[Mohammad80]

Originally Posted by ghorrocks

1. If you have a model of the mechanical link from the wheel to the generator with all the losses and efficiencies then yes.

2. It looks like a horribly coarse mesh to me, causing it to jiggle around everywhere. The results are bound to be very inaccurate. See my post #38.

According to the first point, if we can get the torque which is generated on the rigid body and get the angular velocity of the spinning wheel, then the predicted power will be equals to: P= Torque * w, where "w" is the angular velocity in rad/sec. as I know there is a function in the CFD-post used to calculate the torque around the rotational axis, but what about the angular speed? I am trying to explain what is in my mind but I don't know if it is right or not.

With the second point, I just want to say that I used only the mass moment of inertia about the rotational axis, which is Izz and I neglected the mass moments of inertia of the other directions, which are Ixx, Iyy, Ixy, Iyz and Ixz. Shall I use the three mass moments of inertia, Ixx, Iyy and Izz? I guess the problem is being with the mass moments because I refined the mesh and the solution is going well.

[Mohammad80]

I hope anyone can help me with my questions...

[ghorrocks]

If the wheel you model does not have an external torque applied (ie just inertia) then the torque is zero and there is no power. You need an external torque to generate power.

If the wheel only rotates about one axis then the other moments of inertia are not important.

[Mohammad80]

Originally Posted by ghorrocks

If the wheel you model does not have an external torque applied (ie just inertia) then the torque is zero and there is no power. You need an external torque to generate power.

If the wheel only rotates about one axis then the other moments of inertia are not important.

I have an idea but I don't know if it is logical or not. If I use just the inertia to get motion and after that counting by eye how many revolutions the wheel can make per minute, (so I will get the angular velocity), and then repeat the simulation depending on the rotational speed I got and leave the mass moments and only give the wheel that rotational speed and then I think I will get the torque and the power. Could you please give me your opinion about this idea?

[ghorrocks]

I do not understand your question. Do you mean you will run the simulation with a defined rotation speed? In that case moments of inertia do not matter. But in this configuration the device will produce (or absorb) an external torque and therefore produce (or absorb) power.

[Mohammad80]

Originally Posted by ghorrocks

I do not understand your question. Do you mean you will run the simulation with a defined rotation speed? In that case moments of inertia do not matter. But in this configuration the device will produce (or absorb) an external torque and therefore produce (or absorb) power.

Exactly, this is what Iam thinking of. I am thinking to do first a simulation depending on the inertia force to get the angular speed (by counting the revolutions that the wheel can do per minute) and after that I will do another simulation with a defind angular speed depending on the angular velocity value that I got from the first run and I will neglect the inertia effect in the second run. Do you think that this idea is logical and can be applied to get the power? Best regards.

[ghorrocks]

You need to look at the system.

The rotor is the power source. It will produce a power versus rotational speed curve. Note that the power at the free wheeling speed will be zero as no net torque is generated.

Then the device being powered as a power versus rotational speed curve. Where those two curves intersect is where the device will run at steady state (rotor torque equals device torque).

So think of your rotor as one half of a system, and you need to establish the performance curve. You then match it to the performance curve of the device and you cna understand the system operating point.

[Mohammad80]

Originally Posted by ghorrocks

You need to look at the system.

The rotor is the power source. It will produce a power versus rotational speed curve. Note that the power at the free wheeling speed will be zero as no net torque is generated.

Then the device being powered as a power versus rotational speed curve. Where those two curves intersect is where the device will run at steady state (rotor torque equals device torque).

So think of your rotor as one half of a system, and you need to establish the performance curve. You then match it to the performance curve of the device and you cna understand the system operating point.

Thanks a lot for your notes. I will try to find the performance curve and see how it goes.