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Nonlinear SGS Model

A-priori and a-posteriori tests of models were performed using DNS results. Anisotropy and material frame indifference (MFI) requirements for models in rotating systems were used to help construct new models based on the dynamic structure approach. The results were then analyzed in terms of several representative characteristics, including correlation and regression coefficients of individual components, resolved kinetic energy, SGS energy production, molecular dissipation, and kinetic energy spectrum. For all measures examined, the MFI-consistent dynamic structure models perform significantly better able to capture essential features of rotating turbulence, especially for rotating turbulence.

As a simple alternative to the standard eddy-diffusivity closure, a nonlinear SGS approach (including a SGS stress model and a SGS flux model) is introduced and implemented in simulations of the ABL flows. The new approach computes the structure of the SGS stress/flux (relative magnitude) based on the normalized gradient term, which is derived from the Taylor expansion. The SGS magnitudes are estimated based on the local-equilibrium hypothesis. The model formulation is assessed through a systematic comparison with well-established theoretical predictions and reference results of various flow statistics. Simulation results obtained with the use of this new approach show good agreement with the reference results and an evident improvement over results obtained using traditional eddy-viscosity/diffusivity models.

 

References

  • A-priori tests of one-equation LES modeling of rotating turbulence, Hao Lu, Christopher J. Rutland, and Leslie M. Smith, Journal of Turbulence, 8(37): 1-27, 2007
  • A-posteriori tests of one-equation LES modeling of rotating turbulence, Hao Lu, Christopher J. Rutland, and Leslie M. Smith, International Journal of Modern Physics C, 19(12): 1949-1964, 2008
  • A modulated gradient model for large-eddy simulation: Application to a neutral atmospheric boundary layer, Hao Lu and Fernando Porté-Agel, Physics of Fluids, 22, 2010
  • Assessment of the modulated gradient model in decaying isotropic turbulence, Hao Lu, Theoretical & Applied Mechanics Letters, 1: 041005, 2011
  • A modulated gradient model for scalar transport in large-eddy simulation of the atmospheric boundary layer, Hao Lu and Fernando Porté-Agel, Physics of Fluids, 25, 2013
  • On the development of a dynamic non-linear closure for large-eddy simulation of the atmospheric boundary layer, Hao Lu and Fernando Porté-Agel, Boundary-Layer Meteorology, 2014
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