 Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me. |
Forum Index : Windmills : TSR’s for Aluminium/PVC blades
| Author | Message | ||||
KarlJ Guru  Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
you can change the TSR's by changing the Angle of Attack (AOA) a couple of degrees either side of the 10 degrees recommended. TSR performance So the great question now is, how does this affect the power able to be extracted and cutin windspeeds If we shoot for a lower AOA the TSR is higher, which appears all good as the rpm gets up to F&P power producing level faster so where is the down-side? It appears to me that the 3.0m diameter dual F&P machine is the ducks guts as far as F&P things go with a massive diameter in terms of capture area for an F&P(even2) So capture area is 7.01m2 and max rpm should be limited to 550-600 (by furling not blade angle) in the interests of not going into runaway from F&P iron core design. Thus assuming a cap doubler arrangement is it possible to calculate the ideal TSR. ie optimise it by lowering of AOA to make it spin up quicker, cap doubler to stop it stalling, enabling the higher outputs obtainable with delta wiring of the stators without the drawbacks of no power 90% of the time. I hope to find that we are in fact now at the cutting edge of F&P performance, great blades (PVC and Aluminium extrusions) , great electronics (cap doublers), and best yet a hobby mill that produces enough power to warrant grid feed, without costing $20K plus. Thus the Phill M dual looks like a pretty impressive beast for the money next to this Expensive turbine which only has 2.1m diameter and thus will be far far shorter in the available wind to catch with less than half the wind capture area. in fact based on their numbers of 100KW/hr/month at 5.2m/s average windspeed site, (which I have) double the capture area = double the output right? Thus theoretically capable of 200KW/hr /month on that same site for 4 times less investment. thus return would be upto 8 times better... Luck favours the well prepared |
||||
Perry Senior Member  Joined: 19/11/2009 Location: Posts: 190 |
Hi Karl, Interesting question. Wouldn't lowering the angle of attach impede the ability to get to high speed quickly? Perry |
||||
| Dinges Senior Member Joined: 04/01/2008 Location: AlbaniaPosts: 510 |
[quote]If we shoot for a lower AOA the TSR is higher, which appears all good as the rpm gets up to F&P power producing level faster so where is the down-side? [/quote] I expect the downside is less torque, if we assume for a moment that AOA doesn't influence total power harvest capability: P=M*v (power = torque * velocity) If decreasing AOA increases RPM (i.e. velocity) then, given constant power, torque must decrease. It's the price you pay for higher velocity; like gearing, RPM/speed comes at the price of torque, and vice versa. But it may well be that decreasing (or otherwise optimizing) AOA actually increases total power. Anyway, there should be an optimum AOA beyond which power will decrease, no matter if you increase or decrease AOA, because of L/D ratio: There is one optimum L/D ratio, where for a given amount of drag the lift is maximum. Changing AOA puts you in another spot on the L/D-curve, where you get more drag (=power loss) for a given amount of lift (lift translates directly into power to the shaft). The above is just what I recall from some glider aircraft aerodynamics classes over a decade ago. And the topic never interested me much anyway.... Sparweb could probably answer you much better. PS: see this file for some more explanation: http://www.mjw.co.at/downloads/Airfoils_and_planks.pdf , on page 5 and 6; page 5 has the Cl/Cd graph of an airfoil, whereas on page 6 you see Cl/Cd as a function of alpha (AOA). Notice how sensitive it is w.r.t. changes in alpha.... suggesting that there may be a reason to try to optimize alpha in windturbines too, for maximum power harvest? Peter. |
||||
| KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
I'm thinking not necessarily for max torque but max rpm, as long as enough torque is there to turn the generator (not that much I think -but Phill has done testing with the arm in a lathe to prove out the theory) Pete, i'm right up to speed with A/C aerodaynamics, I used to teach the stuff when I was a flying instructor but to me a windmill is arse about hence I still havent entirely got my head around it. Similarly Perry I dont know, the blade will have less torque but everyone says these are torquey blades thus to sacrifice a little for some more rpm seems like a good idea. I think the cap mod will allow them to spin up easily as if there was less load so shouldnt face a stall scenario and then not accellerate. Traditionally for larger aircraft the ideal AoA is 4-5degrees to maintain laminar airflow and keep drag down. Luck favours the well prepared |
||||
fillm Guru Joined: 10/02/2007 Location: AustraliaPosts: 730 |
I run my AOA at 8deg , with this airfoil I have found this gives high RPM and high torque , under that I noticed a drop in start up torque and the ability to keep running in wind under 5klm on the F&P . The set which are on the F&P dual are 3.150 Dia and have been clocked at 780 rpm outputing 750w , but after the failure of the 3.2mt set on the Ax Fx which had reached 2.8Kw @ 500 rpm , I put the 3.15 set on to the Ax Fx and I then recorded 3.2Kw @ 550 rpm in 50Klm+ , as Oztules sumed it up " this is the type of thing that baffles engineers " Expecting lower output by decreasing Dia is not always the case in good wind , but would impact in low wind . Now that the pvc set are back on the F&P Dual I have been giving thought to docking 50mm a time of the Dia to try to find where the sweet spot is in size is right for low wind start up and to allow them to get up to 100~150 rpm in 10+ Klm , as I run one stator in star & one in delta to give a stagered cut in 7x2p 80s the actual cut in without the cap/doubler would be 200 & 300 . It works extreemly well , as I am in a low wind area and most days with wind between 10 ~ 18 klm there is almost nothing between the Ax & F&P. The torque and speed are both achievable with this blade profile , and matching Dia and AOA is a trial and error process for the average wind you have . PhillM ...Oz Wind Engineering..Wind Turbine Kits 500W - 5000W ~ F&P Dual Kits ~ GOE222Blades- Voltage Control Parts ------- Tower kits |
||||
| KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178 |
There you have it, 8 degrees is the lowest recommended AOA hence the highest TSR, and here I was thinking I would be breaking some new ground going there. Thanks for doing that R&D too... Is there anything you haven't covered Phill? have you run the 100S unmodified in star and delta on the mill? I know you went there in the cap testing and you said they were pretty close. I only ask because I basically have an abundance of stators, polished up a set of 80s as recommended, rewired one for 2X7C Star and 2X7C Delta did the whole , decogging, smoothing off the high spots created by decogging, sealing with varnish, hub-primed with plastic primer, painted in a nice gloss purple (even picked out a brown one to start with as suggested!) I'm keen to try the pair of 100S though as they really do look the goods with the heavy wire, and sacrificing a little of the low end to get some more out at the top makes sense for me as I have no AX-FX....yet, going to need to move (sell) one helluva lot more F&P's to get there. Luck favours the well prepared |
||||
 Print this page |
 |
The Back Shed's forum code is written, and hosted, in Australia. | © JAQ Software 2025 |
