Second Moment Closure Modeling and Direct Numerical Simulation of Stratified Shear Layers

Buoyant shear layers are encountered in many engineering and environmental applications, and have been studied by researchers in the context of experiments and modeling for decades. Often, these flows have high Reynolds and Richardson numbers, and this leads to significant/intractable space-time resolution requirements for DNS or LES modeling. On the other hand, many of the important physical mechanisms in these systems, such as stress anisotropy, wake stabilization, and regime transition, inherently render eddy viscosity-based RANS modeling inappropriate. Accordingly, we pursue second-moment closure (SMC), i.e., full Reynolds stress/flux/variance modeling, for moderate Reynolds number non-stratified, and stratified shear layers for which DNS data is available. A range of sub-model complexity is pursued for the diffusion of stresses, density fluxes and variance, pressure strain and scrambling, and dissipation. These sub-models are evaluated in terms of how well they are represented by DNS in comparison to the exact Reynolds averaged terms, and how well they impact the accuracy of the full RANS closure. For the non-stratified case, the SMC model predicts the shear layer growth rate and Reynolds shear stress profiles accurately. Stress anisotropy and budgets are captured only qualitatively. Comparing DNS of exact and modeled terms, inconsistencies in model performance and assumptions are observed, including inaccurate prediction of individual statistics, nonnegligible pressure diffusion, and dissipation anisotropy. For the stratified case, shear layer and gradient Richardson number growth rates, and stress, flux and variance decay rates, are captured with less accuracy than corresponding flow parameters in the non-stratified case. These studies lead to several recommendations for model improvement.

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Work Title Second Moment Closure Modeling and Direct Numerical Simulation of Stratified Shear Layers
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Open Access
Creators
  1. Naman Jain
  2. Hieu T. Pham
  3. Xinyi Huang
  4. Sutanu Sarkar
  5. Xiang Yang
  6. Robert Kunz
License In Copyright (Rights Reserved)
Work Type Article
Publisher
  1. Journal of Fluids Engineering
Publication Date February 16, 2022
Publisher Identifier (DOI)
  1. https://doi.org/10.1115/1.4053444
Deposited June 05, 2023

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Version 1
published

  • Created
  • Added Final_Appeared.pdf
  • Added Creator Naman Jain
  • Added Creator Hieu T. Pham
  • Added Creator Xinyi Huang
  • Added Creator Xinyi Huang
  • Added Creator Xiang Yang
  • Added Creator Sutanu Sarkar
  • Added Creator Hieu Pham
  • Added Creator Xiang Yang
  • Added Creator Sutanu Sarkar
  • Added Creator Robert Kunz
  • Published
  • Updated Publisher, Description, Publication Date Show Changes
    Publisher
    • Journal of Fluids Engineering, Transactions of the ASME
    • Journal of Fluids Engineering
    Description
    • Buoyant shear layers are encountered in many engineering<br>and environmental applications, and have been studied by<br>researchers in the context of experiments and modeling for<br>decades. Often, these flows have high Reynolds and Richardson<br>numbers, and this leads to significant/intractable space-time<br>resolution requirements for DNS or LES modeling. On the other<br>hand, many of the important physical mechanisms in these systems,<br>such as stress anisotropy, wake stabilization, and regime<br>transition, inherently render eddy viscosity-based RANS modeling<br>inappropriate. Accordingly, we pursue second-moment closure<br>(SMC), i.e., full Reynolds stress/flux/variance modeling, for<br>moderate Reynolds number non-stratified, and stratified shear<br>layers for which DNS data is available. A range of sub-model<br>complexity is pursued for the diffusion of stresses, density fluxes<br>and variance, pressure strain and scrambling, and dissipation.<br>These sub-models are evaluated in terms of how well they are<br>represented by DNS in comparison to the exact Reynolds averaged<br>terms, and how well they impact the accuracy of the full<br>RANS closure.<br>For the non-stratified case, the SMC model predicts the<br>shear layer growth rate and Reynolds shear stress profiles accurately.<br>Stress anisotropy and budgets are captured only qual-<br>itatively. Comparing DNS of exact and modeled terms, inconsistencies<br>in model performance and assumptions are observed,<br>including inaccurate prediction of individual statistics, nonnegligible<br>pressure diffusion, and dissipation anisotropy. For<br>the stratified case, shear layer and gradient Richardson number<br>growth rates, and stress, flux and variance decay rates, are captured<br>with less accuracy than corresponding flow parameters in<br>the non-stratified case. These studies lead to several recommendations<br>for model improvement.
    • Buoyant shear layers are encountered in many engineering and environmental applications, and have been studied by researchers in the context of experiments and modeling for decades. Often, these flows have high Reynolds and Richardson numbers, and this leads to significant/intractable space-time resolution requirements for DNS or LES modeling. On the other hand, many of the important physical mechanisms in these systems, such as stress anisotropy, wake stabilization, and regime transition, inherently render eddy viscosity-based RANS modeling inappropriate. Accordingly, we pursue second-moment closure (SMC), i.e., full Reynolds stress/flux/variance modeling, for moderate Reynolds number non-stratified, and stratified shear layers for which DNS data is available. A range of sub-model complexity is pursued for the diffusion of stresses, density fluxes and variance, pressure strain and scrambling, and dissipation. These sub-models are evaluated in terms of how well they are represented by DNS in comparison to the exact Reynolds averaged terms, and how well they impact the accuracy of the full RANS closure. For the non-stratified case, the SMC model predicts the shear layer growth rate and Reynolds shear stress profiles accurately. Stress anisotropy and budgets are captured only qualitatively. Comparing DNS of exact and modeled terms, inconsistencies in model performance and assumptions are observed, including inaccurate prediction of individual statistics, nonnegligible pressure diffusion, and dissipation anisotropy. For the stratified case, shear layer and gradient Richardson number growth rates, and stress, flux and variance decay rates, are captured with less accuracy than corresponding flow parameters in the non-stratified case. These studies lead to several recommendations for model improvement.
    Publication Date
    • 2022-04-01
    • 2022-02-16
  • Deleted Creator Xinyi Huang
  • Deleted Creator Hieu Pham
  • Deleted Creator Xiang Yang
  • Deleted Creator Sutanu Sarkar
  • Updated Creator Sutanu Sarkar
  • Updated Creator Robert Kunz
  • Updated