nutUBlendedWallFunction
boundary condition provides a wall constraint on the turbulent viscosity, i.e. nut
, based on velocity, i.e. U
using a binomial-function wall-function blending method between the viscous and inertial sublayer predictions of nut
for low- and high-Reynolds number turbulence models.nutUBlendedWallFunction
condition inherits some of the traits of the nutWallFunction boundary condition.Required fields:
nut | Turbulent viscosity [m2/s]
The model expressions ([52]):
\[ \nu_t = \max(0, \frac{u_{\tau^*}^2}{|\grad{\u}| + \zeta} -\nu_w) \]
with
\[ u_{\tau^*} = \left( u_{\tau_{vis}}^n + u_{\tau_{log}}^n \right)^{1/n} \]
\[ u_{\tau_{vis}} = \frac{u_p}{y^+} \]
\[ u_{\tau_{log}} = \kappa \frac{u_p}{\ln(E y^+)} \]
where
\( \nu_t \) | = | Turbulent viscosity [m2/s] |
\( u_{\tau^*} \) | = | Friction velocity estimation obtained by iterative means [m/s] |
\( u_{\tau_{vis}} \) | = | \(u_\tau\) computed by the viscous sublayer assumptions [m2/s] |
\( u_{\tau_{log}} \) | = | \(u_\tau\) computed by the inertial sublayer assumptions [m2/s] |
\( \nu_w \) | = | Kinematic viscosity of fluid near wall [m2/s] |
\( y^+ \) | = | Estimated wall-normal height of the cell centre in wall units |
\( \kappa \) | = | von Kármán constant [-] |
\( E \) | = | Wall roughness parameter [-] |
\( u_p \) | = | Magnitude of near wall velocity [m/s] |
\( \u \) | = | Velocity [m/s] |
\( n \) | = | Blending exponent [-] |
\( \zeta \) | = | Small value to prevent floating point exceptions |
Example of the boundary condition specification:
<patchName> { // Mandatory entries (unmodifiable) type nutUBlendedWallFunction; // Optional entries (unmodifiable) n 4.0; // Optional (inherited) entries ... }
where the entries mean:
Property | Description | Type | Required | Default |
---|---|---|---|---|
type | Type name: nutUBlendedWallFunction | word | yes | - |
n | Blending factor | scalar | no | 4.0 |
The inherited entries are elaborated in:
blending
option binomial
or with the deprecated blended
flag set to on
.correctNut()
(called through turbulence->validate
) returns a slightly different value every time it is called. See nutUSpaldingWallFunction.Tutorial
Source code