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Reading in Cl/alpha polars
Dear people,
We are using the Qblade to do some exercises on a VAWT. Up till now everything went fine and we’re grateful.
But now we want to import external Cl/alpha polars that Qblade was not able to produce internally (a stall strip discontinuity modelled near the leading edge). Neither the DMS analysis nor the full free wake simulation give credible results here (negative cp values). We also input polars that were made by Qblade itself: The result was comparably incredible.
Is there an issue with importing cl/alpha polars? And is there a way to solve this?
Thanks and best regards, Guido Zwart.
Hello Guido,
there should not be any issues when importing polar data, as the imported data is treated exactly as if it had been generated directly within QBlade.
The predicted turbine performance is inherently dependent on the polar data used during blade design. A negative Cp value can be a credible simulation outcome, depending on factors such as the blade design (chord, radius, solidity, etc.), the simulated operating point (TSR), and the polar data (particularly lift and drag versus AoA).
Without examining some of this data, it is difficult to determine why a negative Cp is being predicted.
Again, it is important to mention that ultimately VAWT performance should be estimated via lifting line free vortex wake time domain simulations as the double multiple streamtube model for VAWT’s behaves highly inconsistent.
BR,
David
