- #1
HauTo
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Hello everyone, i have a question, how to find wind turbine rotor rotation speed based on freewheel rotation speed of rotor (RPM)(torque = 0)? Thanks for your attention.
Thank you very much for your answer. It is very helpful for me.Baluncore said:Welcome to PF.
The unloaded speed will be when the angle of attack of the blade airfoil is close to zero. As power is extracted from the rotor, the angle of attack will increase to between about 5° and 15°, and the rotor will slow down. If you try to extract more energy from the rotor, the airfoil will begin to stall at higher angles of attack. You need to operate the rotor at an optimum angle of attack.
Note that there is a twist along the turbine blades. That allows for the blade velocity due to rotation increasing with radius, and the angle of attack remaining close to optimum along the blade. The angle of attack relates the ratio of the blade velocity to the wind velocity.
Without more blade airfoil details your question can only be answered approximately. I will have to check my maths, but I believe the relationship between angle of attack, a, loaded RPM, Va, and unloaded RPM, Vo, goes something like;
Va = Vo * ( 1 - Sin( a ) )
As an example, let us assume that the optimum angle of attack is 12°,
For a = 12°, 1 - Sin(12°) = 0.792 = 79.2 % of the unloaded speed.
Just another question, sir. In Well Turbines situation, Is the above method still valid? This is my blade airfoil below. Thanks for your attention.Baluncore said:Welcome to PF.
The unloaded speed will be when the angle of attack of the blade airfoil is close to zero. As power is extracted from the rotor, the angle of attack will increase to between about 5° and 15°, and the rotor will slow down. If you try to extract more energy from the rotor, the airfoil will begin to stall at higher angles of attack. You need to operate the rotor at an optimum angle of attack.
Note that there is a twist along the turbine blades. That allows for the blade velocity due to rotation increasing with radius, and the angle of attack remaining close to optimum along the blade. The angle of attack relates the ratio of the blade velocity to the wind velocity.
Without more blade airfoil details your question can only be answered approximately. I will have to check my maths, but I believe the relationship between angle of attack, a, loaded RPM, Va, and unloaded RPM, Vo, goes something like;
Va = Vo * ( 1 - Sin( a ) )
As an example, let us assume that the optimum angle of attack is 12°,
For a = 12°, 1 - Sin(12°) = 0.792 = 79.2 % of the unloaded speed.
"Well Turbines", maybe it is confused in translation ?HauTo said:In Well Turbines situation, Is the above method still valid? This is my blade airfoil below.
You might use 1-Sin(a) as a crude or approximate design guide for an initial computer model, but you will have to do some real experiments, to verify it gives a sensible prediction. I see no other way to predict the maximum power point, MPP.HauTo said:Can I use other factors to calculate rotational speed with the existing unload rotational speed?