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SST k-omega model

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The SST k-omega turbulence model [Menter 1994] is a [[Two equation turbulence models|two-equation]] [[Eddy viscosity|eddy-viscosity]] model which has become very popular. The SST formulation combines the best of two worlds. The use of a k-omega formulation in the inner parts of the boundary layer makes the model directly usable all the way down to the wall through the visous sub-layer, hence the SST k-omega model can be used as a [[Low-Re turbulence model]] without any extra damping functions. The SST formulation also switches to a k-epsilon behaviour in the free-stream and thereby avoids the common k-omega problem that the model is too sensitive to the [[Turbulence free-stream boundary conditions|inlet free-stream turbulence properties]]. Authors who use the SST k-omega model often merit it for its good behaviour in adverse pressure gradients and separating flow. The SST k-omega model does produce a bit too large turbulence levels in regions with large normal strain, like stagnation regions and regions with strong acceleration. This tendency is much less pronounced than with a normal k-epsilon model though.
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==Kinematic Eddy Viscosity ==
==Kinematic Eddy Viscosity ==
:<math>
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Revision as of 09:51, 31 May 2007

Turbulence modeling
Turbulence
RANS-based turbulence models
  1. Linear eddy viscosity models
    1. Algebraic models
      1. Cebeci-Smith model
      2. Baldwin-Lomax model
      3. Johnson-King model
      4. A roughness-dependent model
    2. One equation models
      1. Prandtl's one-equation model
      2. Baldwin-Barth model
      3. Spalart-Allmaras model
    3. Two equation models
      1. k-epsilon models
        1. Standard k-epsilon model
        2. Realisable k-epsilon model
        3. RNG k-epsilon model
        4. Near-wall treatment
      2. k-omega models
        1. Wilcox's k-omega model
        2. Wilcox's modified k-omega model
        3. SST k-omega model
        4. Near-wall treatment
      3. Realisability issues
        1. Kato-Launder modification
        2. Durbin's realizability constraint
        3. Yap correction
        4. Realisability and Schwarz' inequality
  2. Nonlinear eddy viscosity models
    1. Explicit nonlinear constitutive relation
      1. Cubic k-epsilon
      2. EARSM
    2. v2-f models
      1. \overline{\upsilon^2}-f model
      2. \zeta-f model
  3. Reynolds stress model (RSM)
Large eddy simulation (LES)
  1. Smagorinsky-Lilly model
  2. Dynamic subgrid-scale model
  3. RNG-LES model
  4. Wall-adapting local eddy-viscosity (WALE) model
  5. Kinetic energy subgrid-scale model
  6. Near-wall treatment for LES models
Detached eddy simulation (DES)
Direct numerical simulation (DNS)
Turbulence near-wall modeling
Turbulence free-stream boundary conditions
  1. Turbulence intensity
  2. Turbulence length scale

The SST k-omega turbulence model [Menter 1994] is a two-equation eddy-viscosity model which has become very popular. The SST formulation combines the best of two worlds. The use of a k-omega formulation in the inner parts of the boundary layer makes the model directly usable all the way down to the wall through the visous sub-layer, hence the SST k-omega model can be used as a Low-Re turbulence model without any extra damping functions. The SST formulation also switches to a k-epsilon behaviour in the free-stream and thereby avoids the common k-omega problem that the model is too sensitive to the inlet free-stream turbulence properties. Authors who use the SST k-omega model often merit it for its good behaviour in adverse pressure gradients and separating flow. The SST k-omega model does produce a bit too large turbulence levels in regions with large normal strain, like stagnation regions and regions with strong acceleration. This tendency is much less pronounced than with a normal k-epsilon model though.

Contents

Kinematic Eddy Viscosity

\nu _T = {a_1 k \over \mbox{max}(a_1 \omega, \Omega F_2) }

Turbulence Kinetic Energy

{{\partial k} \over {\partial t}} + U_j {{\partial k} \over {\partial x_j }} = P_k - \beta ^* k\omega + {\partial \over {\partial x_j }}\left[ {\left( {\nu + \sigma_k \nu _T } \right){{\partial k} \over {\partial x_j }}} \right]

Specific Dissipation Rate

{{\partial \omega } \over {\partial t}} + U_j {{\partial \omega } \over {\partial x_j }} = \alpha S^2 - \beta \omega ^2 + {\partial \over {\partial x_j }}\left[ {\left( {\nu + \sigma_{\omega} \nu _T } \right){{\partial \omega } \over {\partial x_j }}} \right] + 2( 1 - F_1 ) \sigma_{\omega 2} {1 \over \omega} {{\partial k } \over {\partial x_i}} {{\partial \omega } \over {\partial x_i}}

Closure Coefficients and Auxilary Relations

F_2=\mbox{tanh} \left[ \left[ \mbox{max} \left( { 2 \sqrt{k} \over \beta^* \omega y } , { 500 \nu \over y^2 \omega } \right) \right]^2 \right]
P_k=\mbox{min} \left(\tau _{ij} {{\partial U_i } \over {\partial x_j }} , 20\beta^* k \omega \right)
F_1=\mbox{tanh} \left\{ \left\{ \mbox{min} \left[ \mbox{max} \left( {\sqrt{k} \over \beta ^* \omega y}, {500 \nu \over y^2 \omega} \right) , {4 \sigma_{\omega 2} k \over CD_{k\omega} y^2} \right] \right\} ^4 \right\}
CD_{k\omega}=\mbox{max} \left( 2\rho\sigma_{\omega 2} {1 \over \omega} {{\partial k} \over {\partial x_i}} {{\partial \omega} \over {\partial x_i}}, 10 ^{-10} \right )
\phi = \phi_1 F_1 + \phi_2 (1 - F_1)
\alpha_1 = {{5} \over {9}}, \alpha_2 = 0.44
\beta_1 = {{3} \over {40}}, \beta_2 = 0.0828
\beta^* = {9 \over {100}}
\sigma_{k1} = 0.85, \sigma_{k2} = 1
\sigma_{\omega 1} = 0.5, \sigma_{\omega 2} = 0.856

References

  1. Menter, F.R. (1994), "Two-equation eddy-viscosity turbulence models for engineering applications", AIAA Journal, vol. 32, pp. 269-289.
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