CFD Online Discussion Forums - rotationVelocity in rotatingTotalPressure and SRF

Hello,

I think the computation of the rotationVelocity in rotatingTotalPressure and SRF could be simplified. The piece of code is:

Code:

vector axisHat = omega_/mag(omega_);

vectorField rotationVelocity =

omega_ ^ (patch().Cf() - axisHat*(axisHat & patch().Cf()));

In mathematical formulation this yields to:

$\vec{axis} = \frac{\vec{\omega} }{ |\vec{\omega}|}$
$\vec{V} = \vec{\omega} \times ( \vec{r} - \vec{axis} \bullet (\vec{axis} \bullet \vec{r} ) ) = \vec{\omega} \times \vec{r} - \vec{\omega} \times \vec{axis} \bullet (\vec{axis} \bullet \vec{r} )$

Reformulation of the right term:
$\vec{\omega} \times \vec{axis} \bullet (\vec{axis} \bullet \vec{r} ) = ( \vec{\omega} \times \frac{ \vec{\omega} }{ |\vec{\omega}|} ) \bullet (\vec{axis} \bullet \vec{r} ) = ( \vec{\omega} \times \vec{\omega} ) \bullet \frac{ (\vec{axis} \bullet \vec{r} )}{ |\vec{\omega}|} = \vec{0}$

This reduces the computation of the rotationVelocity to:

$\vec{V} = \vec{\omega} \times \vec{r}$

or in C++

Code:

vectorField rotationVelocity = omega_ ^ patch().Cf();