Cebeci-Smith model
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(Copied from B-L model, still pretty rough) |
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- | + | {{Turbulence modeling}} | |
- | + | The Cebeci-Smith [[#References|[Smith and Cebeci (1967)]]] is a two-layer algebraic 0-equation model which gives the eddy viscosity, <math>\mu_t</math>, as a function of the local boundary layer velocity profile. The model is suitable for high-speed flows with thin attached boundary-layers, typically present in aerospace applications. Like the [[Baldwin-Lomax model]], this model is not suitable for cases with large separated regions and significant curvature/rotation effects. Unlike the [[Baldwin-Lomax model]], this model requires the determination of of a boundary layer edge. | |
- | The Cebeci-Smith [[#References|[Cebeci | + | |
== Equations == | == Equations == | ||
- | <table width=" | + | <table width="70%"><tr><td> |
:<math> | :<math> | ||
\mu_t = | \mu_t = | ||
\begin{cases} | \begin{cases} | ||
{\mu_t}_{inner} & \mbox{if } y \le y_{crossover} \\ | {\mu_t}_{inner} & \mbox{if } y \le y_{crossover} \\ | ||
- | {\mu_t}_{outer} & \mbox{if} y > y_{crossover} | + | {\mu_t}_{outer} & \mbox{if } y > y_{crossover} |
\end{cases} | \end{cases} | ||
</math></td><td width="5%">(1)</td></tr></table> | </math></td><td width="5%">(1)</td></tr></table> | ||
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where <math>y_{crossover}</math> is the smallest distance from the surface where <math>{\mu_t}_{inner}</math> is equal to <math>{\mu_t}_{outer}</math>: | where <math>y_{crossover}</math> is the smallest distance from the surface where <math>{\mu_t}_{inner}</math> is equal to <math>{\mu_t}_{outer}</math>: | ||
- | <table width=" | + | <table width="70%"><tr><td> |
:<math> | :<math> | ||
y_{crossover} = MIN(y) \ : \ {\mu_t}_{inner} = {\mu_t}_{outer} | y_{crossover} = MIN(y) \ : \ {\mu_t}_{inner} = {\mu_t}_{outer} | ||
</math></td><td width="5%">(2)</td></tr></table> | </math></td><td width="5%">(2)</td></tr></table> | ||
- | The inner region is given | + | The inner region is given |
- | <table width=" | + | <table width="70%"><tr><td> |
:<math> | :<math> | ||
- | {\mu_t}_{inner} = \rho l^2 \left | + | {\mu_t}_{inner} = \rho l^2 \left[\left( |
+ | \frac{\partial U}{\partial y}\right)^2 + | ||
+ | \left(\frac{\partial V}{\partial x}\right)^2 | ||
+ | \right]^{1/2}, | ||
</math></td><td width="5%">(3)</td></tr></table> | </math></td><td width="5%">(3)</td></tr></table> | ||
where | where | ||
- | <table width=" | + | <table width="70%"><tr><td> |
:<math> | :<math> | ||
l = \kappa y \left( 1 - e^{\frac{-y^+}{A^+}} \right) | l = \kappa y \left( 1 - e^{\frac{-y^+}{A^+}} \right) | ||
</math></td><td width="5%">(4)</td></tr></table> | </math></td><td width="5%">(4)</td></tr></table> | ||
- | + | with the constant <math>\kappa = 0.4</math> and | |
- | + | ||
- | \kappa = 0.4 | + | |
- | </math> | + | |
- | <table width=" | + | <table width="70%"><tr><td> |
:<math> | :<math> | ||
- | \left | + | A^+ = 26\left[1+y\frac{dP/dx}{\rho u_\tau^2}\right]^{-1/2}. |
</math></td><td width="5%">(5)</td></tr></table> | </math></td><td width="5%">(5)</td></tr></table> | ||
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The outer region is given by: | The outer region is given by: | ||
- | <table width=" | + | <table width="70%"><tr><td> |
:<math> | :<math> | ||
{\mu_t}_{outer} = \alpha \rho U_e \delta_v^* F_{KLEB}(y;\delta), | {\mu_t}_{outer} = \alpha \rho U_e \delta_v^* F_{KLEB}(y;\delta), | ||
- | </math></td><td width="5%">( | + | </math></td><td width="5%">(6)</td></tr></table> |
- | where <math>\alpha=0.0168</math> | + | where <math>\alpha=0.0168</math> and <math>\delta_v^*</math> is the velocity thickness given by |
- | <table width=" | + | <table width="70%"><tr><td> |
:<math> | :<math> | ||
- | \delta_v^* = \int_0^\delta (1-U/U_e)dy | + | \delta_v^* = \int_0^\delta (1-U/U_e)dy. |
- | </math></td><td width="5%">( | + | </math></td><td width="5%">(7)</td></tr></table> |
- | + | <math>F_{KLEB}</math> is the Klebanoff intermittency function given by | |
<table width="100%"><tr><td> | <table width="100%"><tr><td> | ||
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F_{KLEB}(y;\delta) = \left[1 + 5.5 \left( \frac{y}{\delta} \right)^6 | F_{KLEB}(y;\delta) = \left[1 + 5.5 \left( \frac{y}{\delta} \right)^6 | ||
\right]^{-1} | \right]^{-1} | ||
- | </math></td><td width="5%">( | + | </math></td><td width="5%">(8)</td></tr></table> |
- | + | ||
== Model variants == | == Model variants == | ||
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== References == | == References == | ||
- | * | + | * {{reference-paper|author=Smith, A.M.O. and Cebeci, T. |year=1967|title=Numerical solution of the turbulent boundary layer equations|rest=Douglas aircraft division report DAC 33735}} |
* {{reference-book|author=Wilcox, D.C. |year=1998|title=Turbulence Modeling for CFD|rest=ISBN 1-928729-10-X, 2nd Ed., DCW Industries, Inc.}} | * {{reference-book|author=Wilcox, D.C. |year=1998|title=Turbulence Modeling for CFD|rest=ISBN 1-928729-10-X, 2nd Ed., DCW Industries, Inc.}} | ||
+ | |||
+ | [[Category:Turbulence models]] | ||
+ | |||
+ | {{stub}} |
Latest revision as of 12:13, 18 December 2008
The Cebeci-Smith [Smith and Cebeci (1967)] is a two-layer algebraic 0-equation model which gives the eddy viscosity, , as a function of the local boundary layer velocity profile. The model is suitable for high-speed flows with thin attached boundary-layers, typically present in aerospace applications. Like the Baldwin-Lomax model, this model is not suitable for cases with large separated regions and significant curvature/rotation effects. Unlike the Baldwin-Lomax model, this model requires the determination of of a boundary layer edge.
Contents |
Equations
| (1) |
where is the smallest distance from the surface where is equal to :
| (2) |
The inner region is given
| (3) |
where
| (4) |
with the constant and
| (5) |
The outer region is given by:
| (6) |
where and is the velocity thickness given by
| (7) |
is the Klebanoff intermittency function given by
| (8) |
Model variants
Performance, applicability and limitations
Implementation issues
References
- Smith, A.M.O. and Cebeci, T. (1967), "Numerical solution of the turbulent boundary layer equations", Douglas aircraft division report DAC 33735.
- Wilcox, D.C. (1998), Turbulence Modeling for CFD, ISBN 1-928729-10-X, 2nd Ed., DCW Industries, Inc..