A few of the many lower rated wind turbines on the Tehachapi ridges, which are also appropriate for installation near loads on a singly distributed basis for net billing power generation, are shown on the left and on the right. Turbines with a 108 kw rating are on the left. A similar turbine of 65 kw plus rating with upgraded blades providing a 25% increase in average power production is shown on the right. Hundreds of similar turbines that dot the hills here in Tehachapi, CA are providing electrical power at contracted rates to the power utilities in California. Click here or on either image to download a compressed folder including drawings, images, and a .pdf file of actual past meter readings taken of sample units in the wind projects, with weekly cash revenues calculated of their profit-making abilities.....
The question of where does high level academia and the national energy labs stand on the issues can be given a look. Wind energy falls into the category of being somewhat rudimentary in technological sophistication. Added to this is the long turnaround time of experimentation. A gulf can be said to exist between the few pure science theoreticians still to be heard from and the more practical developers and manufacturers bent on minding safety and reliability issues. No one quite understands the intricacies of how the computer software is being written and updated and it is the computer that has a pre-emptive voice over everything. To say, even so, that wind turbines follow the path of least resistance and do so "by guess and by gosh" is not far from the mark. The business of energy, meanwhile, is a hard driving business. Air does have its largely unrealized great mass weight in even modest dimension volumes easily comparable to the great displacement weights of large ships and the continuing, overwhelming tonnage of coal burned every day. The turbines, though, come down to seeming to be a little afraid of making use of the motion of air as wind in the process of delivering wind energy.
Adding blade length has been given preference as an easy path to gaining performance, the "blade swept areas" being proportional to the blade lengths squared. When the energy derived from only one inch of blade length thereby provided comes to nearly one kilowatt as is now expected, an end to this exceptional gain may find itself happening, as even realized intuitively. Something other than blade length may be necessary to extract further advantages beyond simple linear energy increases if the number of blades is to remain at three.
A European wind turbine manufacturer now is developing an 8 MW turbine with 80 meter long blades as seen above on the left. To look at the prototype one would have to say it looks mighty attractive. But if those very long blades are to do much at all in extracting energy from the wind passing through the very large areas between them something more may need to be done. A return to small scale experimentation could be initiated to find new paths to follow. Something along the lines of the No Drag Flaps described below tried in limited tests here in Tehachapi, California could be given some thought.
The small wind turbine blade testing that happened here in Tehachapi, California under IntegEner-W auspices covered a period of several years. It was documented with numerous images, a few of which are copied into this story, brief as it is, written in summary form. It was a worthwhile effort because it provided real answers to unanswered questions. The wind is free but just making wind turbines larger is not the only answer to increasing energy production. Nor are studies of published software correlations from practice based on data fed back from operating turbines an answer to how to reinvent blade profiles. In aviation, efforts are well known directed at reviewing wing enhancements, not just profile adjustments but also such features as winglets, ailerons, slats, and flaps. It is not surprising that wind energy would find unanticipated interest in doing so as well in the name of better performance at lower costs. But a solid foundation of theory must be agreed upon beforehand. The theory which underlies our work is based with great care on Newton's Laws of Motion applied to fluid flow primarily undergoing changes of direction in the blade frame of reference. Thus it has been given the name "Air Mass Flow Deflection Theory". Click here or on the image above to download the story in Word format at .25 MB.
News Report Formed metal alloy flaps 7.5 feet long and 6 inches wide are available for use in doing this mod. It is estimated that a 25% gain in the average rate of power production over time would result with this blade mod on 50 to 100 kw rated turbines. The No-Drag Flaps act to as much as double and triple effective blade widths - and their power - without physically doing so. Proven in smaller scale testing. Under the protection of an IP attorney.
Even larger blades with an ordinary Clark Y-type of airfoil profile can see improvements, it has become a certainty, with the relatively easy addition of a second element, similar to the cases seen elsewhere herein in small scale experiments. What is shown here is called the "No-Drag Flap". It was under the aerodynamics "deflection theory" that this hypothesis and follow-on was made. As indicated by clicking on the image to the left, benefits include better blade performance in light winds and at the blade tip under high tip speeds, both recognized as cases of high TSRs (tangential speed ratios). In effect, the blade no-drag flap, at these conditions, substitutes for increasing the blade chord when increasing the blade chord materially adds unwanted rotor "solidity", that is, percentage of blade area to rotor area. Wind turbine blades do better without extra wide chords in controlling stresses during overly strong winds.
The high TSR case remains an interesting study. Consider that the wing lift force for aircraft is at right angles to the incident airflow while the blade driving force for wind turbines may be directed much closer towards the incident airflow, even as little as just 10 degrees or less off of it. The use of such a device as the trailing edge no-drag flap may only be the start of technology intended to better satisfy the demanding aerodynamic and structural requirements imposed.
Aviation jetliners now may have something similar. The cover of the March/April 2014 issue of "Reinforced Plastics" magazine showed such a jetliner taking off with some sort of wing trailing edge flaps deployed. It would make sense if it is. The additional lift provided without an increase in the wing angle of attack (greater lift-to-drag ratio) would be quite welcome.
A similarity also is found with the airfoil "wing" now seen on trunk lids of some cars as seen on the right in a pic from Wikipedia. These were designed initially for high speed race cars from stories told on the Internet. Various advantages claimed included a reduction of drag due to the lower Reynolds Number. This is to forestall questions of whether the "no drag" quality claimed for the flap is in fact supportable.
High TSR Research and Blade Kilowatts Per Meter While the blade length required for each kilowatt of turbine rating can be one meter or more for the three blades of small turbines, the multimegawatts do much better, capable of producing as much as 20 kilowatts on average per meter of blade length at rated conditions - considering the total length of all three blades (an interesting do-it-yourself calculation). This is not all. The power production at the blade tips is greater by as much as twice this average, thus can be, at least presumably, 40 kilowatts per meter at the blade tips. Since total blade length considered linearly becomes a basic input variable for increasing large turbine ratings, these values become something of a standard multiplying factor to be recognized when scaling up turbine ratings. Identifying what is at stake here is important. The need to pursue higher ratings to reduce the cost of windpower and the number of turbines required for wind turbine projects being planned is not to be dismissed lightly. Here with the "No-Drag Flap" is an approach that can beneficially and effectively reduce the blade aspect ratios without actually reducing the blade aspect ratios, thus making possible a higher blade kilowatts per meter performance. This is a new research direction to take. Further, introducing the measurement of blade "kilowatts per meter" is accordingly how progress can be gauged.
For This Blade Mod
These are stories contributed by others.
During operation at ground level and at somewhat greater heights in winds measured with a hand held Kestrel wind meter of some 20 - 22 mph, it routinely runs at rotation speeds of 1000 rpms into 400 watt loads - eight 50 watt car headlights strung in two parallel rows of four each. This is a blur speed with blade tips moving at 175 mph not unlike the tip speeds of the large megawatt rated utility wind turbines. This is somewhat like what we have seen before in lesser dimensions (look in the left hand margin for the "Power Gap Blades" image).
This concept has worked well for us perhaps due to its similarity to the use of leading edge slats for the high lift case of aircraft wing profiles. (See Abbott and von Doenhoff Section 8.6 on page 225 et seq. of the 1959 edition.) More to follow as updates are posted. A limited number of these blades, as modified, are available for purchase on the Home Projects page.