Learning Forum

[Nate K.]

Hello Forum,

I have looked far and wide for help in plotting the tangential velocity at the outer edge of my Darrieus H-type vertical axis wind turbine but to no avail. (Or help with acquiring angular velocity since tangential velocity is a function of angular velocity). I have seen someone create the plot using "area-weighted average" tangential velocity and then creating an expression with this divided by rotor radius. And I have done this, however, the values seem too low and seems dividing by radius is not correct as it would imply the weighted-average velocity is at the center of rotation (its likley actually at the center of mass of rotation when it is the area-weighted average, right?... a bit of a separate question although knowing this, perhaps, I could then change my turbine r to this new distance for a correct equation...). 

Any input on how to acquire the tangetial or angular velocity would be much appreciated.

Thanks, Nate 

[Federico]

 

Hello Nate, 

unfortunately, there is currently no direct way to plot angular velocity other than using some crude methods, as the one that you have found in previous posts. 

If you are using the 6DOF model as your previous post suggests, you can check the Write Motion History box when defining 6DOF properties. This will write to file the time, XYZ coordinates [m] and theta_XYZ angle [deg] for the center of gravity of your rigid body. You can then use a 3rd party tool to calculate and plot angular velocity.

 

[Nate K.]

 

 

Hi Federico,

I see. Thanks for sharing. I will plot some other parameters then. Although, do you know more about this area-weighted average tangential velocity? Is it tangential velocity at the radius which is at the average area of an airfoil? Seems I could calculate for this radius (even if closely estimating it by a visual) then get an approximate tangential velocity at outer edge of the turbine (perhaps this what you mean by having “crude methods”?)… cause to have tangential velocity means having tangential velocity at a certain radius...

 

 

[Federico]

Hello Nate, 

the area-weigthed average tangential velocity will really only work for a circular motion of a cylindrical domain. If you know the radius and tangential velocity of this motion, you can work out the angular velocity. You really only need 1 point that has these two quantities over time. The area-averaging is only to reduce the noise in this calculation.

 You can read about how Tangential velocity is defined here: 41.2. Velocity Reporting Options (ansys.com)

In your case, with airfoils, I still recommend using the data from Motion History.