Forum
Important Notice for New User Registrations
To combat an increasing number of spam and bot registrations, we now manually approve all new user registrations. While this may cause a delay until your account is approved, this step is essential to ensure the quality and security of this forum.
To help us verify your registration as legitimate, please use a clear name as user name or an official email address (such as a work, university, or similar address). If you’re concerned that we may not recognize your registration as non-spam, feel free to email us at with a request to approve your username.
VAWT blade shape: straight vs helical
Hello David,
I am simulating different blade shapes for a VAWT, specifically straight vs helical vs troposkien. I have attached the Cp vs TSR result. The setup used is very similar to the setup mentioned by Balduzzi [2018] in which you were the 2nd author, the only difference is I am using 31 panels for blade discretization instead of 21. Surprisingly, helical and straight almost coincide at all TSR values, whereas from the literature, I was expecting the helical power generation to be pretty different from the straight-bladed VAWT. Also, when I run DMS simulations, both blade shapes give exactly identical power values. This observation is the same if I use different blade discretization (panels) or azimuthal discretization (in deg) or wake length (in rotations).
Do you know what can be the reason for this? Do you think some LLFVW setup changes are necessary? Currently, I am keeping all setup parameters at the default value and swept area is the same for all 3 VAWTs.
Thank you
Shubham
Uploaded files:- You need to login to have access to uploads.
Hi Shubam
I dont know which exact geometries you are simulation, but if the chord length of the blades, the blades and the airfoil(s) used is the same there should be no difference in terms of power generation between a straight blade and a helical blade since the solidity is exactly the same.
Helical blades reduce the torque oscillations though, which you can see when looking at a torque vs azimuth or torque vs time graph.
BR,
David
Hello David,
Thank you for your reply. This is a very interesting comment.
In terms of geometry, I am using 1.5 m blade height, 1.03 m rotor diameter and a 3-bladed rotor with NACA 0021 with 0.086m chord length, for all 3 blade shapes. You used these geometrical parameters for a 1-bladed rotor to validate QBlade with CFD in Balduzzi [2018]. My high-fidelity results are exactly validating power values at TSR 3.3, which you used.
Yes, helical blades are reducing torque oscillations and that’s also helping in noise reduction (from my high-fidelity simulations). But there are 2 main differences from straight bladed rotor: the “rope” length of blades is more and Leading Edge of blade is not orthogonal to the free stream velocity (even though chord is parallel to velocity), in the former. Don’t you think this should create differences in results between the two rotor designs? Or maybe these two differences counter each other (first one increases power due to more surface area of blade and second one decreases power due to part of blade loading contributing to torque along different axes)?
My high fidelity results are showing a decrease in power for helical, along with reducing the torque oscillations in a single rotation.
Thank you
Regards
Shubham
Just to mention that both straight and helical have same swept area, which is 1.5m × 1.03m, in the above discussions.
Hi,
QBlade makes two assumptions when modeling helical blades:
- The aerodynamic panel coordinate system is oriented in the azimuthal direction, so the airfoil cross section is oriented in the azimuthal direction and not normal to the leading edge (see image)
- The panel area is evaluated as half the mangnitude of the cross product of the two panel diagonals: A = abs((LATB * TALB))/2
I guess that this could explain some of the differences to high fidelity sims.
BR,
David
Uploaded files:- You need to login to have access to uploads.
