A Consideration of Wind Turbine Dynamics – by John Curtis

Posted on 25/02/2012 by

About Dougal Quixote

Slightly mad. Always believes a cup is half full so continues to tilt at Wind Turbines and the politicians that seem to believe it is their god given right to ruin Scotland for a pot of fool's gold.
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7 Responses to A Consideration of Wind Turbine Dynamics – by John Curtis

  1. Ann Cowan says:
    25/02/2012 at 6:57 pm

    Only if they worked better! That was 8 years ago. We have got now thousands of horrid wind turbines but have not got rid of ANY coal-fired power stations.

    Reply
  2. Dougal Quixote says:
    25/02/2012 at 7:43 pm

    The efficiency of Wind turbine blades are always going to be limited by the air flow over them. Every sailor knows that wind is not constant, even at sea. Any inland sailor knows that wind eddies, grows in strength and weakens. All within moments. That is the nature of the beast. Wind is simply air mass moving from areas of high pressure to areas of lower pressure. The steeper the gradient, the higher the wind and the greater the volativity. And that is referring to the isobars not the topography. Wind is also not directionally constant either. The effect on turbines then is manifestly affected by the topography. In one direction you may get a relatively smooth flow up a valley, back 90 degrees and you get a tumbling vortex over a hill. Analysts create wind maps from their meteorological masts to ascertain the most prevalent directions and then place the turbines to take advantage of that. However this is limited by the variability of weather patterns. Weather can change one year to the next and what was good for one years series of events may not be optimum for another. It is of note that wind tends to drop in the early evening. Just that time when everyone gets home, turns the televion, the lights, the kettle and the cooker on and in the brave new world plugs in the electric car. This is particularly true of coastal areas where the bulk of the turbines are situated, Turbine blades are designed to operate at the optimum windspeed for an area, but therein a conflict is caused. Winds outside that umbrella result in lower than optimum performance or no performance at all. A blade may be turning but if the wind has insufficient energy in it, or too much, the turbine will be operating at only a fraction of its capacity, and often at little more than enough to sustain its own operation. Mechanical limitations also have a limiting factor on the blades and too much wind or highly volatile(gusty) wind will normally necessitate an automatic shutdown. In reality wind has no use in a modern industrialised society because the cost of backing up that variabilty and intermittency is simply not economically viable,

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  3. dave ward says:
    26/02/2012 at 9:55 pm

    There seems to be a misunderstanding in the second page of that article. Turbine blades normally operate upwind of the mast, NOT downwind as he implies. They won’t be passing through the highly turbulent air shown in figure 2. There will, however, still be interference between the tip vortices and the mast which will undoubtedly give rise to vibration (probably the “Thump” sound which is causes so many complaints).

    “This is particularly true of coastal areas where the bulk of the turbines are situated” – And the “Sea Breeze” effect often leads to a zone of highly variable winds where the prevailing Westerlies from the land meet the Easterlies from the sea (at least in the South East of the UK). You can also get “Inversions” which give completely different wind speeds & direction under such conditions – particularly in the 200-600ft height range above ground – just the area those blades are sweeping!

    As a (now former) microlight pilot, I am fully aware of the conditions that turbines operate in. I am also particularly aware of the turbulence downwind of any large structure and even big trees! This aspect is frequently overlooked in the siting of many smaller units, and I can tell, just by looking at the surroundings, how ineffective some of these are going to be.

    “It is of note that wind tends to drop in the early evening.” – Just the time people such as myself and particularly balloon pilots get airborne!

    Reply
    • Dougal Quixote says:
      27/02/2012 at 12:13 am

      John is open to correction. I will forward yours comments.

      Reply
    • Dougal Quixote says:
      29/02/2012 at 1:31 pm

      John’s answer was unprintable but he offers his apologies and blames it on advancing years and the inapproriate application of Ardberg. Mind you he did say that at least it proved someone has read it which was very gratifying. No one in Government seems to be listening to anyone except themselves these days.

      Reply
  4. dave ward says:
    29/02/2012 at 3:20 pm

    Thanks for the update – apology accepted! It also occurs to me that another source of noise could be from the tip vortices reflecting off the ground as the lowest blade passes. I’m thinking of parallels with the Cessna 336-337 light aircraft, which have a rear mounted “pusher” engine and twin booms supporting the tailplane. These are notoriously noisy, due to the proximity of the booms to the prop tips.
    http://www.337skymaster.org/images/jerry337S.jpg

    Reply
    • Dougal Quixote says:
      29/02/2012 at 3:47 pm

      Flown one and they are horrendously noisy. Especially if you get the blades out of sync. Which is where the main problem noise wise lays. Somehow it is always more difficult to get the blades balanced with a push me pull me configuration than a straight twin. Either that or I was just a hopeless pilot. Now I leave that to No1 Son.

      Reply

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