[aghsin]

Hi Glenn
I read in one of your previous post that running a serious Steady State simulation to find a rotational speed of rotor is the easiest approach. I wanna know if I run a series of steady state simulation with different rotor rpm, how I can get conclusion about the real rpm of rotor from the graph rpm vs torque?

[ghorrocks]

It is a simple thing then to integrate through time the rpm versus torque curve to model the rotor speed versus time. The maths to do this is straight forward and should be easily done in Excel, matlab, python or whatever you like to do basic numerical work in.

[aghsin]

Glenn,
thank you for your reply. you said somewhere that extrapolating to find a net zero torque in torque vs rpm curve will give us the actual rotating speed. would you please let me know the concept behind this?

[ghorrocks]

Basic mechanics - if the rotor has zero torque then it runs at constant speed. So find the point where the fluid power equals the absorbed power and you have your steady state operating point.

[aghsin]

Glenn,
Thank you for your help. I performed a simulation of axial turbine from start up based on Rigid body approach and I got almost the same result compared your suggestion (series of steady state simulation). I got almost the same rotational speed of rotor in both approach. In both case the torque got zero when the rotor get a steady rotation, I was wounder how I can calculate a power output based on the equation P=TW, now? Because torque=0.

[ghorrocks]

If the rotor is just freewheeling around then there is no output power. But if the power/torque is being absorbed in the generator (or whatever is absorbing the power) then you just get the power straight from that.

[siw]

Glenn,

How would you apply the steady-state approach if the rotating blades are obscured over some regions of the rotation, e.g. the attached image of a simple example (I've removed a lot of the geometry for clarity)? Here steady-state simulations would be needed at different angles.

I too want to simulate the blades spinning up from rest due to the freestream velocity.

Thanks

[ghorrocks]

Nothing is attached. But no matter, I think I understand your question.

If you want to use the frozen rotor approach but have a configuration where there will be torque variations depending on rotor angle, then you need to do enough frozen rotor simulations at enough angles so you know the torque versus angle curve well enough that you can determine an average power.

[siw]

Glenn,

Updated the post with the image.

[Héctor Lodoso]

Originally Posted by ghorrocks

Far easier, but a little less elegant is to sweep through a range of rotation speeds in a series of steady state runs. This will give you a torque/power versus speed curve. Then interpolate on this curve your intended torque/power and there you have it. If you like then run this point as well to improve the accuracy of the interpolation.

Hello Mr. Horrocks,

What do you exactly mean with the quoted sentence?
I do not understand the concept "steady state runs" when you talk at the same time of "rotation speed" of the rotor. Is the rotor actually moving (rotating) in a transient simulation? Or do you mean to compute the rotation speed throug the inlet wind velocity? ....

[ghorrocks]

By steady state runs I mean use frozen rotor or one of those simplified rotating frames of reference models which accounts for the frame rotation inside a steady state simulation.

[Héctor Lodoso]

Originally Posted by ghorrocks

By steady state runs I mean use frozen rotor or one of those simplified rotating frames of reference models which accounts for the frame rotation inside a steady state simulation.

Thank you for your reply.

Then I understand it is a sweep of pure steady state simulations or with the use moving reference frames. But then, how could I take into account the rotation speed of the rotor in a pure steady state run?

Please excuse my ignorance.

[ghorrocks]

If the simulation is purely steady state with no rotating frames of reference then you can't account for the rotation. It is the rotating frame of reference model which accounts for the rotation.