Has anyone fitted laminar airflow generators to their mast ?

[Dave_S]

It seems like the wrong description in the YouTube video (vortex generators), the idea is to create Laminar flow from turbulent flow. We used them on race cars as well but the video of an aircraft wing looks pretty impressive.

So I was wondering if it might help the transition from mast to sail ?



https://youtu.be/SXwVyxorvno

[Singularity]

I'd suggest that for practical purposes to consider airflow to be laminar before it runs into anything, so we don't exactly create laminar flow. Furthermore, what we'd like to do with our airfoil/sail is to keep the airflow laminar for as long as possible as turbulence lends to separation/drag. We want to trick the wind into working for us without it knowing we're there.

So while the mast sort of disrupts baseline laminar airflow before the flow reaches the sail, in a boat we have a lot of control over the shape of the foil, where airplanes have limited capacity to change the shape of the foil, and race cars have practically zero ability to change things. Moreover, on a boat we have telltales to let us know how good we're doing getting by unnoticed.

So I'm not sure what is the perceived benefit of VGs on the mast. VGs produce a little drag with the payoff of, if installed correctly, more lift/less drag literally downstream. But if engineered/installed wrong, adding VGs just give your more drag. In any event they will shred anything that brushes against them.

Perhaps you're proposing that the VGs can make the mast...mast/luff junction less draggy? On a related note there's the zig-zag tape to look into (forget the name) but it seems that there's very, very little potential payoff. Further tangent, check out this plane. As designed it has the awkward looking 'tiny wing in front of the main wing' to direct flow/increase lift...but it was draggy and folks just built them without the front slat...and added VGs to the main wing...and got pretty near the same performance.

[Dave_S]

Originally Posted by Singularity

I'd suggest that for practical purposes to consider airflow to be laminar before it runs into anything, so we don't exactly create laminar flow. Furthermore, what we'd like to do with our airfoil/sail is to keep the airflow laminar for as long as possible as turbulence lends to separation/drag. We want to trick the wind into working for us without it knowing we're there.

So while the mast sort of disrupts baseline laminar airflow before the flow reaches the sail, in a boat we have a lot of control over the shape of the foil, where airplanes have limited capacity to change the shape of the foil, and race cars have practically zero ability to change things. Moreover, on a boat we have telltales to let us know how good we're doing getting by unnoticed.

So I'm not sure what is the perceived benefit of VGs on the mast. VGs produce a little drag with the payoff of, if installed correctly, more lift/less drag literally downstream. But if engineered/installed wrong, adding VGs just give your more drag. In any event they will shred anything that brushes against them.

Perhaps you're proposing that the VGs can make the mast...mast/luff junction less draggy? On a related note there's the zig-zag tape to look into (forget the name) but it seems that there's very, very little potential payoff. Further tangent, check out this plane. As designed it has the awkward looking 'tiny wing in front of the main wing' to direct flow/increase lift...but it was draggy and folks just built them without the front slat...and added VGs to the main wing...and got pretty near the same performance.

Thanks

I expect the airflow around, and in transition from mast to sail is awful and would be costly in drag and potential lift. So I figured if there were gains to be made someone will have found a solution and found the video I attached when looking to see if there had been work done on it (other than rotating masts)

I couldn't get your link to work.

[a64pilot]

VG’s work by adding energy to the airflow, the energized airflow for whatever reason will stick to a surface with greater tenacity than non energized air will.

So where would you put the VG’s? On an aircraft wing they are not placed on the leading edge which is where the mast is, but they are placed pretty much at the max wing thickness which is close to the center of lift for a wing, on a sail boat that would be on the sail itself about 20% or so back from the leading edge.

If you look at Commercial airlines, you will almost never see full span VG’s, you will se some strategically placed to fix problems, they are a band aid.
VG’s are not magic, they have downsides, there is no free lunch.

Do the ultra high performance boats that have double surfaced wings for sails have VG’s? I have no idea myself, but speculate that if they do, maybe there is some gain from VG’s.

VG’s effects aren’t as well understood as you may suspect, most often especially on automobiles they are a styling feature more than anything else, a lot like carbon fiber pieces are.

I did some testing on VG’s effects on the spray pattern of agricultural aircraft with some interesting results.

I’d suspect that for VG’s to accomplish anything on a sail boat, you would have to have a rotating mast so that the relationship between the mast and sail wasn’t a constant variable, otherwise I’d suspect that VG’s on a mast would work at one specific wind angle and at all other angles they would just get in the way.

[tkeithlu]

Ahmen, A64, although I suspect that you meant "add velocity" rather than "add energy." You can mess with airplane wings because you have fewer variables in a fixed airfoil, angle of attack being the major one. Sails are just too flexible for that. If you want to invest in reducing drag, convert to tear-drop cross section standing rigging, because round rigging (has a high Reynold's number) induces suprisingly high drag.

Yeah, the image of your flapping sail hitting those sharp blades is painful even to think about.

[valhalla360]

If you want to keep the flow laminar, a rotating wing mast is an option...though it comes with it's own set of complications.

Vortex Generators would be in the realm of Americas Cup boats if you had any realistic hope of getting a measurable benefit out of them. Even then it could turn into a black hole that creates no real benefits.

On your typical cruising boat, there are a lot of more effective solutions to improve performance.

[Scaramanga F25]

Yes, I have seen these on a 1970-80 IOR boat mast. They did not catch on.
The thin metal laminar flow generator strips were glued on each side.

[guyrj33]

In the video the only attribute attributed to the vortex generators was reduced stall speed. Effectively widening the useable angle of attack at the relatively slow speeds shown in the video.
When we want our sails to work better in low velocity winds, we make them fatter.
I wonder if the real effect of the VG's is to increase leading edge turbulence thereby making the wing look like it has a deeper chord.

[guyrj33]

I think the best laminar flow generator most of have is our headsail.

[zstine]

Originally Posted by guyrj33

In the video the only attribute attributed to the vortex generators was reduced stall speed. Effectively widening the useable angle of attack at the relatively slow speeds shown in the video.
When we want our sails to work better in low velocity winds, we make them fatter.
I wonder if the real effect of the VG's is to increase leading edge turbulence thereby making the wing look like it has a deeper chord.

If the wing stall is reduced from 60knts to 45knts with the VGs, and the airplane weight, air density, etc has not changed, then wouldn't you say that if that wing were mounted vertically on a boat, it would create more lift at say 45knts with the VG's than without? 15knts seems like a huge change in stall speed! I wonder if they sell these... would be easy to fake this video.

Perhaps the VGs create a boundary layer which helps the flow remain laminar...?

[guyrj33]

Originally Posted by zstine

If the wing stall is reduced from 60knts to 45knts with the VGs, and the airplane weight, air density, etc has not changed, then wouldn't you say that if that wing were mounted vertically on a boat, it would create more lift at say 45knts with the VG's than without? 15knts seems like a huge change in stall speed! I wonder if they sell these... would be easy to fake this video.

Perhaps the VGs create a boundary layer which helps the flow remain laminar...?

On a modern jet, there are adjustments made to the leading edge of the wing to increase the cord and thereby reduce the stall speed. Pretty sure it also increases drag..
On a sailboat we ease the out haul, take some bend out of the mast and ease the halyard to fatten up the main and change the chord location.
I seriously doubt any good will come from increasing drag on the luff of the main.

[a64pilot]

Originally Posted by tkeithlu

Ahmen, A64, although I suspect that you meant "add velocity" rather than "add energy." You can mess with airplane wings because you have fewer variables in a fixed airfoil, angle of attack being the major one. Sails are just too flexible for that. If you want to invest in reducing drag, convert to tear-drop cross section standing rigging, because round rigging (has a high Reynold's number) induces suprisingly high drag.

Yeah, the image of your flapping sail hitting those sharp blades is painful even to think about.

Nope I meant add energy, look it up, they energize the airflow, the turbulent energized airflow will stay attached to the surface far longer than laminar airflow will.

https://www.boldmethod.com/learn-to-...ex-generators/

The holy grail used to be laminar airflow, flush rivets and polished surfaces, but that isn’t always faster, sometimes now a rough surface is faster, have a thin layer of air be trapped against the surface and the air shear against itself as opposed to shearing against a polished surface is often less drag.
So far as meaningful drag reduction from aerodynamic shapes, at the speeds we are talking about here, it’s not likely to mean much.

Sometimes what works at 500 kts, doesn’t at 5 or even 20.

[StoneCrab]

No offense but the premise presented for the use of vortex generators is misunderstood.

A laminar airfoil is highly efficient but suffers from a sudden loss of lift when the ideal angle of attack is exceeded. The sudden air ripping away from the airfoil is accompanied by shock waves which are very expensive in terms of energy loss.

The vortex generators disturb the boundary layer and provide a more gradual transition into a stall condition.... read that as giving the pilot some warning, rather than a sudden loss of control. It also reduces the energy losses by reducing the shock waves.

Non laminar wings can maintain some amount of lift well into a stall, providing a loss of the ability to maintain altitude, but generally with very little feeling of a loss of control.

A laminar wing aircraft will stall violently without vortex generators. Since it is atypical for both wings to stall exactly at the same moment, this sudden and often violent loss of lift, and huge increase in drag, can provide some interesting gyrations.

Most commonly the sudden dropping of one wing. Normal pilot input to correct is opposite aileron which drops the outboard control surface on the falling wing further aggravating the stall of that wing. As that wing falls and slows, the opposite wing speeds up, gaining lift, flipping the plane on its back as the airplane enters a spin.

The aircraft discussion is more for entertainment, but it is relevant. While a mast may be aerodynamically dirty, an entirely laminar "wing" profile wouldn't be a solution either. You would experience sudden stalls if the sail trim wasn't maintained at all times. This would suck, so vortex generators would probably be added anyway. My conclusion is that a mast is one big vortex generator for the cloth sail. No matter what they tell you at the loft, a fabric sail will never be laminar.

[zstine]

Originally Posted by StoneCrab

No offense but the premise presented for the use of vortex generators is misunderstood.

A laminar airfoil is highly efficient but suffers from a sudden loss of lift when the ideal angle of attack is exceeded. The sudden air ripping away from the airfoil is accompanied by shock waves which are very expensive in terms of energy loss.

The vortex generators disturb the boundary layer and provide a more gradual transition into a stall condition.... read that as giving the pilot some warning, rather than a sudden loss of control. It also reduces the energy losses by reducing the shock waves.

Non laminar wings can maintain some amount of lift well into a stall, providing a loss of the ability to maintain altitude, but generally with very little feeling of a loss of control.

A laminar wing aircraft will stall violently without vortex generators. Since it is atypical for both wings to stall exactly at the same moment, this sudden and often violent loss of lift, and huge increase in drag, can provide some interesting gyrations.

Most commonly the sudden dropping of one wing. Normal pilot input to correct is opposite aileron which drops the outboard control surface on the falling wing further aggravating the stall of that wing. As that wing falls and slows, the opposite wing speeds up, gaining lift, flipping the plane on its back as the airplane enters a spin.

The aircraft discussion is more for entertainment, but it is relevant. While a mast may be aerodynamically dirty, an entirely laminar "wing" profile wouldn't be a solution either. You would experience sudden stalls if the sail trim wasn't maintained at all times. This would suck, so vortex generators would probably be added anyway. My conclusion is that a mast is one big vortex generator for the cloth sail. No matter what they tell you at the loft, a fabric sail will never be laminar.

While what you say sounds logical, that VG 'soften' the transition to stall, The video clearly demonstrates a significant increase in lift by reducing onset of stall from 60 to 45knts. The VG adds drag, but the turbulent boundary layer delays flow separation increasing max lift.
The following is a quote from an areodynamicist comparing Mylar sails to dacaron:

"Under your assumptions, the difference would be seen in the boundary layer development due to the difference in roughness between the Dacron and Mylar surfaces. The smoother Mylar will have laminar flow over a greater distance than the Dacron sail, with its stitched seams and woven texture. This may lead to less lift for the Dacron sail, due to a thicker boundary layer. Or it may lead to higher maximum lift if the turbulent boundary layer delays separation. It depends on the sail shape and the operating conditions."

[StoneCrab]

You and I may be the only two on CF that are interested, but since I like a challenge and never assume that what I think is 100 percent accurate, I like diving into these topics. To that end, I put the question to a university student studying aerodynamics. I hope you find it as interesting as I did.

Here's what he said:

You are correct, his statement "create laminar flow from turbulent" is incorrect. Actually, vortex generators accomplish the exact opposite. I can't blame the guy though, this isn't an easy science. There is a lot to unpack but I'll try to do it concisely.

Vortex generators are placed in laminar flow and create turbulent flow. This may seem counterintuitive, but the way I think of it is they actually "add energy" to the airflow in the form of swirl. This swirly turbulent airflow is able to remain attached to the surface for longer. What is swirl? Imagine a perfectly swirled ice cream cone or the water in your toilet going around the bowl when flushing... the vortex generator creates this swirl motion in the airflow. We want this swirl motion because it "grabs" high energy airflow above the surface and carries it down to the surface of the wing. When we talk about stall, turbulent flow actually is NOT the issue. I put a picture here to describe a bit:



We can see laminar flow transitions into turbulent flow about midway through, but this is fine. What we are worried about is called "boundary layer separation". This occurs in the section I marked with red and this separation is what causes stall. Let that separation get too big and we lose all lift because we have no airflow over that section of the wing. We use vortex generators to essentially increase airflow near the surface of the wing and push back or minimize that separation (in red).

In the car world, vortex generators are used to increase airspeed over their inverted wings - increasing downforce for better handling. The issue is these vortex generators have to be well placed. It is not enough to just throw some randomly on your car.

As for a sailboat, if I were him I would look up if anyone else has done it. If it is actually helpful, I would think racers would already be doing it. I don't see the harm is testing it out, but I don't think he would see a tangible benefit. Since you aren't worried about stall on your sails, the only benefit would be a decrease in drag. If possible the VGs would work best about 1/4 of the way behind the leading edge of the sail (instead of on the mast).