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OpenFoam - DynamicMesh SphericalAngularDamper value

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Old   August 16, 2021, 12:09
Default OpenFoam - DynamicMesh SphericalAngularDamper value
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Hi all,

At the moment I am modelling the efficiency for a hydraulic turbine in OpenFOAM. The generated theoretical power results from the product of angular velocity and torque around the turbine axis.

For this purpose I use the dynamic mesh solver sixDoFRigidBodyMotion. From a sensitivity analysis it follows that the sphericalAngularDamper restraint has a large influence on the modelled angular velocity and torque (see attachment).

This parameter has the unit [Nms/rad] and represents friction against angular motion. It acts in the opposite direction with respect to the angular motion.

The parameter is defined as follows:

Code:
restraints
{
    //- Some dumping functions
    translationDamper
    {
            //- Nms/rad
            //  Acts against motion as friction
            sixDoFRigidBodyMotionRestraint  sphericalAngularDamper;
            coeff 500;
    }
}
My question is: how do I estimate the value of the coefficient for the turbine? If I know from the manufacturer that the overall efficiŽncy of this turbine is about 90%, can I transfer this efficiency into a coefficient for anuglar friction?

I hope to hear from you!

Best,
Bas
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File Type: png CFD-Turbine_Angvel_Torque.png (143.3 KB, 10 views)
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Old   October 4, 2021, 07:04
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I discovered that there are multiple ways to find optimum operational conditions for a turbine in order to yield maximum production. The first is by running multiple simulations with a forced rotation for various rotational speeds (under a constant flow velocity). The second one is to apply a model with free rotation (and a fixed flow velocity) whilst varying the angular friction coefficient until one finds optimum conditions. Hence, the angular friction coefficient is not a term one knows on beforehand, but one must search for an optimum value that leads to maximum production of the turbine.
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