[Psg.engineering]

Hi everyone,
i want to know the rotating velocity of a vertical axis wind turbine under different wind condition. I put the turbine (radius 50 cm) into a cylinder volume (radius 2 m). I define two domain, the fluid domain and the turbine domain. The fluid domain is Stationary and I define the inlet boundary condition: wind speed 5 m/s. The turbine domain is immersed solid.
How can i determinate the angular velocity of the blade under wind pressure?
I read about the frozen rotor model CFX but i'm a structural engineering and i'm new with CFX and i don't know how can improve it.
Thank you for the answer

[ghorrocks]

Do not use immersed solids to do this. The rotor should be cut out of a rotating domain. Have a look at the example tutorials which come with CFX for how to set up rotating machinery.

Use the following method to get the rotation speed:
1) For a given wind condition, do a simulation (probably frozen rotor) using a rotational speed which is your guess as to what speed it will run at.
2) Then repeat this model with half the rotation speed and double the rotation speed.
3) Then post-process all the models and extract the rotor torque. Include the torque consumed by the load (presumably a generator).
4) For cases when your guessed speed was too slow you should have a net positive torque (indicating the rotor will speed up). For cases when your guessed speed was too fast you should have a net negative toque (indicating the rotor will slow down). The operating speed of the device is where there is no net torque, so the device will run steady state at that speed.
5) Interpolate between your models to get the zero net torque point. Do more simulations if you want to get it more accurately.

This method means you do a number of simple simulations and iterate to the operating speed. It is theoretically possible to use a rigid body model to let it find the operating speed but this is quite a complex model to do and I bet will take far longer than a series of the simple constant speed simulations.

[Psg.engineering]

Thank you very much for your reply.

[Psg.engineering]

How can i define the domain? Is it correct if i define: one cylinder (radius 2m) with domain fluid; one cylinder around the rotor woth domain fluid (radius 0,50 m); one domain solid with the turbine (radius 0,50m). The interface fluid fluid is frozen rotor. In what domain I set the angular velocity?
The analisy type is steady-state?

[ghorrocks]

You define a rotating domain for rotating bits and a stationary domain for the stationary bits. You do not generate a solid domain. Have a look at the CFX tutorials on rotating machinery - they do not use solid domains and neither should you.

You set the rotational speed on the rotating frame of reference domain. If you use frozen rotor the analysis is pseudo-steady state. The rotational flow components are taken care of in the rotating frame of reference and you get a torque/power figure for the blades at that location in their rotation.

Again, the tutorials show how to set all this up. Work through the CFX tutorials.

[Psg.engineering]

Can you send me the tutorial? I have only the cfx-pre tutorial but i can't find this.

[ghorrocks]

The documentation is in the ANSYS documentation, under CFX. The files required to run the tutorials are in the directory <CFX_ROOT>/examples directory. If they are not installed in your installation then reinstall it and ensure they are included.

[Psg.engineering]

Ok, thank you