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VAWT - average torque = 0, and TSR very low for 1dof system

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Old   November 8, 2019, 12:57
Default VAWT - average torque = 0, and TSR very low for 1dof system
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Joachim Hansen
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I am simulating a H-rotor VAWT (Vertical Axis Wind Turbine) with three blades using ANSYS Fluent, and I have set up the rotor to allow free rotation around its centre axis (1dof system). My inlet wind speed is 15 m/s, Iíve made ANSYS calculate the moment for each timestep and I use NACA0018 as the aerofoil-design type. After approximately 5 seconds (transient study with the blades standing still to begin with), the rotor has reached a steady state, and from the motion history written, I can see the angular velocity corresponds to a tip speed ratio of 0.06. Furthermore, the average of my moment values is very close to zero, which makes sense in that the rotor is not accelerating Ė it rotates with a constant speed. However, power is calculated as the product of the average torque and angular velocity, but since the average torque is zero, then I donít produce any power, which shouldnít be the case?

I have also tried to set the rotor to rotate with a constant angular velocity that corresponds to a TSR = 4. This gives me torque-values that are negative for a positive angular velocity, hence the power is negative. This means the rotor needs to receive energy to maintain its rotational velocity, which again is contradictory to how a wind turbine works.

One thing, I am not sure about is how you can include the resistance by the generator, since this depends on the magnetic flux etc.? One of my professors said that because I do not include frictional resistance in the simulation, then the simulation can either go to infinity, since there is nothing slowing it down, or it can reach a steady state, which is what has happened to mine. I just donít understand why I got the second option? And why I get the solutions and numbers that I get?

Appreciate your time and any input can be a massive help.
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