Ct or not Ct ? that is the question (2005-02-29)

[Old Forum Archivist]

An example is Enercon where Power versus Wind Speed is presented based on 'easy' measurements by the manufacturer or other organisation. But, where do Ct figures come from and why are they required ? More accurately, can Ct be computed from P-U (with some assumptions) ? Practically, the easiest way of 'producing' a new turbine file is to use an old one and enter the new Power numbers per wind speed. What happens when the existing Ct values are left unchanged ?



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Ct is - per definition - the dimensionless thrust excerted on the turbine rotor by the wind, as explained in the WAsP HELP system. It is used for calculating the turbine-turbine wake effect in wind farms. It cannot - in general - be calculated from the power curve, as it will e.g. depend on the regulating system (based on blade-pitching or stall). However, it will, contrary to the power curve, be practically independent of the air density. Ct should be supplied by the turbine manufacturer together with the power curve. Normally the manufacturers will supply the Ct-curve upon request.

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