[BasG]

Hi CFD-friends,

At the moment I am modelling the power generation of a hydraulic turbine in OpenFOAM. The resulting power is the product of angular velocity X torque around the turbine axis.

For this purpose I use a dynamic solver (sixDoFRigidBodyMotion). By means of sensitivity analysis I figured out that the results (both angular frequency and torque) are very sensitive to the value we specify for the spericalAngularDamper (see attachment). This parameter has a unit of Nms/rad. It can be seen as a friction force that acts in opposite direction with respect to the rotating motion of the turbine blades. It is defined as follows in the dynamicMeshDict:

restraints
{
    rotationDamper
    {
            //- Nms/rad
            //  Acts against motion as friction
            sixDoFRigidBodyMotionRestraint  sphericalAngularDamper;
            coeff 100; //default 10
    }
}

My question is: how can we estimate this coefficient while we do not yet have field measurements or practical esimtations? In other words, how do I find a proper estimation of this value for preliminary assessment of the power generation of the turbine?

Hope to hear from you.

Best,
Bas