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Zeta-f model

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The ''zeta-f'' model is a robust modification of the elliptic relaxation model. The set of equations, for the incompressible Newtonian fluid, constituting the <math>\zeta-f</math> model is given below.
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The ''zeta-f'' model is a robust modification of the elliptic relaxation model. For the incompressible Newtonian fluid the final set of equations constituting the <math>\zeta-f</math> model is given below.

Revision as of 15:11, 25 January 2007

The zeta-f model is a robust modification of the elliptic relaxation model. For the incompressible Newtonian fluid the final set of equations constituting the \zeta-f model is given below.


Contents

Turbulent viscosity \nu_t

\nu_t = C_\mu \, \zeta \, k \, T

Turbulent kinetic energy k

\frac{\partial k}{\partial t} + U_j \frac{\partial k}{\partial x_j} = P_k - \varepsilon + \frac{\partial}{\partial x_j} \left[ \left( \nu + \frac{\nu_t}{\sigma_{k}} \right) \frac{\partial k}{\partial x_j} \right]

Turbulent kinetic energy dissipation rate \varepsilon

\frac{\partial \varepsilon}{\partial t} + U_j \frac{\partial \varepsilon}{\partial x_j} = \frac{C_{\varepsilon 1} P_k - C_{\varepsilon 2} \varepsilon}{T} + \frac{\partial}{\partial x_j} \left[ \left( \nu + \frac{\nu_t}{\sigma_{\varepsilon}} \right) \frac{\partial \varepsilon}{\partial x_j} \right]

Normalized velocity scale \zeta

\frac{\partial \zeta}{\partial t} + U_j \frac{\partial \zeta}{\partial x_j} = f - \frac{\zeta}{k} P_k + \frac{\partial}{\partial x_j} \left[ \left( \nu + \frac{\nu_t}{\sigma_{\zeta}} \right) \frac{\partial \zeta}{\partial x_j} \right]

Elliptic relaxation function f

L^2 \nabla^2 f - f = \frac{1}{T} \left( C_1 - 1 + C'_2 \frac{P_k}{\varepsilon} \right) \left( \zeta - \frac{2}{3} \right)

Production of the turbulent kinetic energy P_k


P_k = - \overline{u_i u_j} \frac{\partial U_j}{\partial x_i}


 P_k = \nu_t S^2

Modulus of the mean rate-of-strain tensor S

S \equiv \sqrt{2S_{ij} S_{ij}}

Turbulence time scale T

T = max \left[ min \left( \frac{k}{\varepsilon},\, \frac{0.6}{\sqrt{6} C_{\mu} |S|\zeta} \right), C_T  \left( \frac{\nu^3}{\varepsilon} \right)^{1/2} \right]

Turbulence length scale L

L = C_L \, max \left[ min \left( \frac{k^{3/2}}{\varepsilon}, \,
  \frac{k^{1/2}}{\sqrt{6} C_{\mu} |S| \zeta} \right), C_{\eta}
  \left( \frac{\nu^3}{\varepsilon} \right)^{1/4} \right]

Model coefficients

C_\mu = 0.22, \sigma_{k} = 1, \sigma_{\varepsilon} = 1.3, \sigma_{\zeta} = 1.2, C_{\varepsilon 1} = 1.4 (1 + 0.012 / \zeta), C_{\varepsilon 2} = 1.9, C_1 = 1.4, C_2' = 0.65, C_T = 6, C_L = 0.36 and C_{\eta} = 85.

References

  • Popovac, M., Hanjalic, K. Compound Wall Treatment for RANS Computation of Complex Turbulent Flows and Heat Transfer, Flow, Turbulence and Combustion, DOI 10.1007/s10494-006-9067-x, 2007.
  • Hanjalic, K., Popovac, M., Hadziabdic, M. A robust near-wall elliptic-relaxation eddy-viscosity turbulence model for CFD, Int. J. Heat Fluid Flow, 25, 1047–1051, 2004.


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