Clockwise or anticlockwise: any advantage?

[DamonHD]

Hi,

I can't think of one but is there any advantage to an HAWT rotating in a particular direction as seen from the front, ie the on-coming wind?

I only ask as I visited two small windfarms today (10x ~200kW Vestas and 1x 2MW a few fields away) and all were turning clockwise as seen from the front.

If there is a convention, is it just a historical accident like roads (and thus our spacecraft) being sized in terms of the width of a horses backside (2 backsides' width per lane)?

Rgds

Damon

[DanB]

most people seem to like clockwise but it's really a matter of preferance I think. 

Lately I do think about the direction the machine furls - and in my mind it should be such that when it furls, the blades rotate such that the tips are pulled away from the tower.  That said - if you design enough blade clearance into the machine to begin with it really doesn't matter much but if the blade clearance is marginal then it's definitely an issue.

[wooferhound]

If your prop is attached to the generator using a Single Bolt or Nut, then you would want it to rotate Clockwise which would keep it tightened up.

[DamonHD]

Probably not the case for the 2MW turbine: that would be one helluva nut...  B^>

Rgds

Damon

[klsmurf]

First time poster, so sorry for jumping in, but this relates to a question I have. I've got an treadmill motor that the hub threads on counterclockwise (left-hand thread). I just made some pvc blades for it and made them to rotate counterclockwise. It made sense to me to always be " tightening " the hub. The motor generates volts both ways, but says it is clockwise rotation. Will I burn it up over time for doing this? Thanks and great forum!

[zap]

Your motor will probably be fine klsmurf... chances are they had it "driving" that way for the exact same reason you want to "drive" it the opposite way... to keep their hub screwed on tight.

[ChrisOlson]

If your prop is attached to the generator using a Single Bolt or Nut, then you would want it to rotate Clockwise which would keep it tightened up.

Unless it's left hand thread   

--
Chris

[tecker]

Righty tiighty lefty loosey is a good point you would want gears to pull in and bolts to do the same . Broken wind moves in spirals and vortexes.

[dsmith1427]

For a VAWT, a clockwise rotation will create a force in the downward direction and an anti clockwise rotation will create a force is the upward direction.  The greater the spin, the larger the force. 

For a HAWT, a clockwise rotation will create a force with the wind and an anti clockwise rotation will create a force into the wind.

The forces are created by the angular momentum of a spinning object.  If you want a visual, do a youtube search for the topic "angular momentum. 

Don

[gizmo]

Speaking from experience, if you do plan to put up more than one wind turbine, make sure they are all rotating in the same direction. The reason is purely cosmetic, windmills spinning in the same direction looks cool, pleasing to the eye. Windmills spinning in opposite directions looks bizarre, it just doesn't look right.

Glenn

[scoraigwind]

In olden times all of the 'dutch' type of windmills turned left and there was a reason for that.  The sails were rigged on long pegs that were driven right through the spars and stuck out a long way beyond toward the trailing edge.  The windmiller would hammer these pegs through the main spar, climbing up them like a ladder from the tip as he went.  Being mostly right handed, they preferred if the pegs went in from the right hand side and so the trailing edge was on the left of the sweep.  This made the sails turn anticlockwise.

Modern machines generally turn clockwise.  Some early Danish wind turbines around 1980 (windmatic) still turned anticlockwise, but then the planning authorities decided to control the direction of rotation for the comfort of the general public and decreed that all turbines must turn the same way (clockwise).

[DamonHD]

Very interesting!  Is this 'comfort' purely 'on the eye' then?

Rgds

Damon

[ruddycrazy]

When I made my 3 metre blades they turned out to be anti clockwise, with me being a left hander I was 1/2 way thru carving them before I realized. It's now been about 3 years and this weekend we had 100k + winds and the blades are still going perfect. Although my 2hp conversion is at best a 500 watt genny I noticed yesterday even with all my shed lights on and few other loads when the wind was blowing the batteries were dumping load. My battery bank is 24 volt 550 ah so my anticlockwise genny was working that good I was impressed. With my next blade sets I make they will turn clockwise and as the wind gennies will be so far apart one won't notice they are turning different directions.

Cheers Bryan

[scoraigwind]

It has been established scientifically that a landscape with turbines turning in both directions is visually disturbing to the beholder.  so planner like to try to get them all going the same way.

Other than that it doesn't make any difference except that when yawing rapidly out of the wind the blade tips get pushed toward or away from the tower by gyro forces.   For about 30 years I built machines to yaw out of the wind the 'wrong' way in that respect and I just changed the yaw direction a couple of years back so as to minimise the risk of tower strikes (although they were almost unknown anyway).   Bergey Windpower reversed the rotation of their blades for the same reason.

[Ungrounded Lightning Rod]

If you take a look at Altamont Pass in California you'll see that some models of wind turbine rotate clockwise, some rotate counterclockwise.  (It's easier to build them all the same within a model - building CW and CCW variants just about doubles your tooling.)  Each of the many wind farms there are usually all the same type.  So you get clusters of each kind.

For our stuff the main issue has been avoiding tower strikes from gyroscopic action on sudden yaw during furling.  (Unfurling is more gradual.)  As others have already noted:  If your blades end up close enough to the tower for this to be an issue you may wish to plan the direction so that furling forces push them away from the tower.  (Remember that the blades bend significantly under load - like leaf springs or a wooden bow.)

There has also been recent discussion about whether there's an issue with rotation direction vs. furling yaw direction that might degrade furling on sites where the wind is deflected upward as it hits the blades - like if the mill is on a hill.  Jury's still out on that.

[DamonHD]

OK, thanks.

On the "tower strikes from gyroscopic action" thing I am assuming that that could be made to work with either direction of blade rotation: there's no magic from being in the Northern Hemisphere that favours one direction over the other?

Rgds

Damon

[Flux]

Yes the thing is related to alternator offset in relation to blade rotation. If you reverse rotation  you need the offset on the other side to tip the blades away from the tower in yaw during furling.

This is based on the common experience that machines yaw much more quickly into furl. It is sometimes site specific and in some cases local wind conditions can produce rapid yaw when not even furling. For this specific site one rotation may be better than another but we can't cater for these factors that may not come to light until operation has been observed for a long time. Best to have enough clearance to avoid blade strike anyway but choosing offset and blade rotation to avoid strike during furl is a wise move and costs nothing.

Flux

[Ungrounded Lightning Rod]

On the "tower strikes from gyroscopic action" thing I am assuming that that could be made to work with either direction of blade rotation: there's no magic from being in the Northern Hemisphere that favours one direction over the other?

Nothing to do with hemisphere.  Everything to do with the direction of yaw vs. the direction of rotation.

When you exert force on the axle to move the axis of a spinning object, the motion reacting to that force is "carried along" with the rotation of the object and appears a quarter turn from the angle where the force was applied.  When you yaw a spinning mill one way it tries to "nod its head to look down" and the other way to "look up".  This is the gyroscopic effect.

This comes into play when you furl by yawing.  Furling is more abrupt than unfurling and also happens when the mill is spinning faster, making the gyroscopic effect stronger.  So you want it to "look up" during furling to avoid the blades striking the tower.  You accept the weaker tendency to "look down" on unfurling as an unavoidable but limited nuisance.

This means, with the typical upwind mill (blades upwind of the tower and facing the wind), you want your blades rotating so that, on furling, the blades going down are the ones being pushed upwind (and thus farther from the tower as they go through the bottom of the rotation) by the yaw.  If your furling is by the offset-rotor, tilted-tail-hinge method, it means you want the blades to be going down on the side toward the tower.

(Or just build enough tilt-back into the mill axis and/or put the blades far enough forward that this is a non-issue due to large tower-blade clearance.)