[CFD-Lover]

Hey CFD community,

I know that this topic might be too specific to discuss it in this forum since I don't know any other forums might deal with wind turbines discussion. I am trying to design an optimum blade using three different airfoils for a specific wind speed and turbine diameter. I was wondering if anyone has been dealing with this topic before could find some time to help get up to speed. I would really appreciate any help.

Thanks for your time in advance.

[kaya]

I designed some blades. Although neither of them got produced:-), I sort of know the procedure. Tell me what you need to know

[davidwilcox]

Try downloading Qblade

[tareqkh]

Qblade can't design blades but rather you can test a blade...

[CFD-Lover]

Originally Posted by kaya

I designed some blades. Although neither of them got produced:-), I sort of know the procedure. Tell me what you need to know

Hello Kaya,

Thank you very much for your reply. I have a blade with a radius of 0.29 m and hub radius as well of 0.066 m. I want to design this blade at wind speed of 6 m/s and tip speed of 4.5.The blade has three different airfoils; NACA 63-218, 215, 212 respectively from root to tip. What is the optimum blade that you could come up with? Appreciate you hospitality!

Thanks in advance,

[kaya]

I personally like keeping things simple so maybe picking one airfoil is better considering the rotor is rather small. I'd check the glide ratio vs aoa and Cl vs aoa curve to pick a sweet spot that Cl is far from the stall and glide ratio is high. When you define the angle of attack, you now can find the twist distribution by assuming an axial induction. When you fix your tip speed ratio, you can 'sort of' get the twist distribution by saying that you'll have an optimum axial induction say 0.3

At this stage you have a blade with twist but not the chord distribution. To find this I'd first fix my max chord value at the section closest to the root and put a linear change towards the tip as an initial guess. I'd, after, put that blade into a BEM solver (I don't know what qblade is but I guess thats what it does, or you can code yourself ~ 50-100 matlab lines.) and check how far you're from the axial induction that you aimed, and adjust the chord accordingly to get as close as it gets.

I can suggest you to look at "wind energy handbook" where they have simplified equations for chord and also twist distribution for an optimum rotor. This will make your life easier

If you're planning to produce the blade I'd take that into account in design. Like, if you're going to 3d print it, I think I'd use 18 foil all the way, also if you're not gonna have a pitch, and your generator is going to work at fixed speed, thick foils tend to transition to stall smoother.

hope it helps.

[CFD-Lover]

Originally Posted by kaya

I personally like keeping things simple so maybe picking one airfoil is better considering the rotor is rather small. I'd check the glide ratio vs aoa and Cl vs aoa curve to pick a sweet spot that Cl is far from the stall and glide ratio is high. When you define the angle of attack, you now can find the twist distribution by assuming an axial induction. When you fix your tip speed ratio, you can 'sort of' get the twist distribution by saying that you'll have an optimum axial induction say 0.3

At this stage you have a blade with twist but not the chord distribution. To find this I'd first fix my max chord value at the section closest to the root and put a linear change towards the tip as an initial guess. I'd, after, put that blade into a BEM solver (I don't know what qblade is but I guess thats what it does, or you can code yourself ~ 50-100 matlab lines.) and check how far you're from the axial induction that you aimed, and adjust the chord accordingly to get as close as it gets.

I can suggest you to look at "wind energy handbook" where they have simplified equations for chord and also twist distribution for an optimum rotor. This will make your life easier

If you're planning to produce the blade I'd take that into account in design. Like, if you're going to 3d print it, I think I'd use 18 foil all the way, also if you're not gonna have a pitch, and your generator is going to work at fixed speed, thick foils tend to transition to stall smoother.

hope it helps.

Hello Kaya,

I really appreciate this great discussion. According to your comment above, I did try to generate the blade for the airfoils sets FFA 30, 24, 21. I don't know why am getting the chord length is greater than the rotor radius.

Run.xls

As you can see in the excel file, the chord is bigger than the rotor radius.

Thanks in advance for your kind help,

[kaya]

I am not sure what that excel file does.

[CFD-Lover]

Originally Posted by kaya

I am not sure what that excel file does.

The excel file is my result after optimizing a blade of a radius of 0.29 m and hub radius of 0.066 using the airfoil FFA for the thicknesses 30%, 24%, and 21%. However, as you can see, the chord length is so big compared to the radius of the blade i.e. 0.29 m. I hope that you understand the excel file now.


Picture of the blade

Untitled.jpg

How would you design it?

Best,

[kaya]

I am still not sure what that excel does to give a chord distribution output, I think neither you're. If its not something you made, I'd suggest you to get a BEM solver somewhere or code yourself up. You can follow the wind energy book from Martin O.L. Hansen, the stages are explained there in a very simple way. You can also have a look to the "wind energy hand book" to have a shortcut to the chord distribution, as I told you before. However, if that excel file is sth you made, tell me how do you optimize the chord, based on what, then I can suggest you what you should change or hopefully I can come up with some theories where your error might be.

[CFD-Lover]

Originally Posted by kaya

I am still not sure what that excel does to give a chord distribution output, I think neither you're. If its not something you made, I'd suggest you to get a BEM solver somewhere or code yourself up. You can follow the wind energy book from Martin O.L. Hansen, the stages are explained there in a very simple way. You can also have a look to the "wind energy hand book" to have a shortcut to the chord distribution, as I told you before. However, if that excel file is sth you made, tell me how do you optimize the chord, based on what, then I can suggest you what you should change or hopefully I can come up with some theories where your error might be.

Originally Posted by kaya

I am still not sure what that excel does to give a chord distribution output, I think neither you're.

Thank you for the quick reply. I am using a code written by NREL, which outputs the previous Excel file based on the airfoil sets and hub and rotor radius.

Originally Posted by kaya

If its not something you made, I'd suggest you to get a BEM solver somewhere or code yourself up. You can follow the wind energy book from Martin O.L. Hansen, the stages are explained there in a very simple way. You can also have a look to the "wind energy hand book" to have a shortcut to the chord distribution, as I told you before.

Have you written any code based on Martin O.L. Hansen BEM?

Originally Posted by kaya

However, if that excel file is sth you made, tell me how do you optimize the chord, based on what, then I can suggest you what you should change or hopefully I can come up with some theories where your error might be.

Again, the excel file is a result of the NREL code, which is based on BEM. I am asking for help since I am not a blade expert. I want to design this blade for a validation project. If you don't want to help, I can live with that.

Best,

[kaya]

chill

I don't think you were expecting me to try to understand what that excel file does and explain that to you, or were you? If that's what you were expecting, you will need to live without that.

If its from NREL, I bet there is a manual or a report etc., I think they are very good at bookkeeping / writing tech. reports.

Yes, I wrote a BEM by using that book.

Since I am neither a teacher nor an author, I don't think I can do any better than these books on explaining the whole subject, so I don't see the point me spending the time here starting from scratch. And since you haven't given me what you don't know/what you can't understand, all I can say is to direct you to some sources. Like it or not

best of luck