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VAWT Results turbulent windfield
Hi David, I don’t quite understand the Cp curves in the simulations with turbulent wind conditions. Unfortunately, there are no error messages, so I can’t quite figure out why the curve shows peaks that aren’t physically possible. I’ve also tried different settings, but unfortunately that doesn’t change anything. Can you help me with this?
Best regards,
Witali
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Hello Witali,
This is actually a question that comes up quite often.
Under turbulent inflow conditions, the power coefficient is not as clearly defined as under steady inflow conditions, since the reference velocity itself is no longer constant. The question is then which velocity should be used to normalize the power.
In QBlade, an instantaneous rotor-averaged inflow velocity is used for this purpose. If the turbulent wind field has a low reference velocity, for example 2 m/s, the local and rotor-averaged inflow velocity can fluctuate very strongly and may even approach zero or become negative at certain time steps. If this very small instantaneous velocity is then used to normalize the power coefficient, the resulting Cp values can become very large, or theoretically even approach infinity if the reference velocity is exactly zero.
In such cases, it is often more meaningful to look directly at power, torque, RPM and thrust. You could possible also evaluate a more suitable Cp using the power output and a fixed reference velocity.
Best regards,
David
