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H-Darrieus Cp Values
Hello Adam,
the turbine you are simulating is likely one of the most challenging VAWT cases to simulate for several reasons:
a) The rated TSR is close to 1, leading to angles of attack fluctuating by approximately ±50° during each revolution. This results in significant dynamic stall, and most engineering dynamic stall models (including those in QBlade) are not well-suited for such large variations in the angle of attack resulting from high solidity rotors.
b) The Reynolds number is very low, ranging between 20,000 and 200,000, and varies significantly. In this range, the polars are typically highly sensitive to the Reynolds number, making it difficult to find or generate accurate polar data.
c) The rotor has a high solidity, and the blades are simple, straight, and untapered. This results in a large circulation gradient at the blade ends, causing strong tip vortices and significantly affecting the induced velocities in the tip region.
These factors collectively make it quite challenging to accurately model the turbine in a code like QBlade. The simulation will be highly sensitive to the choice of dynamic stall models, unsteady attached aerodynamic models, wake vortex settings, and blade discretization in the tip region.
You mentioned that the experimental data was validated with LES simulations, which are typically actuator line simulations that also use airfoil polar data similarly to the LLFVW in QBlade. Obtaining more details about the setup of these LES simulations could help you refine your results further.
BR,
David
Hi David,
Appreciated for your reply, is that mean using the LLFVW method can get a good results like 3D-LES CFD by tunning the dynamic_stall model, wake vortex settings and so on?
By the way, if I succeed to replicating the experimental results by tunning the parameters, could I keep these settings to develop a new VAWT with high solidity, such as 0.5 or 0.6. How can I ensure the reliability of simulation results without the referring data to compare with?
Best Regards,
Adam
Hello Adam,
the most crucial part is to obtain realistic airfoil polar data.
As mentioned, secondary effects such as dynamic stall, virtual camber, Reynolds number variation, unsteady attached flow aerodynamics, and tip effects play a significant role in high solidity VAWTs operating at tip speed ratios (TSRs) close to 1.
Accurately modeling such turbines requires experience, and validation with experimental data is highly recommended. I don’t believe there is an “easy” solution to ensure reliable results; each of the factors mentioned above must be carefully accounted for.
BR,
David
Hi David,
Appreciated for your reply, I also think it’s not an easy work that reproduce the experimental data for such a high solidity vawt. To push the project forward, I’m planning to obtain the airfoil polar data through CFD tools. Before that, I’d like to ask your suggestions about which method is much more suitable for Qblade simulations, 2d-cfd or 3d-cfd. As known to all, 3d-cfd can take the effect ot the finite length into account which is whether considered twice in qblade.
Meanwhile, I’m devoted to the same work of a new vawt with the solidity of 0.45 and the rated TSR of 1.96.
Quote from jdhzct2025 on 5. September 2024, 10:44Hi David,
Appreciated for your reply, I also think it’s not an easy work that reproduce the experimental data for such a high solidity vawt. To push the project forward, I’m planning to obtain the airfoil polar data through CFD tools. Before that, I’d like to ask your suggestions about which method is much more suitable for Qblade simulations, 2d-cfd or 3d-cfd. As known to all, 3d-cfd can take the effect ot the finite length into account which is whether considered twice in qblade.
Meanwhile, I’m devoted to the same work of a new vawt with the solidity of 0.45 and the rated TSR of 1.96. In the range of near the rated TSR, the simulations can have a good agreement with the experimental data. However, when the TSR below 1.6, the vawt couldn’t harvest the wind energy as in the experiment. In addition, I have tried to over-estimate the performance below 1.6 using the single Polars with Re280k, but it fails. Could you help me check the simulation and give me some suggestions?
Best Regards,
Adam
There is a bug in typing the text, sincere apology.
Adam
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Hi Adam,
your results dont look too bad. I got similar Cp results with your design, retuning the wake settings.
BR,
David
P.S. The polar data that you are using seems to have an issue around the point of negative stall. Smoothing the curve in that reagion can potentially improve results…
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