I to design this turbine blade

[T C]

TL;DR Summary

I need help from others here regarding designing a turbine blade.

Given above is a rough model of what I want to make. This is in fact a turbine that will be placed in airlfow of 65-70 m/s velocity. I want to make it by using a 3D printer. But I want to use the best design of the blades that will give me highest output out of this airflow. Can anybody tell me how to design blades (like as shown in the photo) so that the design can be fed to a 3D printer. The gap between two rings for my design is 3 cm and the width of the turbine would be 4 cm.

 

[Baluncore]

The gap between two rings for my design is 3 cm and the width of the turbine would be 4 cm.

Is that 4 cm width or depth? Is it the chord length of the blades 4 cm?

It looks like you will need to make 9 separate blades. Those will be mounted between the two steel ducts. Or will you fabricate the entire spinner as a single unit?

Each blade will be a 3 cm wide section of airfoil with a chord length of 4 cm. Because the blades are short they will have very little twist.

 

[T C]

I just want to make/print the blades and put those in the still frame later. And this is a comparatively shorter model. The model I want to make has 19 cm external and 16 cm internal radius.

 

[anorlunda]

But I want to use the best design of the blades that will give me highest output out of this airflow. Can anybody tell me how to design blades (like as shown in the photo) so that the design can be fed to a 3D printer.

Wow. That is a particularly difficult problem in computational fluid dynamics. Maybe someone can recommend a book, or a public domain software package. Be prepared to spend lots of time and effort to compute the answer.

 

[Baluncore]

The blade has an airfoil profile that is determined by inner and outer radii. You need to fix the ratio of those radii, or redesign from scratch. You also need to fix the length of the airfoil chord. You will also need to specify turbine RPM when airflow is 65-70 m/s velocity.

Is this a turbine that rotates, or a stator in a duct? There will need to be a dome on the upstream side and a cone downstream, to keep the flow clean. The turbine does not exist in isolation.

 

[T C]

Is this a turbine that rotates, or a stator in a duct? There will need to be a dome on the upstream side and a cone downstream, to keep the flow clean. The turbine does not exist in isolation.

This is not a stator but rather a turbine. I have mentioned it at the start. Can't understand why a dome and cone is needed to keep the flow clean.

 

[Baluncore]

Wow. That is a particularly difficult problem in computational fluid dynamics.

I hope there is an optimum design and data for a model airplane wing, with similar scale, profile and airspeed.

 

[Baluncore]

Can't understand why a dome and cone is needed to keep the flow clean.

Look at the compressor at the front of a jet engine. There is a dome that keeps the flow entering the compressor clean. The blades will work efficiently only if there is laminar flow over the blade airfoil.

 

[T C]

Just consider that the flow is laminar without a dome. I mean there are ways to make a laminar flow (that I don't want to discuss here) without a dome. I am only concerned here about the design of the blades and not in any other factor.

 

[T C]

Just found this design from the link. But not sure whether any 3d printing company can make what I want to from this design or not. Kindly help!

 

[russ_watters]

This didn't get a response, so I'll bump it and expand:

You will also need to specify turbine RPM when airflow is 65-70 m/s velocity.

If you want higher rpm you get lower torque and vice versa. This should be optimized for what is being driven.

 

[russ_watters]

View attachment 263002
Just found this design from the link. But not sure whether any 3d printing company can make what I want to from this design or not. Kindly help!

You could probably send that to someone and just say you want that shape 3cm long and extruded 3cm high and get something you can use.

 

[T C]

To whom? I don't know such an expert for now.

 

[T C]

Can anybody here at least what this type of wings are named as? Such kind of wings were used in early aircrafts when the velocity of planes are low. Such kind of wings produce the maximum lift in comparison to othe kind of wings. But it also produces maximum drag that limits the velocity of the plane.

 

[russ_watters]

To whom? I don't know such an expert for now.

Google turns up lots of hits for on demand 3d printing. Research, pick one and talk to them.

 

[T C]

I have already searched it. But 3D printers require further details. Like the frontal angles, tip angle, curveture radius etc.

 

[russ_watters]

I have already searched it. But 3D printers require further details. Like the frontal angles, tip angle, curveture radius etc.

Most probably just want a CAD file. Do you have access to CAD software (there are free/open source ones...)? Get it, draw what you want them to make, and send it to them.

Honestly, I don't see/understand the problem here. People do this kind of thing all the time.

 

[anorlunda]

They are called buckets, or vanes, not wings.

@Baluncore came closest to what you need. It is analogous to the turbine section of a jet engine.

If you search around online, or perhaps in junkyards, you might find an affordable vane to buy and copy. You might also find a drawing showing the cross section.

But how close this will come to "best design" for your application is guesswork without the detailed calculation. Designs like that don't scale well in size or air velocity. It is up to you decide how confident you need to be that what you have is "best."

Even the number of vanes is not guaranteed to be best. Your picture shows 9.

 

[T C]

Honestly, I don't see/understand the problem here. People do this kind of thing all the time.

i just want to know a few little things. The necessary data so that I can make it from a 3D printer and the name of this type of wings. Nothing else!

 

[russ_watters]

But how close this will come to "best design" for your application is guesswork without the detailed calculation. Designs like that don't scale well in size or air velocity. It is up to you decide how confident you need to be that what you have is "best."

Even the number of vanes is not guaranteed to be best. Your picture shows 9.

This is the sort of thing one might do a master's thesis on. It isn't easy or quick (I know you are just pointing out the variables...). My advice for the OP is to start by just making *something* that works, as a starting point. Right now the path seems likely to yield nothing but analysis-paralysis, but if he just *does it*, he'll at least end up with a functional turbine. If he sets that criteria as a goal, it's pretty much impossible to fail.

 

[Baluncore]

A very common airfoil is still the Clark Y. Just draw something that looks like that and it will work.
https://en.wikipedia.org/wiki/Clark_Y_airfoil

The problem with 3D printing an airfoil will always be thinning the trailing edge.

Just found this design from the link. But not sure whether any 3d printing company can make what I want to from this design or not. Kindly help!

Those thick high-camber airfoils had the highest lift, but also had very high drag. They were the German style from Gottingen University 100 years ago. The thickness gave more rigidity for early monoplane wings, but greatly reduced the maximum airspeed.

 

[Baluncore]

There are a couple of 31 Mbyte files here that help identify different profiles.

Parametric Airfoil Catalog, Part I, Archer A18 to Göttingen 655
http://liu.diva-portal.org/smash/get/diva2:680077/FULLTEXT02.pdf

Parametric Airfoil Catalog, Part II, Göttingen 673 to YS930
https://www.diva-portal.org/smash/get/diva2:680088/FULLTEXT02.pdf

 

[DrClaude]

There is a database of airfoils where you can get data files with the coordinates of the profile:
https://m-selig.ae.illinois.edu/ads/coord_database.html

It includes the Clark Y that @Baluncore mentioned.

 

[T C]

I have chosen one. Kindly see the attached file. It's a high camber more lift type of wing used long ago in low speed aircrafts. Whatsoever, I need just one more help. I can't understand the table 177 given in the attached file. Need help to understand it.

 

[russ_watters]

I have chosen one. Kindly see the attached file. It's a high camber more lift type of wing used long ago in low speed aircrafts. Whatsoever, I need just one more help. I can't understand the table 177 given in the attached file. Need help to understand it.

Do you understand any of it? Those are just geometric properties picked-off of/interpreted from figure 137.

 

[T C]

Some, not all. Especially those at the top i.e. Maximum Thickness and Maximum Camber part. Rest is more or less clear.

 

[russ_watters]

Some, not all. Especially those at the top i.e. Maximum Thickness and Maximum Camber part. Rest is more or less clear.

They are expressed in % of chord and you can read them straight off the graph: 5.9% is 0.059 on the graph. And the X-coordinate is given at 0.21. In other words, if the chord length is 100 cm, the maximum thickness is 5.9 cm.

 

[cjl]

Is this going to be placed inside a duct, or is it going to be in free airflow? Basically, is the flow constrained to go through the turbine, or can it also flow around it? That will significantly change the design considerations here.

 

[T C]

Is this going to be placed inside a duct, or is it going to be in free airflow? Basically, is the flow constrained to go through the turbine, or can it also flow around it? That will significantly change the design considerations here.

This will be placed inside a duct. And, by the way, can anybody tell me the "critical angle of attack" and the lift to drag ratio for that speicific angle for such a wing type?

 

[Baluncore]

Try this link; http://airfoiltools.com/airfoil/details?airfoil=ah7476-il

 

[T C]

What would be the Reynold's number if it's simple air at 1 barA pressure and at arouind normal temperature?

 

[jrmichler]

A good search term is Reynolds number. Two good hits are:

For a general overview: https://en.wikipedia.org/wiki/Reynolds_number
For an airfoil: http://airfoiltools.com/calculator/reynoldsnumber

Note that you will have one Reynolds number for the flow through the duct, and a different Reynolds number for one of the fan blades. Which is why it's a good idea to carefully read through a general overview of the Reynolds number before jumping to a specific calculation.

 

[cjl]

OK. What are the flow conditions in the duct? Is there a significant pressure ratio from the inlet to the outlet? What kind of flow velocity are you expecting?

 

[enkii57]

Summary:: I need help from others here regarding designing a turbine blade.

View attachment 262979​

Given above is a rough model of what I want to make. This is in fact a turbine that will be placed in airlfow of 65-70 m/s velocity. I want to make it by using a 3D printer. But I want to use the best design of the blades that will give me highest output out of this airflow. Can anybody tell me how to design blades (like as shown in the photo) so that the design can be fed to a 3D printer. The gap between two rings for my design is 3 cm and the width of the turbine would be 4 cm.

Blades are 35.5° relative to the incoming wind, I assume?

 

[T C]

Blades are 35.5° relative to the incoming wind, I assume?

For this model maybe, but that's not exactly what I want to made. The blade angle is different for my case.

OK. What are the flow conditions in the duct? Is there a significant pressure ratio from the inlet to the outlet? What kind of flow velocity are you expecting?

The velocity is around 66.5 m/s.

 

[Baluncore]

The velocity is around 66.5 m/s.

It is going to be quite noisy at 66.5 m/s = 240 kph = 150 mph.

 

[jrmichler]

If I understand correctly, you want to place a turbine in a duct. The air in the duct will drive the turbine. The air in the duct is moving 66.5 m/sec = 218 ft/sec. The turbine will be 19 cm outside radius = 15 inches diameter. The turbine will be 16 cm inside radius = 12.6" inside diameter. The total air flow will be through the 12.6" ID, 15" OD annulus.

Now for some calculations:
A 15" diameter duct flowing at 218 ft/sec = 16,000 CFM.
The velocity pressure at that speed is 10.6" w.c.
The duct has area 1.23 ft^2.
The annulus has area 0.36 ft^2.
The air velocity through the annulus will be 218 ft/sec X 1.23 / 0.36 = 743 ft/sec.
The velocity pressure in the annulus will be (neglecting compressibility) 123 in w.c. = 4.5 PSI.
If we assume that the turbine blades are oriented 30 degrees to the airflow at the outer radius, the tangential velocity of the turbine will be 372 ft/sec, or 5700 RPM.

Conclusions and things to be aware of:

1) Installing this turbine in that duct will create a very large pressure drop due to the reduced flow area caused by the center area blockage. A carefully designed downstream section can reduce, but will not eliminate, that pressure drop.

2) As mentioned above, the entrance needs a streamlined nose cone. Lack of a properly designed nose cone will further increase pressure loss.

3) A plastic rotor of this size spinning almost 6000 RPM will explode due to centrifugal force.

4) Any power drawn from a turbine will cause pressure drop. If the system can tolerate that pressure drop, you would be better off to reduce the system pressure. The power saved from reducing system pressure will be greater than the power generated by the turbine.

 

[T C]

If we assume that the turbine blades are oriented 30 degrees to the airflow at the outer radius, the tangential velocity of the turbine will be 372 ft/sec, or 5700 RPM.

How you have calculated the rpm?

The annulus has area 0.36 ft^2.

How you have calculated the annulus?

 

[Baluncore]

How you have calculated the annulus?

“The total air flow will be through the 12.6" ID, 15" OD annulus”.
Di = 12.6”; Ri = 6.3”; Do = 15”; Ro = 7.5”.
Area = Pi * ( Ro^2 – Ri^2 ) = 52.025 sq inches.

How you have calculated the rpm?

"The airspeed in the open duct is 66.5 m/s".
The duct has an area of Pi * 7.5 * 7.5 = 176.7 sq inch.
But the middle is blocked = Pi * 6.3 * 6.3 = 124.69 sq inch.
Leaving 176.7 - 124.69 = 52.0 for the airflow.

The airspeed must increase through the constriction of the turbine throat.
To; 66.5 * 176.7 / 52.0 = 226.0 m/s.
A blade at 30° to the airflow will move sideways at; 226.0 * Tan( 30° ) = 130.5 m/s.
The crude average diameter of the duct is about ( 12.6 + 15 ) / 2 = 13.8”
The mid-blade circumference of the turbine is Pi * 13.8=43.354” =1.1 m.
It will do 130.5 / 1.1 = 118.62 revs per second; = 7117. RPM.

 

[russ_watters]

If I understand correctly, you want to place a turbine in a duct. The air in the duct will drive the turbine. The air in the duct is moving 66.5 m/sec = 218 ft/sec. The turbine will be 19 cm outside radius = 15 inches diameter. The turbine will be 16 cm inside radius = 12.6" inside diameter. The total air flow will be through the 12.6" ID, 15" OD annulus.

Now for some calculations:
A 15" diameter duct flowing at 218 ft/sec = 16,000 CFM.
The velocity pressure at that speed is 10.6" w.c.
The duct has area 1.23 ft^2.
The annulus has area 0.36 ft^2.
The air velocity through the annulus will be 218 ft/sec X 1.23 / 0.36 = 743 ft/sec.
The velocity pressure in the annulus will be (neglecting compressibility) 123 in w.c. = 4.5 PSI.

The velocity really needs to be clarified by the OP because the way I first interpreted it, the 66.5 m/s was through the turbine, not in the duct ahead of it. If your interpretation is correct, that's a big problem.

That airflow at that velocity is an airflow power of 200 kW for the kinetic energy alone (not including compressibility or the static pressure losses through the ductwork). An industrial fan for this purpose (if you can even find one) will cost many tens of thousands of dollars and the system requires real engineering design, not just guesswork and back-of-the envelope calculations.

This project is not achievable on the level of a home-made, non-expert/tinkerer experiment.

 

[T C]

I have clearly stated at the starting post that the velocity of the flow touching the blades is 66.5 m/s. Most probably it's my fault that I have misinterpreted what is meant by a duct.

 

[jrmichler]

This is in fact a turbine that will be placed in airlfow of 65-70 m/s velocity.

The velocity is around 66.5 m/s.

Based on these two quotes, my assumptions stand because standard practice is to report average duct velocity, not peak velocity around obstructions. Even at the lower velocity through the turbine, the rotor RPM at the 35.5 degree blade angle will be over 2500 RPM. I have not calculated the stresses, but it is unlikely that a 3D printable plastic rotor of your dimensions will survive that. Don't forget to calculate deflection and creep.

As side note, small airplane propellers run at about 2500 RPM. The C172 I flew yesterday cruises nicely at 2400 RPM. Those propellers are made from aluminum, wood, or carbon fiber. Not thermoplastic.

As others have said, you need the nose cone to get smooth air flow into the turbine. Smooth air flow is necessary for proper operation.

And Point #4 in Post #37 still stands, with one addition. The total pressure drop is proportional to the power generated (divided by efficiency) plus the center section obstruction drag plus additional drag due to the turbine mounting system.

 

[T C]

It's my choice. Hope it will work. Want to know others opinion.

 

[cjl]

Plastic should withstand that RPM just fine, given the dimensions stated (and an appropriate plastic selection). There's a big difference between a C172 prop at nearly 2m in diameter and a little turbine a few tens of centimeters across.

 

[cjl]

That airflow at that velocity is an airflow power of 200 kW for the kinetic energy alone

Are you sure? I get 1/10 that, though I could be making a mistake here (it is rather late and I did the math quickly).

 

[russ_watters]

I have clearly stated at the starting post that the velocity of the flow touching the blades is 66.5 m/s. Most probably it's my fault that I have misinterpreted what is meant by a duct.

The wording in the OP isn't exactly clear and we haven't seen a drawing, which would make it crystal clear. Essentially, the annulus/nose cone could be considered part of the duct or part of the device, but I agree with @jrmichler that it would be more common to see it as part of the device. Heck, without a complete picture or diagram we're still basically just guessing that there's a nose cone on it and that air isn't flowing through the middle ring.

Are you sure? I get 1/10 that, though I could be making a mistake here (it is rather late and I did the math quickly).

Mixed-units are a pain here, but here's what I did (and I'm too lazy to write-out all the unit conversions and calcs, but let me know if you can't identify one):

16,000 CFM / (3.28³ * 60) = 7.56 m³/sec = 9.26 kg/sec
743 ft/s = 226.5 m/s
KE/s = .5mV² = 237 kW

But that's not the OP's intent anyway. He's after this:

66.5 m/s through 52 in² is 2.23 m/s ³/s = 2.73 kg/s
KE/s = 6.0 kW

I think I did that right...

Again, this doesn't include static pressure losses in the ductwork system or, of course, the power output of the turbine (which also manifests as a static pressure loss) and efficiency of the fan. If we double or triple that, we're starting to run up against the limit of residential electrical supply as well.

It's my choice. Hope it will work. Want to know others opinion.

You're fortunate to have several professional engineers helping you through this, and while it is your choice, keeping us guessing doesn't help your chances. Near as I can tell, you haven't started to address what the turbine is spinning and what is moving the air through it, but I suspect you have some ideas you haven't yet shared. Those choices/ideas will have a huge impact on whether this project will "work".

Simply put, the more real/rigorous effort you put into this, the better your odds of success will be.

 

[T C]

Thanks for everyone for their valuable suggestions. I have just one more question. It's a known fact that lift force is lift factorXarea. Now, how is the area calculated? For a strainght rectangular shaped wing, is it chord lengthXwidth?

 

[cjl]

Yes, but that's not necessarily helpful when designing a turbine. Because the shape of the turbine actually substantially impacts the inflow conditions, you can't assume that just doubling the area will double the extracted power, for example.

 

[T C]

Can you explain why?

 

[Baluncore]

Can you explain why?

The blades slice the air in a helical pattern. There is no advantage in slicing air that has already been sliced by another blade.
The surface drag or whetted area of a wider airfoil is greater.
https://en.wikipedia.org/wiki/Blade_solidity