Windmill or Wind Turbine- powered boats: how many are out there, and are they viable?

Interesting video of land based wind car...

http://ing.dk/artikel/90235?nyhedsbrev

 

Michael
The language is not something I can appreciate but the vehicle is well engineered. Maybe a little heavier than it could be. The low drag fairing is certainly worth the effort.

I think the fan cowling is more for physical protection than any aerodynamic benefit.

Rick

 

Here is a bunch of examples of these wacky vehicles...

http://www.windenergyevents.com/

Apparently this is going to be a regular event from now on.

 

Michael, are you trying to say that a tube aligned with the airstream with such and such an internal shape has zero drag? I might not be understanding what you're trying to say but it kind of sounds like that is what you're implying.. (wrt Post#240)
Also i am very confused about your recurring use of the word supersonic. I can't imagine you're seriously thinking about such a level of augmentation that you're going to turn an ordinary breeze into a supersonic torrent????
Besides, L/D ratios tend to drop as soon as one enters compressible flow range, those shock waves eat up a lot of energy..

Anyways, thanks for the interesting links.

 

Supersonic?

Tcubed

I'm not sure where you saw me use the word supersonic, I did say the speed of sound though. Tip speeds can reach supersonic speeds, but I don't think that is a useful regime to operate in. Going supersonic is wasteful to my way of thinking, and would never recommend it for any purpose other than blasting dirt and oil off of a grungy driveway. What I did say, or allude to, is that the venturi duct is free of shape or wave drag up to the point it goes SONIC at the throat. Beyond that it is useless as a free flowing flow collimator, and reverts to the physics of a fireman's hose. I was stating what the limits are, as a scientific principle, not what is going to happen in a 3 MPH breeze. If you want to look more closely at this idea I suggest you look at this Wiki entry.

http://en.wikipedia.org/wiki/Busemann's_Biplane

Michael

 

Comparisons

Tcubed

Here is a plot using Hepperles JavaFoil showing the difference between a venturi duct and a streamlined car at 200 MPH. Notice that there is no wake behind the venturi, but the car has pressure waves around it entending all the way to the edges of the field. Both objects are sitting side by side in the same flow.

Michael

 

Ok. So what do you think the coefficient of drag is? That's the bottom line so i can calculate whether or not it is beneficial.

On a given section of turbine blade the axial force resolves as
A = Lsind + Dcosd where L is the lift force of that section D is the drag force and d is the angle between the real wind (or the axis, presuming they're aligned as they should be) and the apparent wind at that particular section of blade.
T = Lcosd - Dsind is for the tangential force on a section of blade
Also the power in watts of a given airstream of cross sectional area S and flow velocity V is P = 0.5*rho*S*V^3
That's for anyone who might be interested and not have those formulas handily written down already...

 

What is drag?

Tcubed
(Let me first state that this like many other forums on cutting edge ideas is not the answerman, but an attempt to discover principles and methods that could break new ground in new or overlooked technologies. I certainly don't have a set of ready made rules to plug numbers into that could solve problems by juggling numbers. Before we can even begin to do that we need a concept which addresses the flaws in existing methods, and not just another optimization of existing imperfect approaches.)

I wish I knew clear answers to your questions, but since everyone and his mother has studied external flows to death, and no one has bothered to look into internal venturi ducting, there are few convenient formulas to pick from. That is why I choose to investigate this on an emperical and intuitive level, since it makes more sense to try and visualize what is happening on a molecular level first. To give you my perspective, let me explain how I view drag on a moving object first, and why a duct is ultimately a superior way to solve some aerodynamic situations.

First, air consists of countless molecules that are in effect tiny elastic spheres that are typically travelling at 1000 feet/sec or so. If we could remove all the air molecules but one, and watch it move, it would seem to follow the exact path of a cannonball, namely a parabolic arc that brings it back to earth ultimately. However, it shares space with countless others, and well before it falls to earth, it will strike another in a violent collision. This collision will resolve any differences in momentum the two might have. In an ideal atmosphere, consisting of identical molecules, and without any thermal inclines etc., this would eventually result in all molecules with about the same velocity. We call this stagnant air. If for instance, one of these molecules is disturbed, and has a greater velocity than its neighbors, it will impart this excess momentum to them, and they in turn to others, and on and on, until it has dissipated over a immense fan shaped volume. This occurs at the speed of sound, because they are all moving at that speed, and has the appearance of a wave emanating from the point of disturbance. Once this wave is set into motion, it cannot be recalled, and in theory travels to infinity.

Let us now examine an embeded object such as a sphere that has some motion with respect to this gaseous medium. On the forward facing surface there are collisions between the object and the atmosphere, and exchanges of momentum are taking place, the gas is trying to reverse the course of the object and vice a versa. It is clear that on the front surface the relative velocity is the sum of their respective velocities, and on the back side they are the difference. Ahead therefore, is a positive pressure wave of momentum energy rippling away, and on the back a rarefaction wave. If the relative motion is small, for instance at the speed of a person walking, the difference between the front and back are too small to measure, but the faster you go, the worse this gets, because sooner or later the air doesn't have enough velocity to fall in behind, and separation occurs and no collisions happen on the backside. The energy absorbed by the air in front is radiating away ahead of the object at the speed of sound, and is 1000 feet minus the speed of the object ahead of it one second later. This energy is unrecoverable, and is an artifact of every object that moves through the atmosphere. Bats and birds use it to locate their prey by their acoustic signature.

Subjectively, the sphere experiences this force as drag, because if some force were not supplied to replace this lost momentum, it would before long come to rest. If we continue this scenario up to the speed of sound, we have the condition where on the front the relative velocity is 2000 ft/sec and on the back 0 ft/sec. (this is somewhat of a simplification, but you get the idea). Whatever the exact math that describes this, it is obviously some exponential function. One thing is clear, massive amounts of energy are going to be expended keeping any object moving at a significant fraction of the speed of sound. This is because the forward bow wave is dispersing into an almost infinitely large plenum with almost infinite heat sink capacity. Keep in mind, this bow wave is well disguised heat! Turning this sphere into an ellipse or a smooth teardrop doesn't change anything about this, except the magnitude of the variables.

This situation does not occur in a venturi, because the external body is a perfect streamline, which has no wave drag, and the internal duct surfaces reflect the wave disturbance in upon itself, and concentrate this energy instead of dispersing it. This culminates at the throat where the maximum focussing effect occurs depending on the geometry and and other physical conditions. Since from an external viewpoint this appears as a gaping hole with air rushing into it it seems as though it is a giant vacuum sink, which projects a rarefaction ahead of it instead of a pressure wave. Fluid dynamic plots clearly show this draw into the duct from a considerable distance ahead of it. Since the 'flow' can move at a signifcant fraction of sonic velocity, it is hard for pressure disturbances to work their way back upstream, and totally impossible at the throat. Whatever energy bounces off of airfoils and such in this channel can only richochet around off other internal surfaces, and so is not lost because it is a closed system. That is why jet turbines are so efficient even though they have jillions of blades in them. On the diffuser end, the flow is expanding spatially and exerts pressure against the walls in a manner which cancels the forces developed at the inlet. What ever the case may be, there exists at the throat a flow regime that can be jacked up to subsonic speeds with very little impedance, where foils and such could be employed to extract a fabulous amount of energy, although it may be a bit more complex than a simple propeller in the slipstream.

If you have simple lift to drag relationships you can identify for this, please feel free to share them. As for myself, I am an engineer and an inventor, who happens to be a sailor as well, and I believe if it were a simple matter of a little more or less twist on a prop we would already be sailing the oceans on generators. Just as a jet engine uses all the same principles as a propeller, it doesn't look at all like a propeller because some clever persons were able to configure it as a complex machine to do a task to perfection. My goal is to find that arrangement, not to polish up existing technical strategies that don't solve the problem.

Michael

 

Excellent post.

I applaud the use of intuition to resolve problems as well as looking into 'outside the box' solutions, however, sometimes intuition alone can lead one to false conclusions especially when it is something as impalpable as complex air flows. Hence i favour a blend of intuition and testing, with the rigorous logic of mathematics.
My specialty is low velocity steady state Newtonian fluids.
The way one analyzes this type of flow is by making some simplifications to the most general equations that will allow them to be solved, yet are detrimental to the accuracy of the result that is for all practical purposes, less than the accuracy of the measuring equipment (in other words immeasurably small differences)
The first is that a fluid is a continuum. This does not affect results in any case apart from nanoscale dynamics.
Secondly that air is incompressible. This is very accurate up to about 100 M/s.
Third that the speed of propagation of pressure information is infinite. This is completely accurate apart from cases where there are abrupt time dependent changes. Steady flow implies time independence.

I must now gently correct some of your assertions.
You sent me to Busemann's biplane.. This is actually a design that has it's application in purely mach > 1 , not really relevant in our case.
Not many formulas to choose from for flows through ducts? I beg to differ, This has already been researched ad nauseam. You just got to get your hands on the right text book. Unfortunately, all my text books are stored on the other side of the Atlantic, but i will try to get them sent to me and then i could be much more helpful.
The venturi tube is essentially an obstruction to the free flow, just as ANY object is, even a zero thickness plate aligned with the flow is considered an obstruction and as such will start impeding the flow some distance upstream of the intake. It will not be 'sucking' any air in, on the contrary, the flow lines will slightly diverge around the leading edge of the venturi. They also diverge around a typical wind turbine, with the vorticity at its highest at blade tips- the infamous 'tip vortex' hence the reason for few high aspect blades. This tip vortex effect is almost completely eliminated in a duct system, but at a price. If you flare out the trailing end of the venturi then yes, you can create a convergence of flow lines but then the whole duct now has a bit more drag.

The question remains at what price?

Here is one of the most fundamental equations in fluid dynamics; scroll down to

Incompressible flow of Newtonian fluids

http://en.wikipedia.org/wiki/Navier-stokes_equation

There is further down the simplifications that can be made for incompressible flow and the expanded formula for cartesian, cylindrical and spherical coordinates. In the case of this object cylindrical is the correct choice of coordinates, but i would suggest simplifying further to 2d flow, plenty accurate enough.

On a much more down to earth level my main objection to a duct is that you can't reef it, which could be a serious problem at a certain windspeed.

I still think it is interesting to research though..

 

Michael
There is some interesting comment on this clip regarding the 2-bladed set up:
http://www.youtube.com/watch?v=IWNEXBBAGNw&feature=related

This one was the winner of the competition. Not sure if you have looked through the various videos. It suggests they have a long way to go before they better land sailing. That said I have watched a land sailor try to negotiate a road circuit and the road is very narrow when your are trying to beat to windward.

You can quickly see the benefit of gearing to take advantage of the turbine operating at its peak output.

I am keen to see testing with ducting. You cannot get something for nothing and taking energy out of the airstream in the venturi has to have far field impact. However the fact that you can beat Betz limit and also get the blades into a more efficient regime has to be a benefit. Whether it overcomes the disadvantages of the extra weight remains to be seen.

I have not checked the rules but I bet the turbines on the Aeolus racers have to be guarded at least from the side but the crude ducting would also reduce tip losses so might be neutral from a performance perspective.

I still view the turbine as a continuous energy collector and I believe best suited to electrical systems with energy storage. However I think the performance could be much improved from the current batch. Would be interesting to know the knowledge level of the students building the machines.

Rick W.

 

It is still early....

Rick,

...in the development of this field, but it is encouraging to see that someone is doing something. I saw all the material on the Aeolus Race, and I hope to be part of it next year. I am going to Holland in a month or so because my daughter started school there this summer. However I wanted to share some technical ideas and concepts that are worth thinking about, because the solution to this lies with looking at the problem the same way propeller engineers did when confronted with the problem of limiting tip speeds. Before the invention of the turbo-jet, it was thought that reaching the speed of sound was not possible because the prop tips would go sonic well before the plane could get anywhere near the sound barrier. The solution to this was not a better prop, but a 'compound prop', operating in a closed environment so that all the variables of pressure, temperature, volume and flow were completely under control. The first versions of this were pigs, they were heavy, ate a lot of fuel, and put out very little power. Today they have turbo-jets the size of watermellons that put out thousands of housepower. The same thing will happen to this technology, it will need to move on from the simple prop design, for the same reasons as aircraft moved to jets.

Yes, you are correct, there is an impact in the far afield air to consider, but the same applies to aircraft, yet they fly. Consider this very basic thing, a 250 ton jumbo jet is kept in the air, suspended against gravity, by a pulling force of less than 20 tons! Where did the 230 ton difference come from? It came from heat extracted from the atmosphere. Did it give up this heat voluntarily? Of course not, it took work in the form of traction to give the airfoils relative motion with respect to the atmosphere first. By investing 20 tons, we get a return of 230 tons. Sounds like a pretty good amplifier to me.
In a well designed glider, that ratio is nearer to 60:1.

We have the same problem with turbines as we had with props, except that everything about a turbine works opposite to a powered prop. Although it may be hard to visualize, we are using drag to create lift, which we are converting into torque, and we are generating thrust, which in a powered prop is a blessing, but in a propulsion turbine it is a curse.

Already in testing my bicycle version I can feel what the problem is very clearly. As I pedal it up to speed, it rolls very easy, almost can't feel it there, but at about 15 MPH it really comes alive, and looking back at it it is scary powerful. At 20 MPH it is a terror machine, but doesn't make any difference to the power to the total vehicle, in fact it hits a wall of impedance. Since my legs are very sensitive instruments when it comes to putting out more work suddenly, it is very easy to get a feel for what is occuring at the prop. I can sense that the chain is under huge tension, but because the prop creates as much adverse axial thrust as it creates torque, the power simply passes through a loop from the ground to prop to chain to wheel to ground to prop.....if I were to go fast enough, it would sooner or later bust the chain clean off.

My point is this, it is simply a matter of how the power vectors are pointing, which can be solved using a more complex flow management system. If you are interested, I can send you a layout of what I envision for this on your private email, as I am not that interested in defending this approach from naysayers that have preconceived ideas of what this type of thing will look like in the future.

Michael

 

The Aeolus rules.

TECHNICAL SPECIFICATIONS
WPV: WIND POWERED VEHICLE
Preliminary specifications!
1. Definition WPV
- Land based vehicle driving on wheels and steered by a driver
- Propelled by a device with spinning blades or Darius turbine coupled to the wheels
- Storage of energy allowed, storage device shall be empty at start (verifiable)
2. Driver
- Owner of driving license
- The driver may not be under the age of 18
- Minimum weight of driver 75 kg
- 2 registered drivers allowed (1 and 1 reserve)
3. Requirements Design
- Circumferential bumper, height 0.5m above ground, outside dimensions: length ≤ 4m, width: ≤ 2m
- Vertical projection of all parts shall remain within the maximum length and width of the circumferential bumper
- Maximum height of the complete vehicle is 3.5m.
- Maximum rotor area 4m2
- Minimal 3 wheels, not in line
- Manoeuvrability: maximum turning diameter 10 m
- Contact between driver and the road or wheels is not possible
- Drive train: fixed and variable speed transmission allowed
- The vehicle shall operate safely with wind from the side (all angles)
- The vehicle has an adequate steering device.
- The rotor can be stopped under all conditions
- The vehicle can be stopped under all conditions.
4. Competition
- Speed measurement by gps in the wind powered vehicles Safety
- 2 independently activated braking devices, one on the rotor and one on the wheel axis
- The rotor (blades/paddles) shall be contained inside a cage or net with a maximum mesh size of 0,1 m. The net shall be able to prevent broken blade (pieces) to be thrown off,
- The rotor shall be blocked when parking
- Provisions for towing with blocked rotor
- Head forward position not allowed
- The driver shall be able to vacate from inside without assistance
- Emergency evacuation markings on the outside of door(s)
- Roll bar and adequate protection of driver from lateral and frontal shocks
- Driver wears safety belt (buckle well marked) and helmet
- Provided with emergency strobe light with own, isolated energy supply activated by driver
- Provided with horn on pressed air activated by driver
- Cockpit shall be well ventilated
- Good visibility for the sector from -135 to 135 degrees with course
- Provided with rear view mirrors
- Dead man’s switch
Safety validation
- Design report with safety instructions to be submitted
- Graph of measured average speed depending on wind speed
- Manoeuvrability shall be demonstrated in test before the race
- Brake capacity tested shall be demonstrated before the race on a ramp
- Knowledge of applicable rules for the race shall be tested
- Vehicles that are approved are marked by the organization
5. Race
Track
- Length: 1.2 to 3 km depending on wind direction
- Race track is part of the seawall along the north sea coast
- Slope of track ≈ 5° perpendicular to the direction of driving, declining towards the sea
- Starting from a ramp with a length of more than 60 m and a slope of ≈ 3°.
- Possibility for inspection and practicing on (part of) the track before the race
Safety
- Safety escorts in front and back
- Medical team
- Fire brigade
- Tow away team
- Slow vehicles will be stopped and towed away if necessary
- Maximum wind speed for racing bf 7 (<15 m/s)
Traffic rules
- Briefing before the race
- Keep downwind side of the track
- Taking over at the upwind side
- Use the horn before passing
COLORATION
Every coloration of the wind powered vehicle is permitted. High-visibility colours are advised.
CREW SAFETY
Safety belts or restraining harnesses and/or toe clips must have clearly marked release buckles.
DESIGN REQUIREMENTS & GUIDELINES
Each team will be required to submit a basic design report that states design, construction and testing of their wind powered vehicle. Teams will not be allowed to enter the races if this report is not sent by the assigned date. WEE reserves the right to reject teams whose design is not compliant with the requirements. Modifications to the original design should be detailed and submitted to WEE.
HULLMARKING
For the purpose of identification is it obligatory that racing numbers (to be given by the organization after receipt of the Entry Form) and the name of the wind powered vehicle is featured on the hull. The racing number has to be attached to the wind powered vehicle by means of an adhesive sticker. Dimensions adhesive stickers for hull numbering: 40 x 60 centimetres. Sponsor listing is accepted.
SAFETY INSPECTION
Prior to entering the track, every day, the wind powered vehicle shall receive an inspection to ensure maximum safety. The inspections shall be performed by the arbitrators accompanied by a safety crew. Once a wind powered vehicle has passed it’s daily safety inspection, an adhesive sticker will be placed on the hull to signify compliance. Please pay close attention to any instructions given by the arbitrators or members of the safety crew. Daily inspection times will be announced in advance.

 

email:
rickwill@bigpond.net.au

 

Micheal,
I am not familiar with your Hepperles flow modeling program, but i can see it is clearly set to model an ideal fluid. I would be very interested to see the flow field when you set mu to 0.0000185 Kg/(Ms) which is the viscosity of the air. Please see if the program will allow you to input a nonzero value for mu. If it only allows kinematic viscosity then put nu = 0.000015 . Air density (just in case) is 1.23 Kg/M^3 (@18C).
Hope your program does this, it should, if it is at all serious.

 

JavaFoil

Tcubed

JavaFoil is free, here it is, play with it yourself and see how you like it. I get the same results with another program that I paid money for.

http://darwin.wcupa.edu/webapps/javafoil/

It seems to have the settings you mentioned.

Michael