No. the turbulent disturbance in front of a car, like that in front of a wind mill, is roughly than same scale size as the object causing it. In the cars case the bird had less than 22 feet of turbulence in front of the car moving at the bird at 88 feet per second (60mph) so no more than 0.25 seconds for the bird to take evasive action. In the case of a large commercial power generating wind mill, the bird notices the turbulence at least 200 hundred feet in front of the machine and has at least 40 times more time to avoid flying into the relatively slowly turning blades. That is why it is extremely rare for a commercial wind mill to kill a bird - much less than one per year.
Wind turbines do not project useful avoidance information in turbulence hundreds of feet upwind, even, let alone at angles, detectable by birds; and the blades are moving well over one hundred miles per hour in normal circumstances (at least 5X wind speed, by design). They are minor killers of birds, but that could change if tall ones were built across night migration funnels or some such especially bad area. Commercial windmills kill a few hundred thousand birds every year, probably more per unit than cars kill but much less total. The savings in bird threat from this funnel setup is probably nil - it's advantages, if any, would be in areas and situations full of birds and not as useful for blade mills anyway, so the net threat might easily be greater, not lesser.
You guys are both wrong. The "turbulence" caused by the wind turbine's motion is detectable from a much, much longer distance than 200 feet; perhaps 10x more. This disturbance is called sound. For a car, we don't notice it because the sound of the engine is louder.
Yes they do, but it is not normally called "turbulence." I used your term, but now must clarify. Birds know what the speed of the air the are flying thru is and notice very small changes in it - that is what I was saying - the wind begins to slow several turbine diameter up stream. Technically this is large scale turbulence, but few would call it that. Yes the tips may be going that fast but the air spill around would carry the bird away from the being hit by the tips, even if the bird did not actively avoid it. This air spill effect helps birds, not to heavy (lot of inertia), not get hit by cars too. (Cars do kill pigeons, but not sparrows.) I am not sure how much the wind mill noise helps the bird avoid being hit by the wind machine. That would depend on how accustomed bird is to hearing it. It might help a lot if the bird has learned to correlate that noise with danger.
?? What is this effect called? I have never heard of an effect that, on average, moves birds/debris away from wings. It would be nice if such an effect did exist tho.
I don't know if it has a name. I called it spill over or spill around effect. You can understand that it is real by assuming it is not. I.e. Assume the wind passing thru the "swept circle" has been slowed down from 30 mph to 20 mph. I.e. the KE in the wind machine captured is 1 - 4/9 of the total in the wind.* If there is no "spillover effect" the air moving undisturbed just out side of the swept area is still going 30 mph - that would be infinite shear - stream of air at 30mph in contact with stream of air at 20 mph. BTW, I bet you have seen it. I. e. have you never seen a bumble bee look like it is to meet certain death against the wind shield of your car, be saved by the "spill over" effect? I.e. not go "splat on the glass"; but be survive by being swept out of that over the car. * BTW, that is not far from optimum power production. Slow the wind down much more and you do get more energy out of each Kg passing thru the swept areas but fewer Kg do that each minute. Slow it down much less and then many more Kg of air pass thru the swept area, but you collect too little KE from each Kg.
I don't think it has a name (it isn't vortex shedding). It's just reflective of the fact that airflow doesn't just crash into objects, it flows around them. Any object flying in that air will follow the curved path of the air to some extent -- but the heavier the object, the more it will deviate from that path. Please Register or Log in to view the hidden image! A parcel of air on one of those streamlines stays on the streamlines. A balloon, for example, will simply get out of the way of a passing car. Heavier objects are still deflected, by an amount depending on their weight and aerodynamics.
Birds hit tall stationary buildings and structures, when flying downwind especially. They get hit by the wings of even slow, small planes taking off. They get hit by cars. Even if they are flying directly downwind they don't get enough info from the small turbulence changes (and essentially none from the sound - birds don't hear well, flying their ears are in a noisy slipstream already, sound does not travel well upwind, and the information from it is vague). The mere slowing of the air is a very small barometric pressure difference only, almost impossible to "feel" (remember the bird is flying through the air, which is otherwise still relative to the bird - the bird's relative air speed does not change due to the speed of the air itself, which is always changing relative to the ground anyway), and gives no information without a visual cue. This is fantasy. Those blades cut through the air at high speed and without creating much of a front wave at all - they are lethal, and avoidable in their sweep area only by luck or visual reflex. Cars do kill occasional sparrows, despite their superior acceleration and maneuverability, quicker flock warning reaction, and less sedentary feeding behaviors. Small, light roadside feeding birds that lack the city flock behavioral advantages get hit proportionately often - goldfinches and juncos and the like. Birds in traveling flight are not dust motes or insects wafted about by every current of air - they are ballistic, and they miss solid objects in their path (that block the wind completely, much more upwind warning than a windmill that merely slows it) by seeing and avoiding them, not by some kind of aerial cat whisker effect. Birds in migration flight at night, or panicked, or otherwise incapacitated in visual navigation (skythrown electrical lighting is notorious for disorienting birds), will slam into even stationary buildings and communication towers and other high structures. That's straight downwind or upwind - from any side angle of course none of this is even in discussion. Again, wind turbines are minor killers of birds in general (a few hundred thousand a year in the US) - but mostly because so far they aren't installed in especially bad places at bad heights. This funnel design, if it has any advantages at all, seems likely to have them in generally worse locations and heights for bird hazard - so any claim of superior bird safety is dubious, is all. Minor issue.
Almost always as they try to fly thru bird perceived holes in the building, which we call windows. I agree they don't perceive the wind slowing down by directly feeling it to do so or by noting a slight change in the air pressure. They perceive their motion speed visually with the near by speed of the ground receding behind them, Exactly like you visually perceive the speed of a train looking out the window even though you, like the bird, don't directly feel the speed. This only reflects you lack of understanding that the flow thru the entire swept area is slowed - it is not the direct / near by effect of air flow over the blade, which is much like the over an air plane wing locally. It is not "full stagnation" of the air against the swept circle, but the slowing on axis begins more than a diameter up stream. A large stationary circular screen of area equal to that swept by the wind machine blades that slowed the air flowing thru it the same amount as the wind machine does would also slow the wind down more than a diameter ahead of it too.
The only two videos of a bird being struck by a wind turbine blade did NOT involve the blade impacting the bird but the bird being sucked into impact from the side. The low pressure surface draws the bird into the blade. Truly, wind power sucks!
Do you have a link to these videos? I'd like to see that for myself as find it hard to believe. I think that up stream there is only pressure increase, and it is behind the windmill that there is pressure reduction.
That makes no sense: you are describing a fan, not a turbine. On the low pressure side the air is still moving away from the turbine!
1) During the day, especially during short distance or avoidance flight, that is common. During night migration and traveling flight, other factors become more important. 2) Wind turbines offer large holes to be "perceived" and flown through - they are mostly hole, in fact, unlike windows where the hole is a visual illusion of some (various) kind - and their blades move faster and differently than birds are prepared to handle. 1) Again, this is different at night. Many night-migratory birds avoid ground obstacles (including those that, like towers and such that birds also hit, not just slow but completely block the wind) by flying at heights where such things are not expected to be. 2) The wind changes speed constantly, for many reasons - nothing in the natural world slows the wind the way a turbine does at such heights, and as far as anyone knows no bird is capable of comprehending (let alone making an appropriate split second and dramatic response to) the structure and properties of an invisible turbine a hundred meters away and fifty meters blade span across its path (counting left and right location possibilities, 100 meters of hazard) approaching at 25 m/s, merely by noticing that the wind is slowing. 3) The slowing of the wind increases the flight residence time in the sweep area, and any turbulence confuses the bird's reactions - that increases the hazard, not decreases 4) None of this even applies unless the bird is traveling directly down wind, an unlikely circumstance in migratory or traveling flight. I know of no data regarding the most hazardous approach angle (will vary by species, weather, time of day or year, etc), but notice that the reduction in cross section area of a single turbine is partly countered by the typical layout of large turbine fields as well as the increased sweep area residence time - migrating and traveling birds are often moving in fairly straight lines. Please. Nothing I have posted indicates any failure to comprehend the situation. You haven't thought it through. Like this: So a bird flying across the wind behind the turbine might easily be deflected into the sweep area from the downwind side, much as a motorcycle is deflected toward a large truck or a solid barrier briefly passing upwind. The main reason the 50,000 or so of the larger size wind turbines in the US only kill a few hundred thousand birds every year - many fewer total, although more per unit, than windows or cats or cars - is their typical (so far) location and spacing and positioning away from where birds do most of their vulnerable flying. Birds that do fly where turbines spin get hit quite often. This safety feature may not be shared by a funnel design (if its advantages are anything like the claims) and so its claimed advantages in bird safety are questionable at best - that was my only relevant point, OK?
Please Register or Log in to view the hidden image! Note by worst estimate windmill don't even get to half a million kills, but others are much more deadly. Cats, for example, kill more than 3,000 birds, for every one a wind mill does.
There is high pressure in front of the blade and low pressure right _above_ it. However this effect doesn't make much difference to large objects like birds.
Nope. The down wind side is typically lower speed, higher pressure. The wind turbine works because the combination of wind and rotation creates a low pressure side up-wind/up rotation that sucks the blade forward. That suction also captures birds. Think Bernoulli.
Cats catch the prey end of the avian food chain. Windmills typically kill the predator end. And there are MANY more prey birds than predators. And anyone that hasn't at least pasted a hawk silhouette on their windows or taken some other anti-bird strike action should be ashamed of themselves.
Do you realize you are telling that wind machines are air compressors? - Compressing the lower up stream pressure to the higher down stream pressure? Compressors REQUIRE energy do not generate it. Yes the back side (down wind) of the wind machine has reduced air speed. That lower kinetic energy is the result of the wind machine extracting energy from the air flowing thru it; however, you will not get both energy and more compressed air as you claim the down wind side is. Please Register or Log in to view the hidden image! Some of the energy stored in high pressure air (right side of this drawing) flow can be converted into Kinetic energy of higher speed air as you see on the left side, but the air pressure is reduced, again a you see here. This is a demonstration of the Bernoulli effect but REQUIRES energy input - does not produce energy as wind machines do. - you have things exactly backwards.
