽  
Author(s):  
Kiyosi Horiuti
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Eddy Diffusivity ◽  
Passive Scalar ◽  
Scalar Flux ◽  
Scalar Fluxes ◽  
Large Eddy ◽  
Scalar Variance ◽  
Flux Model ◽  
Kim Model

Models for the transport of passive scalar in turbulent flow were investigated using databases derived from numerical solutions of the Navier—Stokes equations for fully developed plane channel flow, these databases being generated using large-eddy and direct numerical simulation techniques. Their reliability has been established by comparison with the experimental measurements of Hishida. Nagano & Tagawa (1986). The present paper compares these simulations and calculations using the Nagano & Kim (1988) ‘two-equation’ model for the scalar variance (kθ) and scalar variance dissipation (εθ). This model accounts for the dependence of flow quantities on the Prandtl number by expressing eddy diffusivity in terms of the ratio of the timescales of velocity and scalar fluctuations. However, the statistical analysis by Yoshizawa (1988) showed that there was an inconsistency in the definition of the isotropic eddy diffusivity in the Nagano—Kim model, the implications of which are clearly demonstrated by the results of this paper where large-eddy simulation and direct numerical simulation (LES/DNS) databases are used to compute the quantities contained in both models. An extension of the Nagano-Kim model is proposed which resolves these inconsistencies, and a further development of this model is given in which the anisotropic scalar fluxes are calculated. Near a rigid surface, a third-order ‘anisotropic representation’ of scalar fluxes may be used as an alternative model for reducing the eddy diffusivity, instead of the conventional ‘damping functions’. This model is similar but distinct from the algebraic scalar flux model of Rogers, Mansour & Reynolds (1989). A third aspect of this paper is the use of the LES/DNS databases to evaluate certain coefficients (those for modelling the pressure-scalar gradient terms) of another model of a similar type, namely the algebraic scalar flux model of Launder (1975).

Investigation of a Two-Equation Turbulent Heat Transfer Model Applied to Ducts

2003 ◽  
Vol 125 (1) ◽  
pp. 194-200 ◽  
Author(s):  
Masoud Rokni and ◽  
Bengt Sunde´n
Keyword(s):  
Heat Transfer ◽  
Eddy Diffusivity ◽  
Turbulent Heat Transfer ◽  
Transfer Model ◽  
Turbulent Heat ◽  
Scalar Flux ◽  
Eddy Viscosity Model ◽  
Wide Range ◽  
Flux Model ◽  
Prandtl Numbers

This investigation concerns numerical calculation of fully developed turbulent forced convective heat transfer and fluid flow in ducts over a wide range of Reynolds numbers. The low Reynolds number version of a non-linear eddy viscosity model is combined with a two-equation heat flux model with the eddy diffusivity concept. The model can theoretically be used for a range of Prandtl numbers or a range of different fluids. The computed results compare satisfactory with the available experiment. Based on existing DNS data and calculations in this work the ratio between the time-scales (temperature to velocity) is found to be approximately 0.7. In light of this assumption an algebraic scalar flux model with variable diffusivity is presented.

Data-driven scalar-flux model development with application to jet in cross flow

2020 ◽  
Vol 147 ◽  
pp. 118931 ◽  
Author(s):  
Jack Weatheritt ◽  
Yaomin Zhao ◽  
Richard D. Sandberg ◽  
Satoshi Mizukami ◽  
Koichi Tanimoto
Keyword(s):  
Model Development ◽  
Cross Flow ◽  
Data Driven ◽  
Scalar Flux ◽  
Jet In Cross Flow ◽  
Flux Model

scholarly journals Improved Subfilter-Scale Models from the HATS Field Data

2007 ◽  
Vol 64 (5) ◽  
pp. 1694-1705 ◽  
Author(s):  
Stephen C. Hatlee ◽  
John C. Wyngaard
Keyword(s):  
Numerical Modeling ◽  
Field Data ◽  
Stress Model ◽  
Scalar Flux ◽  
Terra Incognita ◽  
Advection Term ◽  
Scale Models ◽  
Flux Model ◽  
Horizontal Array ◽  
Grid Mesh

Abstract An earlier paper proposed simple rate-equation models for subfilter-scale (SFS) scalar flux and deviatoric stress in the terra incognita—that is, in numerical modeling applications where the filter (grid-mesh) scale is of the order of the scale of the turbulence. Here the physics in these models is extended and further tested against data from the Horizontal Array Turbulence Study (HATS) experiment. It is found that extensions of the SFS scalar-flux model do not appreciably improve its performance, although an advection term (which could easily be used in modeling applications) substantially and realistically increases the fluctuation level of SFS scalar flux. The addition of buoyancy and rapid-mean-shear terms to the SFS stress model does improve its performance, bringing it to the level of the scalar-flux model.

Explicit algebraic scalar flux approximation

AIAA Journal ◽  
1997 ◽  
Vol 35 ◽  
pp. 985-989
Author(s):  
Y. Shabany ◽  
P. A. Durbin
Keyword(s):  
Scalar Flux ◽  
Flux Approximation
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