new axial design multirotor

[MagnetJuice]

Hello leviatan,

If you felt insulted by something that I said, I apologize.

I am finding it difficult to visualize your alternator design, especially how the polarity of the magnets interact with the coils. I wonder if you can make an image of that or take a picture.

By the way, take a look at this website to see if you can find other magnet size that could work better for you.

https://www.magnet4sale.com

Are you using a dictionary to translate from Spanish? I found that https://translate.google.com does a good job.

I was curious about the Schulz turbine that you talked about so I looked it up. I found a test of 4 Savonius rotors that was uploaded by Felipe Mitjans. That is good information.


I also found a 1989 book in German by Schulz of a Savonius with 2-buckets that uses 2-blades for the rotor. That one they use mostly for pumping water.


Yes, I agree with your view of trying different ideas, learning from them and posting the results whether good or bad.

So, I can accept your pink unicorn if you accept my cheap bicycle, OK? 

Ed

[MattM]

Your diagram suggested you had clearance for 50mm rather than 10mm.  If your dimensions are 100x40x10mm, the most important measures are the effective magnetic strength at the surface and thickness of your coil leg.  Three 10mm thick by 40mm wide x 100mm long magnets in a stack seem to be your goal.  If you could go closer to the thickness of your coils, which you suggested is closer to 50mm, then you can drop from the 100mm length to 20mm length (e.g. 20x50x50 overall) for equivalent magnetic volume at a 25% higher magnetic force at the surface.  By keeping the magnet on the outer diameter of your available circumference, the greater the relative velocity the magnet moves over the coil at the same frequency.  Your geometry is therefore working for you in the same space.  Like someone said earlier, its how quickly the rate of change in magnetic directions that matters.  Magnets located closer to the axis point may have the same frequency, but the rise and fall of the magnetic direction is effectively longer over time because your magnets are still interacting across so much of the arc.  By using shorter, wider magnets you would have stronger magnetic forces (located on the outer limits of your diameter) across that same arc.  This is why people suggest a simpler axial rotor design that can focus on fewer, stronger magnets.  You are effectively an axial design, too, just using a different technique with multiple stators.  Nothing wrong with that.  People are just trying to explain how to make slight changes for a better experience.

[leviatan]

No, you understood wrong all the positions. Dont worry, the next week i will do the test of one coil, and i will take photos in the lathe. About dictionary, no i not use, and i know i should. About schulz i read that specifically article and hundreds of others. But the conclusiones of theys i not agreed... the way to do the tests and the size of the samples cause a huge diference with the behaviors of a wind turbine in the real world.
Because its clear the hawt are the most efficient designs, no body took seriously one or two years to do a test with models ar real scale of diferent vawts, because dint exist so much chances to got comercial profit of designs that use 10 times more materials than the hawts to produce the same ammount of current.

I read about a place in denmark where several kinds of vawts were tested by one or two years, and no one got near of the efficience expected.  Inclusive with that previous studies, Im not convinced about the advantage of two buckets and 2 stages vs the 3 buckets only one stage.
My dream would be a schultz rotor twisted, but a mould to do that is very complicated, my límit is the aluminum profile that i need to produce to hold the poliprhopilene boards, i will not invest more than that in the schultz design.

The last point for me is: do you know some video of one savonius twisted or not of comercial models producing something??? Are beauty to see but if theys produce something (inclusive so far of the predicted) should have some video proofs.
For the hawts indepents if are home made or comercial models you can found a lot of videos with modest or big production according to the sizes and perfection of the designs.
But for vawts you cant find anyone producing at least 30 watts in a tester.
I reach 130 watts and burned 7 pieces of 12v position lamps of car with a wind of 20k/h average and 25 k/h for 2 or 3 seconds.

Then i can read a lot ( and i continúe doing it ) but the practical results are more determinants for me, and for my size of turbine and in the situation of cant invest in twisted designs,  a schultz turbine is my best bet in savonius kind.

Exist a model (savonius and schulz versions) of a company in usa that use a shields and two turbines. At first look should be the best of two world, avoiding a lot of drag with the shields. I made a scale prototype and compared with a normal schultz and the results were sads.

Like Adrián said in earlier post the savonius is a drag device but have a component of lift efect in the returning blade. And the shields kill that efect elsemore of complicate the design adding more parts and weight. 

The schultz design work better that efect of lift in low speeds of wind i guess and for that is my favorite later of test other options.

 
 

[MagnetJuice]

You can build a Schulz like this.

Use 3 blades.



Ed

[MattM]

One of our more recent members did a simple VAWT out of barrel material.  I found videos of it after he posted about his HAWTs.  Gavinfreedomlover or something like that on YouTube.  Pretty interesting example you might look at.

[leviatan]

You can build a Schulz like this.

Use 3 blades.

(Attachment Link) (Attachment Link)

Ed

that is 2 blades design, similar to other two blades of chinese companys. To build that only need the central axis and thread bars to hold the oposite sides of the blades. But for 3 blades you need triplicate quantity of threaded bars. And the design of schulz is diferent at the begin of the blades. The other complication ( not easy to see at first look) the blades not are perfect rectangles, are more like a diamonds, and that took so much material like waste. The chinese Brands cut the blades in several bands to save material.

But i will use standar 1.22x2.44 meters poliprhopylene boards and cut the boards in that shape will loose no less of 50% of the material. I have 30 boards already in my home of my last import,  and with that i would cover the blades material for only 2.5 turbines. If a cut the boards to do the spiral shape, is probably i can cover only 1 turbine area with  the 30 boards.

Then my instintc says me, is better to have a bigger surface área than a more little área with more sophisticated design. Because the probably difference in efficience not is enough to cover the huge  down on size área.

That without says the asemble of the schulz will be so easy, a spiral shape is very much dificult and slow to asemble.
But steticaly the spiral shape is the best, and avoid the use of multiple stages.

When you design something need to decide the equilibrum betwen, cost, efficience, and stetical impact. The balance betwen the 3 features not is easy, and you need to sacrifice something in the way.
If i would have unlimited budget i will choose a spiral in schultz model.  And of course i would try a coreless of 6000-8000 dolars.  But i am concient i cant to produce  a savonius  vawt that works by less of usd 3000 by unit. And that buying materials for severals turbines.
Only the mould for produce the profiles of aluminum at my request, cost usd 1500. And later you need to produce 1000kg of profiles like moq.
Then all is expensive and i try to do something that last very much years with zero maintenance and with modest but sure kw production by year.
All that is complicated to do with so low invests.
And any change on the project that not simplify the design can rise the budget at imposible levels for a green adventure.

By that i am very carefull with the steps and i am getting opinions in the forum, may be some advice can giveme  new ideas and to helpme fixing the design in some aspect. Until the moment i invested around 3500 usd in the project and i calculated to spend others usd 10000 to finish. Is a lot of money for me, and i can trust only in what i can test before.

Like i said previously you can see comercial models of savonius two and 3 blades and a lot of darrieus inspírated designs, but nothing out of that models are being produced in any small or big size until the moment.
That is a important clue about what models have the bigger potential.
I need to go by that way, and límit the design to the tools and budget at my range.

[JW]

What he is pointing out (MattM) is that with 3 blades there is a higher density threshold in atmospheric pressure potential. It can run smoother and have less power-pulse.     

[MagnetJuice]

And the design of schulz is diferent at the begin of the blades.

Can you post a picture of the Schulz turbine?

Ed

[leviatan]

Im continue on vacations. The monday i can post photos of my schulz versión. I used other way to hold the blades.

/////////Https://m.youtube.com/watch?v=r938XAA4xto
That were my first test, with the hoverboards and 15-1 transmisión, later i modified a bit the angle of the blades and worked better. I instaled planetary gearboxes in the last modification and the transmisión part caused a loss of 50% in the end current. I learned the best is no transmisión, or If need to exist can be only two gears, and helicals to avoid undesired sounds.

 That design with thin axis and lateral arms to hold all the structure was to let the easy transport to the shore at 300 meters of my home.
The final design will have only a strong pole like axis and mounted bearings to hold the arms and blades over it, the pole will not be a mobile part, and not add his weight to the turbine blades.
With that design i can reach a very strong structure for to hold the blades, and a low weight of the mobile parts.
I feel 3 blades had enough balance in the spins to avoid the need of a spiral design. With two blades i not believe the spins could be so smoth, by that,  schultz was my choice over others savonius.

[Adriaan Kragten]

But a hawt need average wind speed very much highers than a vawt savonius to produce.

Whether this is true or not, depends on the type of load and the type of Savonius rotor which is used. A normal 2-buckets Savonius rotor has a starting torque coefficient Cqstart which depends very much on the position of the buckets to the wind. It is maximal when the buckets are perpendicular to the wind and almost zero if the buckets are in line with the wind. This problem is normally solved by using two Savonius rotors on top of each other which are turned 90° with respect to each other. This is called a 2-phase Savonius rotor. One can also use buckets with a helical shape but those buckets are very difficult to manufacture. In my report KD 703, I describe a Savonius rotor with four buckets which will have a value of Cqstart which will fluctuate only little. Never use a Savonius rotor with three buckets because the maximum Cp and the optimum tip speed ratio lambda will be much lower than that of a normal Savonius rotor. So lets assume that you use a 2-phase Savonius rotor.

Proper functioning of any wind turbine at low wind speeds is determined by two effects, the starting wind speed and the matching. The starting wind speed depends on the Cqstart of the rotor and on the torque of the load at zero rpm. If the load is a positive displacement pump or a grinding stone, you start with a high load torque at zero rpm and then you need a rotor with a high Cqstart otherwise you will get a very high starting wind speed. But if you use an axial flux generator with no iron in the coils, the zero rpm torque of the generator is only determined by the friction of the bearings and the seal on the rotor shaft. This friction torque is rather low and therefore a high value of Cqstart isn't necessary. The difference in between the rotor torque at a certain wind speed and the friction torque is used to accellerate the rotor. The accelleration depends on the moment of inertia of the rotor. Savonius rotors have a very large moment of inertia and even with a high value of Cqstart, it will take a long time for the rotor to speed up. So if an axial flux generator with no iron in the coils is used, the starting behaviour of a well designed Savonius rotor isn't better than that of a well designed HAWT.

The next point is matching. I have explained matching already several times at this forum and detailed information on this subject can be found in chapter 8 of my public report KD 35. One has to follow the same procedure whether one uses a VAWT or a HAWT. Optimum matching is gained if the Pmech-n curve of the generator for the chosen load is intersecting with the optimum cubic line of the wind turbine at a wind speed of about 5 m/s. It is useless to want optimum matching at a very low wind speed because the power increases to the cube of the wind speed and the power available at very low wind speeds is therefore very low. If the generated electricity is used to charge a battery, charging starts only when the open DC voltage coming out of the rectifier is equal to the battery voltage. So in the speed interval from zero rpm up to this starting rpm, no power is generated. Chosing a very low wind speed for optimal matching results in bad matching at high wind speeds if the wind turbine is used for battery charging. So for this point there is also no difference in between a Savonius rotor and a well designed HAWT.

To my opinion there are only two loads for which the use of a Savonius rotor can be adviced. One is if it is driving a positive displacement pump which is coupled directly to the vertical shaft. The other is to make a Darrieus rotor self starting. However, Darrieus rotors suffer from many disadvantages and I strongly discourage anyone to start with such wind turbines (see report KD 215 and KD 601).

All VAWT's have as main disadvantage that it is very difficult to protect the rotor against high wind speeds. Realise that the maximum wind speed during a thunder storm can become more than 30 m/s. You should calculate the thrust on a Savonius rotor at this wind speed and it will be enormous. Stopping the rotor gives no reduction of the thrust because of the very high solidity of a Savonious rotor. So only for one big storm in ten years, a Savonious rotor must be made extremely strong and so very heavy. No generator is strong enough to load the rotor sufficiently at this wind speed and so at very high wind speeds, the rotor will run almost unloaded. The slightest mechanical or aerodynamical imbalance will then cause enormous vibrations and the whole rotor will be shaken into pieces. So Savonious rotors are dangerous at very high wind speeds and should never be used close to houses!

[Adriaan Kragten]

In my posts I use the dimensionless starting torque coefficient Cqstart (-) and not the starting torque Qstart (Nm) because Cqstart is a certain value for a certain rotor and Qstart depends on the wind speed. The relation in between both units is given by: Qstart = Cqstart * 1/2 ro V^2 * R * A. For a HAWT, A is given by: A = pi * R^2 (m^2). For a Savonious rotor, A is given by: A = 2 * R * H (m^2). ro is the air density (about 1.2 kg/m^3), V is the undisturbed wind speed far before the rotor (m/s), R is the rotor tip radius (m) and H is the height of a Savonious rotor (m).

Another important torque coefficient is the optimal torque coefficient Cqopt. This is the torque coefficient for the optimum tip speed ratio, so for the tip speed ratio for which the Cp is maximal. The ratio Cqstart / Cqopt depends what kind of load can be coupled to the rotor. If the load has a constant torque, like it is the case for a positive displacement pump, one needs a ratio of about 1 to get an acceptable starting wind speed. A well designed Savonious rotor has a ratio larger than 1 so it can be used for a load with a rather high torque at zero rpm. The ratio for a HAWT depends mainly on the design tip speed ratio and is lower if the design tip speed ratio is higher. It is about 0.12 for a 3-bladed rotor with constant chord blades and with a design tip speed ratio of 6 (see figure 3, public report KD 738). The starting wind speed Vstart (m/s), for a certain value of Cqstart and for a certain sticking torque Qs of the load, can be calculated with formula 8.6 of public report KD 35.

[leviatan]

I considered the problem of a large wind storm. If are more extreme than 100k/h the damage to the wind turbine would be the less of the problem. I agree dint exist a load posible to stop the turbine. Then the solution is a construction enough strong.
If the turbine average rpm at 16-20 k/h reach 45-60 rpm ( a large rpm for the size of the rotor) at 5 times more wind speed could reach 5 times more rpm, then would be something like 250 rpm. Not is a crazy speed of rotation to produce a certain destructive force. And in the case of the wind rotor blades got a level of vibration enough to destroy it, the damage probably would be the loose of some prophilene boards. Will not afect the pmg, or the axis pole, in the worst cashes can bend someone of the profiles, and that not are expensives to replace.
And i agree with you, the rotor need some time to acelerate his rpm when the wind speed is increased. By that i remarked the blades need to be strong by liteweight.

If i use steel for the ribons  of the prophilene boards  i got elsemore of problems with the corrosión, and weight exesive. Aluminum profiles with the ideal shape to have a strong structure easy asemble and zero problems of maintenance over hard enviroments is the answer to the problematic of the weight of savonius rotors. I designed a system to hold the blades over pilow block mounted ball bearings. With that system ( not implemented in the prototype because that  one need to be transported by the street) i can put out the equation the weight of the central axis. I can use a steel pole of 145mm diammeter  x3mm wall tick like "axis" to give more than the necesary strenght to the structure and the weight of that pole will not be part of the weight of the  turbine.
I had in account the weackness of savonius, and i got innovative ways to  superate that more scary problems.
That not means the savonius is the best option vs other models of vawt ot hawt, but is the only model that i can produce without being a factory in china and fill my expects on visual impact, sound impact, maintenance, and cost of the parts.

By last , and having in account you are very used to manage the calculations. What is the cp of my prototype if i got 55watts at 16k/h or 80watts at 20k/h. The turbine prototype blades  of the savonius in the video are a rectangle of 2.2meters height x1.70 meters wide.
If i got a cp according to the best savonius i am on the right way.

[Adriaan Kragten]

By last , and having in account you are very used to manage the calculations. What is the cp of my prototype if i got 55watts at 16k/h or 80watts at 20k/h. The turbine prototype blades  of the savonius in the video are a rectangle of 2.2meters height x1.70 meters wide.
If i got a cp according to the best savonius i am on the right way.

The Cp-lambda curve of the rotor of a wind turbine can only be measured accurately in a wind tunnel. This should be a very large closed wind tunnel or an open wind tunnel. A scale model of the rotor should be placed far enough before the tunnel opening of an open wind tunnel to allow the wake around the rotor to expand. The wind speed must be measured far before the rotor by a calibrated pitot tube and must be constant during a measuring range of different rotational speeds of the rotor. The air density ro must also be determined accurately. The mechanical power P of the rotor must be measured which means that the torque Q and the rotational speed n have to be measured. So first the Cq-lambda curve is determined using the formulas for Q and n. The Cp-lambda curve is derived from the Cq-lambda curve because Cp = Cq * lambda. Measuring of the Cp-lambda curve for e real wind turbine in real wind is very difficult because the wind speed is always fluctuating and because one has to measure the wind speed at minimal two times the rotor diameter in front of the rotor. So measurements in real wind always result in a cloud of measuring points around the Cp-lambda curve. So I won't determine the Cp of your rotor for only one or two measuring points especially because I don't know the exact geometry of your rotor and I don't know how you have measured the wind speed and the power.

In my report KD 599 I have researched measured characteristics of Savonius rotors available on the Internet. You should study this report and especially the formulas given in chapter 3. The conclusion is that most measurements have been performed in windtunnels which were too small for the geometry of the Savonius rotor and that therefore tunnel blockage has occured. This means that the measured maximum Cp of the rotor was too high. From the very few reliable measurements (like given in chapter 2.2), it can be derived that the maximum Cp of a 2-phase Savonius rotor is about 0.24 for an optimum tip speed ratio of about 0.9. But the maximum Cp can easily be lower if another rotor design is used.

The mechanical power P (W) of a Savonius rotor is given by: P = Cp * 1/2 ro V^3 * A. A is given by A = 2 * R * H. So P is given by P = Cp * ro V^3 * R * H. Assume that Cp = 0.24 and that ro = 1.2 kg/m^3 (for 20° C at sea level). This gives P = 0.288 * V^3 * R * H. R is the radius of the rotor measured from the axis of rotation. H is the rotor height. With this formula you can calculate the mechanical power for a certain rotor geometry and for a certain wind speed. For the electrical power coming out of the generator, the rectifier and the generator efficiencies have to be taken into account.

The rotational speed n (rpm) is given by: n = 30 * lambda * V / (pi * R). Asssume that the rotor is loaded such that it turns with the optimum tip speed ratio, so lambda = 0.9. Assume pi = 3.1416. This gives n = 8.59 * V / R. With this formula you can calculate the loaded rotational speed for a certain wind speed and for a certain rotor radius. The unloaded tip speed ratio of a 2-phase Savonius rotor is about 1.8 and so the unloaded rotational speed is about a factor 1.8 / 0.9 = 2 higher than the optimal loaded rotational speed.

Checking of the estimated Cp-lambda curve for a real wind turbine in real wind requires a calibrated wind meter placed at the correct position and measuring of the mechanical power of the rotor. If you can measure only the electrical power coming out of the generator, you have to kwow the generator efficiency for every load condition. Because of the fluctuation of the wind speed you will always find a cloud of measuring points. If you take only one optimistic point, you are fooling yourself.

[MattM]

So, basically, its not easy to guess a Cp.

[leviatan]

or if you have the end power measured with the voltmeter, can use the tables with the energy in watts in a meter cubic of air at "X" wind speed and see what percent of that intitial energy you are getting at the end of all process with your area of turbine.
My simplified calculated is
20k/h is around 5,5m/s speed.
Then would be  aprox 90watts by cubic meter of air at 20k/h.
The rotor have 2.2metersx1.70meters= 3,74 square meters of area.
90watts x 3,74= 336 watts in that area of wind.
if i got 60 watts at the end of the process  i need to see how much is the product of 336/60=5,6.

 Around a  18% of the energy on the air at that 20/k/h are obtained like useable current. Then the cp should be in a 18% (im not doing the accounts with sharp precision i know and only had 3 tests, i am taking the numbers of the first and worst) and for me that is enough efficience. And i guess with bigger surface area, and better PMG the overall efficience can be fixed a bit.
But is a good CP number for a home made turbine in savonius kind,  and working in any  winds not only in laminar wind.

[Bruce S]

Adriaan;
Savonious type VAWTs are all but self regulating, doesn't matter 2-blade or 3-blade or n-blade. Built as a true Savonious, when the buckets come around the wind will slow them down. Back in the 70s Mother Earth News and other self-reliant communities went with these for that very reason. To date I have not seen one Savonious style VAWTs blow up in a storm (This comes from seeing ones built across the USA, units built in Belgium, units built in Germany and the Sub-Sarah, so calling them dangerous is a bit harsh. Show me the proof, not via Engineering proof, not numbers , but reports of them blowing up in a high-wind environment. A lot of other types of VAWTS have, the old Egg-beater style certainly did. The Ugrinsky is currently being tested for high-wind stability since it doesn't rely on the buckets to help towards self-regulation.
I'm pretty certain that anyone trying to build one knows they are low-wind and perfectly suited for that, the numbers also show that they are very low in efficiency and down to a certain M/S wind there's not much to gain other than seeing how pretty they are when turning.

Bruce S

[leviatan]

You are coming a bit late to this post bruce, and probably couldnt read all. Adrian is a enthusiast of the efficience and all that not got the maximum efficience dint work for he, and he have his right to think in that way. He not recomend savonius kind of turbines due his low efficience by usd invested vs kw produced. And at the end his lack of enthusiasm for that shape of turbines at the end gave a overall bad conclusions for some points of the design that are in fact the points a favour of savonius.
 
Probably the only problem with savonius are the PMG part, if are so litlle for the power generated, in a big wind storm can be burned (like happen with all the others turbines elsemore).

I believe  when you done the structure  with enough resistance for his size, extreme wind speed dint cause extreme RPM jump and the savonius will survive like gloria gaynor.  Because the savonius works well in average and low wind conditions but in a higher wind storm i can imagine the turbulences and other issues in the low efficience design cant cause a extreme jump in rpm like happen with hawts, or other kinds of VAWTs.
And like you said at the end, is nice to see theys spin in low winds inclusive if not are giving any current .

[Adriaan Kragten]

Adriaan;
Savonious type VAWTs are all but self regulating, doesn't matter 2-blade or 3-blade or n-blade.

Bruce S

I can't believe that. There is no reason why an almost unloaded Savonius rotor won't speed up with the same rate as the increase of the wind speed. There is a Reynolds effect but generally increase of the Reynolds value at high wind speeds results in decrease of the drag coefficient of the used airfoils. It might be that the whole rotor start fluttering at high wind speeds and that this fluttering will finally result in increase of the drag coefficient but to to me this seems no good mechanism to limit the rotational speed.

It will be not very difficult to make a Savonius rotor with a diameter of 1 m and a height of 1 m strong enough. But if you use a rotor with diameter of 3 m and height of 3 m, all dimensions have to be increased by a factor 3 and so the whole rotor will become a factor 27 heavier! So such a rotor will be very heavy. But if you don't believe me, go on with Savonius rotors and spend enormous amounts of money for 1 kWh.

I have calculated the rotational speed for a wind speed of 35 m/s which is the highest wind speed for which thrust calculations have to be performed in The Netherlands. Assume that the rotor is turning almost unloaded with a tipspeed ratio of 1.5. Assume R = 1.5 m. Substitution of these values in the formula for n gives n = 334 rpm = 5.57 rev/s.  Do you think that the rotor will survive this rotational speed if there is some mechanical or aerodynamical imbalance?

[MattM]

Ive seen video where barrel-based Savonius hit 400 rpm+.  With its overhead brace, the atypical winds caused no irrepairable damage but his post-storm analysis definitely found enlongated holes where it mounted the buckets.  So it may have survived with damaged parts, but I doubt it would have survived round 2 or 3.

[leviatan]

Barrel savonius has a short angular momentum, so they rotate MUCH faster than a 3 meter diameter savonius.
Having said this, it is also true that the forces in savonius of a good size are large, but the low rotational speed prevents vibrations that, due to their high TSR, affect other types of vertical turbines.

Lastly, as the Savonius are technically one of the most basic and inefficient models, not many people make them with great care or common sense.

The model that I plan to manufacture is going to use a steel post with a diameter of 150mm and a wall of 3mm as a fixed axis.

The blades will go on bearings mounted on base plates. And the main aluminum arms (of 1.50 meters) that will hold the blades, will be attached to these steel base plates by means of other square steel tubes, as guides.

In this way, a very firm structure can be maintained for the axis of the assembly without affecting the total weight of the moving parts of the turbine.

In the upper part, the bearing will be of the "mounted" type that are built to sustain axial and radial loads at the same time. With a 60mm shaft it is a very robust bearing.
At the bottom there will be two 150mm internal diameter bearings to support only the radial load.

With these considerations I think the system will be very robust and if you are unlucky enough to face a very severe storm, with the maximum 200-250 rpm that it can reach, I don't think any part will be thrown.

[Adriaan Kragten]

or if you have the end power measured with the voltmeter, can use the tables with the energy in watts in a meter cubic of air at "X" wind speed and see what percent of that intitial energy you are getting at the end of all process with your area of turbine.
My simplified calculated is (Attachment Link)
20k/h is around 5,5m/s speed.
Then would be  aprox 90watts by cubic meter of air at 20k/h.
The rotor have 2.2metersx1.70meters= 3,74 square meters of area.
90watts x 3,74= 336 watts in that area of wind.
if i got 60 watts at the end of the process  i need to see how much is the product of 336/60=5,6.

 Around a  18% of the energy on the air at that 20/k/h are obtained like useable current. Then the cp should be in a 18% (im not doing the accounts with sharp precision i know and only had 3 tests, i am taking the numbers of the first and worst) and for me that is enough efficience. And i guess with bigger surface area, and better PMG the overall efficience can be fixed a bit.
But is a good CP number for a home made turbine in savonius kind,  and working in any  winds not only in laminar wind.

The power in the wind Pw is given by: Pw = 1/2 ro V^3 * A. Assume ro is 1.2 kg/m^3 (for 20° C at sea level). This gives Pw = 0.6 * V^3 W/m^2.
20 km/h = 20 / 3.6 = 5.556 m/s. So Pw at 3.556 m/s is 103 W / m^2. You have measured 60 W at V = 5.556 m/s for a rotor with a swept area of 3.74 m^2. So you have measured 60 / 3.74 = 16 W / m^2 for V = 5.556 m/s. So the Cp of your rotor for this measuring point is 16 / 103 = 0.155.

A have assumed for a 2-phase Savonius rotor that Cpmax = 0.24. In chapter 2.3 of KD 599 it was found that the Cpmax of a 2-phase Savonius rotor is about 10 % higher than that of a 1-phase Savonius rotor because of the meandering effect. So Cpmax of a 1-phase rotor is about 10/11 * 0.24 = 0.218. In chapter 2.5 of KD 599 it was found that Cpmax = 0.14 for a Savonius rotor made out of half oil drums. This is rather low and this may be caused by the low Reynolds value or by the fact that the end plates cover only half the buckets and not the whole rotor. So what you have measured seems realistic to me.

My problem with Savonius rotors is not only the low Cpmax but the very large amount of material needed for the rotor and for a direct drive PM-generator.

[Adriaan Kragten]

Advantages of a 2-phase Savonus rotor are that the maximum Cp is rather high (about 0.24) and that the torque fluctuation of the upper rotor is almost flattened by the torque fluctuation of the lower rotor. However, the rotor thrust is still fluctuating. The upper rotor has a maximum thrust if the two buckets are perpendicular to the wind and a minimum thrust if the two buckets are in line with the wind. The thrust acts half way the height of the upper rotor. The thrust pattern of the lower rotor is shifted 90° and the thrust acts half way the height of the lower rotor. The frequency of the thrust fluctuation in Hz is twice the rotational speed of the rotor in rev/s. So the action point of the thrust shifts twice a revolution over a distance of half the height H of the whole rotor. The thrust must therefore be seen as a fatigue load and it can also be seen as a aerodynamic imbalance. The rotor is supported in two bearings at the top and at the bottom and the bearings are a part of a certain tower construction. This tower will have a certain natural frequency and the tower will shake terrebly if the frequency of the thrust fluctuation is the same as the natural frequency of the tower.

So it seems better to use a 4-bucket rotor as described in report KD 703 for the VIRYA-1.45 rotor. The thrust of this rotor will also fluctuate somewhat but it won't shift upwards and downwards. The original VIRYA-1.45 rotor has one plywood horizontal sheet half way the rotor height H to make the rotor simple. However, this will result in a rather low maximum Cp because of tip losss at the upper and the lower side of the buckets. So assume that a horizontal plywood sheet is used at the upper and the lower side of the rotor and that Cpmax = 0.2 for this configuration. The VIRYA-1.45 makes use of four buckets made out of stainless steel sheet size 1000 * 1000 * 1 mm. Each sheet has a mass of 7.8 kg and so the total mass of the stainless steel is 31.2 kg. I havn't checked if 1 mm thick buckets are strong enough but assume that this is the case for a rotor with ply wood end plates at the top and the bottom.

Assume that the geometry of this VIRYA-1.45 is scaled up with a factor 2. Assume that this rotor is called the VIRYA-2.9 as the rotor diameter becomes 2.9 m. So now four stainless steel sheets size 2000 * 2000 * 2 mm are needed. 2 mm thick stainless steel sheet is available is the size 2 * 4 m and so one sheet has to be cut in half. The total mass of these four sheets is now 8 * 31.2 = 249.6 kg. The two plywood end plates, the shaft and the clutch to the generator also have a certain mass and the total mass of the rotor will be at least 300 kg. The swept area A of the rotor is 2.9 * 2 = 5.8 m^2. Assume Cpmax = 0.2. So A * Cpmax = 5.8 * 0.2 = 1.16 m^2.

Assume that the VIRYA-2.9 is compared to a HAWT which also has stainless steel blades. Assume that the VIRYA-2.02 is chosen which is described in public report KD 617. This 2-bladed rotor has tapered cambered blades made out of 2 mm stainless steel. The two blades are connected to each other by a 3 mm stainles steel sheet. The total mass of this rotor, including the hub, is about 5.5 kg. So this is only a factor 0.0183 of the mass of the VIRYA-2.9 rotor! The swept area A of this rotor is pi/4 * 2.02^2 = 3.2 m^2. This rotor has a maximum Cp of at least 0.4. A smaller similar rotor with a diameter of 1.8 m has been measured in the wind tunnel already in 1978 (see report KD 616) and the rotor has a very high maximum Cp and is very silent if it runs at a tip speed ratio of about 6.5. So A * Cpmax = 3.2 * 0.4 = 1.28 m^2. This is even larger than that of the VIRYA-2.9. So the VIRYA-2.02 will produce more power at the same wind speed than the VIRYA-2.9 using a rotor with less than 2 % of the mass! The generator mass will also be much smaller and the VIRYA-2.02 can be protected against a too high rotational speed and a too high thrust by turning the rotor out of the wind.

So this calculation demonstrates clearly why developing of a big Savonius rotor for the generation of electricity is a very bad idea.

[leviatan]

Adrian you are a old man, with a large experience. ¿You cant understand exist places where a hawt are imposible to use? I cant install a hawt here in my home, first for regulations, second for distrubing sounds, third for negative visual impact, fourth i am sourronded by trees and any kind of obstacles ( constructions, and differences in the level of the terrain). That means the wind direction and speed change continuosly.
The average wind spedd in my zone is 18k/h that is  the minimal to worth any wind of turbine.
Probably the most of the hawts cant got so much current with that average wind speed and more if the direction and speed are changing all the time, forget to got a laminar flow wind here.

Then i guess initialy the bad idea is to invest in a wind turbine here in my location, but the worst idea would be to produce  a hawt that will give zero in this conditions and the life of the equipment will be so short.

Then because the wind will be turbulent and slow almost all the time, i choose a wind turbine model that can work and take something of a slow and turbulent wind.
Like you said a hawt take may be 20 times less of material for the same power, then is more expensive to do a vawt savonius.
But the savonius will work ( with low efficience but  will work) and can resist the turbulent wind conditions by years.
At change any other kinds of vawts or hawts cant resist turbulent winds by a long period without premature failures.
Then the bad idea is to produce a wind turbine for my location, the worst idea would be to made a hawt ( and is more cheap to buy thems).

The savonius will be a expensive and low efficience machine but will work, and will be fun to see she spining.
The other considerations about efficience dont have space one time the location not is adecuate for other vawts or hawts.

 

[Adriaan Kragten]

Strong variations of the wind speed and the wind direction have a negative influence on the output of a HAWT. However, you should not believe that these variations have no negative influence on the output of a Savonius rotor because a Savonius rotor accepts wind from any direction. Savonius rotors also perform best in steady strong winds. A small HAWT like the VIRYA-2.02 will follow variations of the wind direction rather fast and so it won't suffer much from variations of the wind direction. If there is too much turbulence at low heights for a HAWT, you have to use a higher tower. What you spend extra for a high tower for a HAWT is only a small fraction of what you spend for a Savonius rotor which generates the same power at the same wind speed.

If you take the invested money in your Savonius rotor and if you take the value of the generated electric energy, you will never generated enough energy to pay back your investment during the whole lifetime of the windmill. If you take the energy which was needed for all components, the windmill will never generate this energy during its whole lifetime. So it is a waste of resources especially because you are using scarce materials like neodymium and copper in the generator. But this is not only the case for Savonius rotors. It also counts for many small HAWT's if they are placed at sites with too low wind speeds. So what you are making is not an efficient wind turbine but only a piece of art. If looking at a rotating piece of art gives you enough satisfaction for all your efforts, go on and enjoy your work.

[MattM]

If you add sufficient weight to your project it will help level out fluctuations AND can be used to decrease wear and tear under too low of winds.  Even better if you can brake it under extremes of highs and lows.  Most of these projects are multiples of the cost of grid tie, so don't let that bother you.  The utility by definition will always beat you in price.  But not every location has utilities.  The bulk of the projects here are not about price.

[DamonHD]

Setting the price to one side, a project may be about cutting carbon, and that is different, but also hard to do.

I'm fairly sure that my off-grid stuff has not cut carbon of itself, but has helped me think about other projects that have.

Rgds

Damon

[bigrockcandymountain]

If you do build this large savonius, please add a brake disc for stopping it in high winds.  A mass that large, even at 200rpm is a terrifying thing to be anywhere near.  You really need some safety systems, especially since it sounds like it will be near houses and people.

The cost of this project is going to be very high.  A 150mm id bearing of decent quality is not a cheap thing. Neither are any of the other materials. 

I know the goal of this project is not anything practical, but the joy of watching it spin will quickly wear off if it isn't of some practical value. 

[Bruce S]

leviatan:
It took me a little while to find what I think might be helpful of your question back in your first few posts asking of previous builds.
A long time member (GoVertical) posted a very well detailed account of his build. It should be of interest to you.

https://www.fieldlines.com/index.php/topic,143852.0.html

I personally am interested in pics of your magnet layout and how they get on with the Aluminum "E".

Cheers
Bruce S

[leviatan]

leviatan:
It took me a little while to find what I think might be helpful of your question back in your first few posts asking of previous builds.
A long time member (GoVertical) posted a very well detailed account of his build. It should be of interest to you.

https://www.fieldlines.com/index.php/topic,143852.0.html

I personally am interested in pics of your magnet layout and how they get on with the Aluminum "E".

Cheers
Bruce S

thanks for the aport bruce. i will give a close look to the problems of construction of this other guy.
About the E probably i will do some of theys with plywood to let understnd the concept on images, because the companys in china are since 20 days in new year holidays and all my advances are stoped until theys will back to the work again.  When some things dont depends only in my self is very much complicated the whole subject to advance.
Other complication related to chinese companys, are they have splited his industrys in different regions of the country.
The heavy industry where to got the steel tubes is on the north, the place to machine the parts are most commoun and i can got companys in shenzhen ( the south of china) for the magnets i can got in both extremes, north and south, for the aluminum i can got easily commoun profiels in the south, but i not have clear the production companys also are in the south for that item ( custom profiles), to produce the profiles at request.
 Some times and depending of the honesty of the sellers, the shipping cost from the north to the south can cost the half of the goods value if are heavy weight goods. Then all is a continuous willing to got the real price for the goods and for a accurate shipping cost.
 But i am on the way, i already spent usd 3000 in some parts, then now not exist comeback .

About the mass of the turbine spining at high rpms, will be contained weight, around only 120-130 kg, and at higher diammeter the rpms are slowers, a lot. Do you can see videos of any kind of commercial and no commercial savonius, and when theys got a diammeter  equal or upper than 1.50 meters the rpms are barely a worry.

 Answering to bigrockcandymountain: About the quality of the bearings, yes exist huges diferences in costs for the same kind of bearings, but also the rpms  at that lower range (and having in account the bearings are measured his lasting life in millions of spins) cant got a premature wear of that parts like could happen in a normal motor when the millions of spins can be obtained in a year of useage.

All confusions about weackness of the rotor are taking like base the videos of litlle prototypes where the RPM are very much highers. Take a look to the luvside turbines videos and you will take a idea of the rpm of a big savonius when you increase the size to semething useable.

Any way that subject of a brake disc of commoun motorbikes could be a solution for that subject in a extreme wind, but is a "simple" subject to solve by that not were mentioned earlier, because not is complicated to add that system to the turbine. Here the most complicated and expensive is to produce a axial PMG that works at deliver some current at that lowers rpms without a gearbox.
That is the big question where i am doing my first aproachs, to solve the issues related  at one  PMG with that features.

I have 100% confidence in the design of the turbine ( in fact is simply). I cant to say the same about the PMG, i dont know if the size of the coils, and quantitys of stators discs will be enough, or a excess.... today i will do the second coil, i do yesterday one of 15mm tick with 0.7mm wire and took 663 rounds of wire, and was exesive in all aspects  (inclusive using 1.2mm wire tick, would continue having a extreme quantity of rounds) .

Today i will do one of only 10mm height to simulate the current in a stator with two layers of coils of 5mm each one. Some things until you dont have on hands and do some tests cant calculate if are enough or a excess.

[Adriaan Kragten]

If you know the final geometry of your Savonius rotor with three blades, you should first make a scale model scale 1 : 5. This scale model won't be very expensive because the mass is a factor 125 lower than that of the original. The scale model is then placed on top of a truck and if you drive the truck at a day with no wind, you can measure the wind speed rather accurately. If the rotor turns unloaded, you can easily calculate the unloaded tip speed ratio lambda unl. if you measure the rotational speed n. If you find an unloaded tip speed ratio which is much lower than 1.8, you know that using three blades was the wrong choice.

As the right part of the Cq-lambda curve is about a straight line for a Savonius rotor, the optimum tip speed ratio lambda opt. is about half lambda unl. Next you should load the shaft such that the rotor runs at this optimum tip speed ratio and measure the torque. You can use the friction brake invented by Prony. This might be rather difficult on a truck but this is the way how to measure mechanical power. Then you can calculate the optimum torque coefficient Cqopt. The maximum power coefficient is then found as Cpmax = Cqopt * lambda opt. I expecty that you will find a value of Cpmax which is lower than 0.15 for a Savonius rotor with three blades. If you are happy with that, build your final rotor. If you are not happy with that, you have only wasted the costs of a scale model and some measuring equipment.

Another point of the Cq-lambda curve which can be measured rather easily is the starting torque coefficient Cqstart which you find if you measure the torque if the rotational speed is zero. If the Cq-lambda curve would be a straight line in between lambda = 0 and lambda unl., you could draw this line if you know only two points. But measurements on real Savonius rotors show that the Cq-lambda curve is only about a straight line in between about lambda = 0.5 and lambda = 1.8 and that Cqstart is lower than the peak value at lambda = 0.5.

[leviatan]

Today I did the first test of a coil on the lathe. I really don't know if what the current produced is correct or if it should produce more.
The coil I made is with 0.7mm wire (the only one within my reach at the moment). And since it was only for testing I didn't want to make 2 coils of 5mm thickness, instead of 1 single one of 10mm thickness and simplify the test (I don't think the improvement between using two layers of thinner coils in the stator would have a dramatic change later, but in any case it could only get better).

the coil of 10mm thick, and 25mm wide, reached 400 turns of 0.7 wire. If I use 1.2mm wire then I think it will take a third of turns, but the test was done with this 0.7 and 400 turns.

I used a charge regulator/rectifier instead of a basic bridge rectifier, because I didn't find one that I know is somewhere in the shop and I don't know where currently.
I don't know if the use of this type of rectifier consumes a little more current than a basic bridge, so I have doubts about the measurements that the tester gave me.

Well the important thing: at 84 rpms with an imaginary disk of 35 cm in diameter (because my imaginary disk had only 2 poles instead of the 16 that a complete rotor should have) the voltage went up and down from 0.35 volts to 0.85 volts regularly ( imagine that the problem may be the charge regulator that consumes a little more current than a basic rectifier,  or that the rotor should rotate faster to compensate for the lack of poles in the circuit and give a more continuous current without pulses so spaced).

The question is how to know if this measurement is correct (I don't understand why it makes these regular fluctuations) and if you use a complete rotor with 16 poles, how much should this measurement rise? Should I multiply by 8 directly? Or is the sum of voltage not linear as poles are added?

For bruce: you can  see in the images, the position of the magnets in the wood and the coil inside, then you imagine the same but instaled in 16 pieces of E of aluminum,  to form the complete circle of the rotor. Probably  you can understand well the design with only that photo, but i dont know manage 3d programs to do a draw in 3D to help  visualize.



PD: the projected rotor will be 50cm in diameter, the wood in the lathe only reaches 35cm, which is the maximum that enters the rotation of my lathe, this affects the cutting speed of the coils but since I use 84 rpm instead of 60rpm it could compensate the difference i guess.

[MagnetJuice]

The voltage that you need to measure from the coil is the AVERAGE AC voltage. Connect the coil straight to the meter. Without the RECTIFIER. That measurement will be the AVERAGE AC voltage for that one coil.

To convert that voltage to DC you need to convert it to PEAK AC voltage.

PEAK AC depends on the number of phases that your alternator will have.

Here is an example:

If you measure 1 volt from the coil and you have 3-phases, you multiply by the square root of 3 (1.73) to get the total AVERAGE voltage.

1 x 1.73 = 1.73. So your AVERAGE voltage for one coil for the 3 phases is 1.73 volts.

Now you need to covert that AVERAGE voltage to PEAK voltage. To do that you multiply the AVERAGE voltage by the square root of 2 (1.41)

So your DC voltage will be 1.73 x 1.41 = 2.44

However, there are more things to consider.

A large alternator that is wired in STAR, has many coils in series, so you multiply the voltage from that single coil by the number of coils in one phase.

Example:

If there are 6 coils in one phase, you multiply the 1 volt from your coil by 6.

1 volt multiplied by 6 (coils) = 6 volts, multiplied by 1.73 = 10.38 volts, multiplied by 1.41 = 14.63 volts. That is you total PEAK AC voltage.

Now you can use a rectifier to convert that PEAK AC voltage to DC voltage.

You will lose about 1.4 volts in the rectifier. Subtract that from the 14.63 and your final DC voltage will be 13.23 volts.

That is almost enough to charge a 12-volt battery. To charge the 12-volt battery, you need at least 14.8 DC volts.

I hope this is clear enough.

Ed

[Adriaan Kragten]

Rectification is explained for a different number of phases and for star and delta in my public report KD 340. Here you find the derivation of the formulas with which the AC voltage of one phase can be transformed into the DC voltage after rectification. If the voltage is low, you also have to consider the voltage drop over the rectifier diodes.