Big modern S rotor

[Pierre159]

Hello all,

i have choose to try to build a big savonius rotor to use as mechanical force, with my low wind  it's well suitable.  i don't want to build an old school savonius rotor i think it's better to use this form (rahai) https://www.researchgate.net/publication/313625566_Lift_and_Drag_Forces_of_a_High_Efficiency_Airfoil_With_an_Embedded_Rotating_Cylinder
this rotor have been well studied optimised all the Cp that you can find on this rotor is one of the best savonius and permit to have  a power average 24h/24h in my conditions

this rotor save money because with the same drum i can build a larger rotor than the old sovonius type. with 1 drum you can build a 1.50m rotor or with 2 a 3.0m.   That turns out well  i have more than 6 drums available,  i can stack rotor by 3 like here:
https://www.motherearthnews.com/sustainable-living/renewable-energy/savonius-super-rotor-zmaz74zhun/

i want to have your opinion on the chassis that i have to make to hold this 3 mx 2.6? (i don't want to go high rotor inclusive 5/6m)
wich diameter of the main axis? are you using full axis or a pipe as axis?
do you think it's important to make a disk 3m plywood between each step?

[Astro]

 I came up with my design, by first laying out some goals. How much power was acceptable. I mean yeah the first week I wanted to build this huge machine in my yard. Well a little research and I was way way over $1,000 just for the magnets. So then I decided to lower how much power was acceptable. What I mean is I could not afford to build a huge machine and a tiny one did not seem like it was worth the trouble.
 Once I had an idea on that, I started coming up with other things I wanted from the machine. How many rpm and stuff. But I worked with electricity most of my life, so that part of the project came much easier for me.
THEN I read everything I could find on many different designs to find which one came the closest to being able to do what I wanted the finished product to do, with the height and wind speed available.
Now that I had it narrowed down the different designs a bit, I started watching youtube. I watched the educational stuff on those types and I also watched the ones of people who tried to build them. Obviously some worked better then others, so I paid attention to what was working and why and what was not working and why.
All that plus a lifetime of building things, gave me a pretty good idea on how to move forward in building what I think should work in my yard at the height I am going to put it and with the wind I have available.
 I know that is not the answer you wanted to hear and it is a ton of work. I think I was at it for 6 months or better and many hours a day before I ever even picked up a tool to start building. But....... if that is what it takes me to build something that I hope works, that is the price I had to pay. Now it is just picking up the parts as I can afford and to keep building it. All while knowing that I will most likely change things on it after it is up and going, in an effort to keep making it better and better. But I knew going in, that it is not a project, it is a lifestyle.
 

[Pierre159]

i just ask your idea to make less foolishness...

[Astro]

i just ask your idea to make less foolishness...

And I told you that is not the answer you want to hear. I mean look certain ideas work and are proven to work, but really no 2 wind turbines anyone on this board has made are the same. Some may be close but they are all different.

[MagnetJuice]

You are right Pierre, the Rahai modified Benesh appears to have the highest Cp of any of the Savonius blades. Also the TSR is a little higher for the Rahai.

It has also been demonstrated that 2 blades per bucket are better that 3. And that 2 buckets per system are better than 1 or 3 buckets.



The end plates are necessary to increase efficiency, and that includes a plate between the 2 buckets.

The main thing is that any windmill that you build is going to require an average wind speed of at least 6 m/s. If you don’t have wind, you will be wasting money and time.

Ed

[Adriaan Kragten]

The point with Savonius rotors is that you need a lot of material for the buckets and the end plates. The total area of these sheets is much larger than the swept rotor area. If you would use this material for a slow running HAWT, it will have a much larger swept rotor area and as a well designed HAWT will also have a higher maximum Cp, you will get very much more power from the same amount of material. I estimate that it is about a factor five higher. Another problem for a normal Savonius rotor is that the starting torque coefficient fluctuates strongly depending on the position of the rotor. This fluctuation can be flattened by using a 2-phase rotor but this adds a third end plate.

If you need a rotating vertical shaft which drives a mechanical load with a high starting torque like a positive displacement pump or a grinding mill, you need a 90° transmission in the head if you use a HAWT and this is an extra investment. But if you chose the correct transmission, the head can be turned out of the wind at high wind speeds and so the rotational speed and the thrust are limited. For a Savonius rotor, nothing can be done at high wind speeds and so the rotor and the tower must be very strong which is another reason why a big Savonius rotor is very heavy.

In my public report KD 651 I describe the slow running VIRYA-3.6L2 windmill which has a 90° accelerating transmission and a vertical shaft in the tower and which has a starting torque coefficient which is that high that the vertical shaft can be coupled to a positive displacement pump.

You should be very suspicious if someone claims to have designed a Savonius rotor with a high maximum Cp. Already in 2009, I have researched if I could find reliable measurements for Savonius rotors. The result of this investigation is given in my public report KD 599. Most measurements have been performed in closed wind tunnels and this results in a too high maximum Cp because a Savonius rotor is more sensible to tunnel blockage than a HAWT (see chapter 2.8 ). The reason is that there is only a small flow through the rotor and so a large flow around the rotor. Tunnel blockage results in increase of the wind speed around the rotor and so you will measure a higher maximum Cp than for a rotor around which the wake can expand freely, like you have in open air.

[electrondady1]

hello Pierre,
 i was building 3 bladed drag mills for about 10 years then i discovered the squirrel cage configuration and will use that design from now on .
two and three bladed drag mills are subject to very powerful torque pulses that can result in damage to the mechanism.
what are the dimensions of the the drums?
what material are the drums made from?
the horizontal disks you speak of  are good to retain the vanes of the mill but, because they are horizontal can trap and absorb moisture.
in Canada those disks can accumulate snow and ice and interfere with the efficiency of the device.
 
can you weld ?
if so, i suggest  a locking collar fitted to the central axial and steel angle iron  support brackets for the vanes.

the vanes of the 3 bladed drag mills i built were made from high density polyethylene and were very low mass. the dimensions of the entire  mills was 24"x 48"
 the central axial was made form 5/8" cold rolled steel and i had no problems with them bending  even though i had no top pin  .
if you are stacking the windmill segments i would suggest you go with a 1" solid axle or larger diameter steel  pipe.
you made need to construct a top bearing retainer and run support cables to the ground if you go very high.
good luck

 

[gsw999]

I learned from building one from an oil drum that all vawts I had seen have an inherent design problem , nothing to stop wobble.

[Astro]

hello Pierre,
 i was building 3 bladed drag mills for about 10 years then i discovered the squirrel cage configuration and will use that design from now on .
two and three bladed drag mills are subject to very powerful torque pulses that can result in damage to the mechanism.
what are the dimensions of the the drums?
what material are the drums made from?
the horizontal disks you speak of  are good to retain the vanes of the mill but, because they are horizontal can trap and absorb moisture.
in Canada those disks can accumulate snow and ice and interfere with the efficiency of the devise.
 
can you weld ?
if so, i suggest  a locking collar fitted to the central axial and steel angle iron  support brackets for the vanes.

the vanes of the 3 bladed drag mills i built were made from high density polyethylene and were very low mass. the dimensions of the entire  mills was 24"x 48"
 the central axial was made form 5/8" cold rolled steel and i had no problems with them bending  even though i had no top pin  .
if you are stacking the windmill segments i would suggest you go with a 1" solid axle or larger diameter steel  pipe.
you made need to construct a top bearing retainer and run support cables to the ground if you go very high.
good luck

 I thought a lot about that design myself. For the reasons you pointed out.

[Pierre159]

for astro
it's 55 galons steel drums

the horizontal disks you speak of  are good to retain the vanes of the mill but, because they are horizontal can trap and absorb moisture.
in Canada those disks can accumulate snow and ice and interfere with the efficiency of the devise

i'm agree with that and for diameter 3m it add weight...
what dou advice me to do?

can you weld ?
if so, i suggest  a locking collar fitted to the central axial and steel angle iron  support brackets for the vanes.

i can weld but i don't see really what you want to tell

for adriaan,
i take care to Cp that they tell hare read many studies and some benech rotor have been tested outdoor and i don't dream even if they tell Cp of rahai rotor touch 0.44 in real condition if it's less it will be really much better than the standard savonius.
still true a vawt use more material than the HAWT.
do you have more plan or picture of your virya 3.6L2?

[Adriaan Kragten]

All what is available about the VIRYA-3.6L2 is given in report KD 651 and in other KD-reports which refere to the Polycord transmission (see reference KD 651). Next week I become 75 years old and the time of building wind turbines is over. The only thing I still do is making calculations, present some ideas in KD-reports and react to questions about wind turbines on forums.

[Bruce S]

All what is available about the VIRYA-3.6L2 is given in report KD 651 and in other KD-reports which refere to the Polycord transmission (see reference KD 651). Next week I become 75 years old and the time of building wind turbines is over. The only thing I still do is making calculations, present some ideas in KD-reports and react to questions about wind turbines on forums.

Adriaan;
That is a very nice read (KD-651) However, I'm a little confused by the word "lumber" on page 17 of the report. It is used to mean debris or ??
Congrats on the upcoming anniversary!

Bruce S

[electrondady1]

i would substitute large plastic barrels for the steel barrels you speak about .
these plastic barrels are strong and a fraction of the weight .

to support the barrels i would weld angle iron to the locking collars

[DamonHD]

@Adriaan  75!  Goodness!  Please keep writing the reports and helping people here (and elsewhere)!

Rgds

Damon

[Adriaan Kragten]

All what is available about the VIRYA-3.6L2 is given in report KD 651 and in other KD-reports which refere to the Polycord transmission (see reference KD 651). Next week I become 75 years old and the time of building wind turbines is over. The only thing I still do is making calculations, present some ideas in KD-reports and react to questions about wind turbines on forums.

Adriaan;
That is a very nice read (KD-651) However, I'm a little confused by the word "lumber" on page 17 of the report. It is used to mean debris or ??
Congrats on the upcoming anniversary!

Bruce S

I remember that I found the word lumber in a dictionary when I translated the Dutch word "rommel" but it might have another meaning for native speakers. I mean rubbish floating in the water which can clog the pump if no filter is used.

[MattM]

Adrian,

Where is the tipping point between VAWT and HAWT?  There must be a certain tilted axis where you merge the two.  Where choices in raw surface area and blade width scale increases in energy evenly, regardless of which option you choose.  Of course your rotor would no longer be truly omnidirectional, but it should operate well within most of the front quarter, operate no less than as a VAWT when perpendicular, and would drop off near to zero only when a full 180 degrees out of the line of wind.  Surely there is a tipping point where tilt axis acts like a hybrid of both.

[Adriaan Kragten]

Adrian,

Where is the tipping point between VAWT and HAWT?  There must be a certain tilted axis where you merge the two.  Where choices in raw surface area and blade width scale increases in energy evenly, regardless of which option you choose.  Of course your rotor would no longer be truly omnidirectional, but it should operate well within most of the front quarter, operate no less than as a VAWT when perpendicular, and would drop off near to zero only when a full 180 degrees out of the line of wind.  Surely there is a tipping point where tilt axis acts like a hybrid of both.

I don't understand what you are saying. A HAWT doesn't change into a Savonius rotor if you increase the tilting angle.
To my opinion there is no tipping point in between a HAWT and a Savonius rotor. A well designed HAWT is always much better than a Savonius rotor in terms of the amount of power generated at a certain wind speed if a certain sheet area is used for the rotor. And this is even true if the HAWT has a slow running rotor with a high solidity and so with a high starting torque coefficient. Lets take the VIRYA-3.6L2. This windmill has a 4-bladed rotor with a design tip speed ratio of 2. The blades are made out of sheet size 1250 * 625 * 2 mm. So the total blade area is 3.125 m^2. The swept area of the whole rotor is 10.179 m^2.

Assume that you make a 2-phase Savonius rotor with a diameter of 0.75 m and a height of 1.5 m, so with a swept rotor area of 1.125 m^2. Only for the three horizontal disks you need 1.688 m^2. Assume that the overlap of the buckets is 0.15 m. This means that the bucket radius is 0.225 m and so each bucket needs a sheet of about 0.75 * 0.707 = 0.53 m^2. So for four buckets you need 2.121 m^2. So together with the three horizontal disks, you need totally 3.809 m^2. This is a factor 3.809 / 3.125 = 1.22 larger than for the VIRYA-3.6L2. But the swept area is about a factor nine lower! The maximum Cp of the VIRYA-3.6 L2 is also about a factor 1.6 higher than that of the 2-phase Savonius rotor which means that the generated power at the same wind speed is about a factor 14.4 higher. And this very high factor counts for a total sheet area which is a factor 1.22 larger for the Savonius rotor. So if both sheet areas would be the same, the factor in between the generated power would be about 17.5! In my earlier post I assumed a factor 5 and so this was much too optimistic.

So to my opinion there is only one conclusion and that is to forget Savonius rotors. If you need a rotor with a high starting torque coefficient because you have a load with a high starting torque it is much better to use a slow running HAWT and a 90° transmission in the head.

[Bruce S]

Adriaan;
 Sadly I'm starting to see some of the older "hinged" mills that were showing up even on here. I'll dig into the past stuff and may post it here. They were quickly shot down.

Bruce S

[Astro]

Adrian,

Where is the tipping point between VAWT and HAWT?  There must be a certain tilted axis where you merge the two.  Where choices in raw surface area and blade width scale increases in energy evenly, regardless of which option you choose.  Of course your rotor would no longer be truly omnidirectional, but it should operate well within most of the front quarter, operate no less than as a VAWT when perpendicular, and would drop off near to zero only when a full 180 degrees out of the line of wind.  Surely there is a tipping point where tilt axis acts like a hybrid of both.

 See, I like the way you think. I often find my self wondering about such things as well. There is the old question of is a 6 or a 9 and the answer is well it depends which point of view you have. Perspective is an amazing thing and it can not be bought. Being able to see more than one perspective is rare, so I applaud your question.
 

[MattM]

Betz Law doesn't care whether you go HAWT or VAWT.  Betz law is a function of area rather than volume, therefore your VAWT is dependent only on your height and diameter exposed to the wind at any one time, hence the reason there is no good answer on how many buckets work best.  The maximum available power is always going be a factor of that area, and at most you might have a quarter of useable surface area exposed at a useful angle per rotation, no matter how many buckets you have. 

The HAWT has the same Betz limit, but it requires the angle of the blades to be perpindicular to the flow direction.  Anything less than perpindicular to the direction of flow for a HAWT greatly reduces the surface area, and that will continue to reduce until the area matches the same limits as a VAWT once it is 90 degrees out of phase.  At that extreme the HAWT essentially functions as a VAWT.

Once the VAWT is tilted, to give it pitch, it slowly grows area exposed to the wind.  This is true only if the VAWT aligns so that the axis of the pitch falls exactly perpindicular inline with the airflow.  If the VAWT pitches and turns at the same time, then these factors may balance out and gains from the pitch.  This is also true in the opposite way with respect to a HAWT pitching or turning until it is 90 degrees out of alignment.  So a tilted windmill will function in balance to HAWT and VAWT functions at some point.  It should be a range and it should require two functions, but dependent ultimately on surface area aligned to airflow.  Nothing more, nothing less.

[Adriaan Kragten]

The power reduction of a HAWT because of a yaw angle delta goes much faster than the reduction of the rotor area projected perpendicular to the wind direction. So it reduces much faster than cos delta. This is because the power is determined by the component of the wind speed perpendicular to the rotor plane (see figure 7.1 report KD 35). This results in decrease of the power by a factor cos^3 delta. The formulas for the rotational speed, the thrust, the torque and the power for a yaw angle delta are given in chapter 7 of my public report KD 35.

Already in 1979 we have tested a scale model of the 6-bladed CWD-2740 rotor in the wind tunnel for different yaw angles. This rotor has a design tip speed ratio of 2, so the same as for the VIRYA-3.6L2. The results are given in report R 408 S of the Wind Energy Group of the University of Technology Eindhoven but this report is no longer available. In my public report KD 696, I give an overview of the most important measurements for yaw angles of 0°, 10°, 20°, 30°, 40°, 50° and 60°.

We have checked if the maximum Cp is reduced by a factor cos^3 delta and this is about right. We have also checked the reduction of the starting torque coefficient and it appeared that this coefficient reduces only significantly for yaw angles larger than 40°! So if the starting torque coefficient is more important than the maximum Cp, a considerable large yaw angel is allowed.

[Pierre159]

from kd 651

The Polycord transmission is described in chapter 3 and 4 of KD 653

kd653 is not online?

[Adriaan Kragten]

from kd 651

The Polycord transmission is described in chapter 3 and 4 of KD 653

kd653 is not online?

Report KD 653 about the VIRYA-3.6 has been replaced by public report KD 693 about the VIRYA-3.5. Report KD 651 about the VIRYA-3.6L2 has been modified today such that now the correct reference to KD 693 is used. The Polycord transmission is described in chapter 6 and 7 of report KD 693.

[Pierre159]

Do you have a picture of you polycord transmission?
does your virya 3.6L2 can be build in aluminum because foils with 2mm steel it's heavy no?

do you think it's possible to make like here:
https://www.motherearthnews.com/sustainable-living/renewable-energy/savonius-super-rotor-zmaz74zhun/

to add 2 alternator as brake but to be easily disengageable in normal condition?
 

[Adriaan Kragten]

Figure 6 in KD 693 gives a picture of the Polycord transmission. It uses a 15 mm round string and one auxiliary wheel to make that the string direction is exactly tangential at the big wheel on the rotor shaft and at the small wheel at the vertical shaft. The angle of the string around the small wheel is 225° which allows a large torque without slipping of the string along the wheel. The Polycord transmission is also shown in the drawing of the head given in appendix 1 of KD 693.

It is not allowed to use 2 mm aluminium for the blades because this will certainly give flutter in the blades at high wind speeds. Aluminium is also sensible to fatigue. The given rotor with 2 mm steel blades is much lighter than a traditional multi bladed rotor with the same rotor diameter and a design tip speed ratio of about 1. Aerodynamically it is much better because there are no drag losses due to a supporting structure and because the losses due to wake rotation are already rather low for a design tip speed ratio of 2 (see figure 4.2, KD 35).

The link to Motherearthnews is about a 3-phase Savonius rotor with bucket patterns under 60° in stead of 90° for a 2-phase Savonius rotor. The fluctuation of the torque will be somewhat less for 3-phase than for 2-phase but the whole construction is even more complicated. I thought that my earlier calculations show clearly why you should forget Savonius rotors but if you want to continue, it is your choice. They also use a string to drive the generator with an accelerating gear ratio but as all shafts are in parallel to each other, one can use a V-belt or a poly V-belt and it isn't necessary to use a round string. 

[Adriaan Kragten]

I have tried to understand the original report for which the link is given in the first post. It tells about computer simulations for different angles of attack of a strange curved airfoil with an embedded small cylinder close to the end of the airfoil to prevent stalling of the flow at that point of the airfoil. This cylinder has a certain Magnus effect and one has tested this effect for different rotational speeds of the cylinder. So to get this Magnus effect, the cylinder has to be rotated very fast! How would you realize this if the airfoil is used in a Savonius rotor?

The report doesn't give real wind tunnel measurements for this airfoil with embedded cylinder mounted in a Savonius rotor. So the idea that using this airfoil in a Savonius rotor will result in a Savonius rotor with a higher maximum Cp than a normal Savonius rotor with half cylindrical buckets is a wishful dream.

[MagnetJuice]

Yes, those rotating cylinders embedded on the blades are intriguing.

They must be mounted to the blade using small ball bearings. There could also be tiny wind catchers on the cylinders to help get them rotating.

Ed

[MattM]

Seems like you could create a simple wheel-driven pulley system to power your cylinders.  There would be a pulley on your magnus cylinder and a pulley on your fixed center shaft.  As the outer pulley orbits as the array rotates around the central pulley wheel's fixed location it would drag, turning the cylinder.  Fine for lower speeds, but lots of torsion on the center shaft as rotational speeds increase.

[Adriaan Kragten]

Yes, those rotating cylinders embedded on the blades are intriguing.

They must be mounted to the blade using small ball bearings. There could also be tiny wind catchers on the cylinders to help get them rotating.

Ed

These cylinders must rotate very fast to be effective. If you want to spin them by wind catchers, you use a drag machine as propelling force and a drag machine always runs much slower than the relative wind speed at that place of the airfoil. So this won't work. Any Magnus rotor has to be driven by a separate power source and this makes the whole system very complicated.

[MattM]

Adrian, why would you use a power source when you already have the rotational forces?  If you have a fixed pulley, then orbit another pulley around it, you impart rotation in the orbiting pulley.  The desired direction of the rotation decides whether you use the belt normally or in a figure 8.  The relative rotational rate depends on the sizes of the two pulleys.  Torsion twist is obviously a concern, so the central shaft would need to be relatively beefed up.  The biggest limiting factor is the start up wind speed is higher for obvious reasons, but once in motion the magnus cylinders should act like flywheels to help stabilize the rotation of the main rotor.  Keep it simple, (and) stupid.

[Adriaan Kragten]

Adrian, why would you use a power source when you already have the rotational forces?  If you have a fixed pulley, then orbit another pulley around it, you impart rotation in the orbiting pulley.  The desired direction of the rotation decides whether you use the belt normally or in a figure 8.  The relative rotational rate depends on the sizes of the two pulleys.  Torsion twist is obviously a concern, so the central shaft would need to be relatively beefed up.  The biggest limiting factor is the start up wind speed is higher for obvious reasons, but once in motion the magnus cylinders should act like flywheels to help stabilize the rotation of the main rotor.  Keep it simple, (and) stupid.

I argued against the idea to use wind catchers to rotate the embedded cylinders. That isn't possible because the outside surface of the cylinders has to move much faster than the relative wind speed if the cylinders should work as a Magnus rotor. Theoretically it might be possible to get this high rotational speed by an accelerating transmission from the main shaft but that will make the whole idea even more stupid.

[MattM]

Technically speaking your Magnus effect is a product of air velocity across the cylinder relative to tangential speed on the outer surface of the cylinder, so unless rotation was tightly regulated to match air velocity then it is not ideal.  So, yes, there is no good 'kiss' solution.  But if you were aiming for a small range of air velocities it could be made to work on the K-I-S-S principle.  It's all about goals.