The Cebeci–Smith model is a 0-equation eddy viscosity model used in computational fluid dynamics analysis of turbulent boundary layer flows. The model gives 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 a boundary layer edge.
The model was developed by Tuncer Cebeci and Apollo M. O. Smith, in 1967.
Equations
In a two-layer model, the boundary layer is considered to comprise two layers: inner (close to the surface) and outer. The eddy viscosity is calculated separately for each layer and combined using:

where
is the smallest distance from the surface where
is equal to
.
The inner-region eddy viscosity is given by:
![{\displaystyle {\mu _{t}}_{\text{inner}}=\rho \ell ^{2}\left[\left({\frac {\partial U}{\partial y}}\right)^{2}+\left({\frac {\partial V}{\partial x}}\right)^{2}\right]^{1/2}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/975d15728657f393bb633583ad74f2e7b2291bc7)
where

with the von Karman constant
usually being taken as 0.4, and with
![{\displaystyle A^{+}=26\left[1+y{\frac {dP/dx}{\rho u_{\tau }^{2}}}\right]^{-1/2}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/a6cbfbe9463cf56057c39d277960e194c1127502)
The eddy viscosity in the outer region is given by:

where
,
is the displacement thickness, given by

and FK is the Klebanoff intermittency function given by
![{\displaystyle F_{K}=\left[1+5.5\left({\frac {y}{\delta }}\right)^{6}\right]^{-1}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/c22f259c44011383d4f65bf71c49674772212cf7)