Author Topic: Report KD 598 about a floating water turbine availabe  (Read 7067 times)

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Adriaan Kragten

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Report KD 598 about a floating water turbine availabe
« on: June 21, 2017, 10:27:29 AM »
Public report KD 598: "Ideas about the 3-bladed VIRYA-0.65 water turbine with 20 degrees inclined shaft coupled to the generator of the VIRYA-2.68 windmill for 12 V battery charging", from November 2015, can be copied for free from my website: www.kdwindturbines.nl at the menu KD-reports.

This report describes a floating water turbine which is coupled direct drive to the PM-generator of a windmill for which a measuring report (KD 78) is available. The 0.65 m diameter rotor of the water turbine is designed using the same theory as also used for wind turbines and the characteristics therefore can be estimated accurately. The construction is rather simple but has not yet been tested.

keithturtle

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Re: Report KD 598 about a floating water turbine availabe
« Reply #1 on: June 21, 2017, 07:28:19 PM »
The attached report addresses some of the complexities of extracting power from a moving stream.  Probably makes sense to get the most velocity you can to drive the impeller.

Somewhere I saw a spiral VAWT-looking impeller that claims to get more energy than a propeller type, but can't find it just now

Turtle
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Adriaan Kragten

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Re: Report KD 598 about a floating water turbine availabe
« Reply #2 on: June 22, 2017, 05:21:19 AM »
I have looked at the article about ducted water turbines. It is true that the water speed can be increased by a well designed venturi and ducting the rotor also has as advantage that the rotor can't touch the bottom of the river. However, manufacture of such a venturi is a lot of work, rather costly and it requires special skills. So I think that one should do this only for rather large designs.

In report KD 598 I have described an option for which I think that it can be made by almost every small workshop. It is meant for 12 V battery charging and in figure 6 of KD 598 it can be seen that even for low water speeds, an acceptabel power is supplied for a single house hold.

Adriaan Kragten

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Re: Report KD 598 about a floating water turbine availabe
« Reply #3 on: May 22, 2018, 01:27:01 PM »
Report KD 598 has been reviewed. Some small mistakes have been corrected and a new part is added to chapter 6. This new part gives the characteristics for star rectification and 24 V battery charging.

Adriaan Kragten

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Re: Report KD 598 about a floating water turbine availabe
« Reply #4 on: June 03, 2018, 09:58:22 AM »
A new chapter 7 has been added to report KD 598 about the VIRYA-0.65 floating water turbine. In this chapter it is investigated if the matching in between rotor and generator can be improved by taking a simple 2-bladed rotor with a slightly smaller rotor diameter of 0.625 m in stead of 0.65 m and a design tip speed ratio of 3.5 in stead of 3. The matching of this VIRYA-0.625 for 26 V battery charging and star rectification of the original 230/400 V winding is better than for the VIRYA-0.65. The better matching results in reduction of the cut-in water speed from 0.7 m/s up to 0.6 m/s. The starting water speed is increased from 0.37 m/s up to 0.5 m/s but, as it is still lower than the cut-in water speed of 0.6 m/s, this is no problem. The maximum power at V = 2 m/s is 160 W, so the same as for the VIRYA-0.65. The negative effect of the slightly smaller rotor diameter is compensated by the better matching.

JW

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Re: Report KD 598 about a floating water turbine availabe
« Reply #5 on: July 08, 2018, 08:46:10 PM »
Adriaan

One thing you may consider is your attachments especially, you are not archive the links. You can attach your pdf here on this forum.

I can fix this for you.  Consider that the attachment feature can support pdf

JW

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Re: Report KD 598 about a floating water turbine availabe
« Reply #6 on: July 08, 2018, 09:08:50 PM »
Here is an example of how we at Fieldlines can archive your work once you attach a PDF, look to the BOTTOM of the page for a link hit that and your PDF will open. It will say "open" "save" I just hit open and the PDF will open.
« Last Edit: July 08, 2018, 09:23:13 PM by JW »


Adriaan Kragten

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Re: Report KD 598 about a floating water turbine availabe
« Reply #8 on: July 15, 2018, 02:49:24 AM »
Here is an example of how we at Fieldlines can archive your work once you attach a PDF, look to the BOTTOM of the page for a link hit that and your PDF will open. It will say "open" "save" I just hit open and the PDF will open.

I know that I can add a report as a link but I don't do this for a whole report. Sometimes I have done it for a single picture. If a report is only available at my own website, you always get the latest version. If I modify a report, there is some change in the name of the link and this change is not made in the link on an other website than my own. So to get the latest version of one of my reports, you always have to go to my website: www.kdwindturbines.nl.

JW

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Re: Report KD 598 about a floating water turbine availabe
« Reply #9 on: July 15, 2018, 10:50:49 AM »
Thanks for your reply, I  was just wondering no problem.   

keithturtle

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Re: Report KD 598 about a floating water turbine availabe
« Reply #10 on: July 17, 2018, 01:36:55 AM »
mr. turtle, you mean the gorlov device?


The very same.  Thank you for finding it; now if I could only build it

Turtle, still at it
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Ungrounded Lightning Rod

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Re: Report KD 598 about a floating water turbine availabe
« Reply #11 on: July 20, 2018, 12:51:36 AM »
Hi Adriaan:

You might find this link useful:

http://www.math.le.ac.uk/people/ag153/homepage/Gorlov2001.pdf

It's a paper by Gorban, Gorlov (yes, THAT Gorlov), and Silantyav, deriving limits (GGS model) similar to the Betz limit for substantially planar kenetic-energy harvesting turbines in unconstrained flows of INcompressible fluids (i.e. propeller-like turbines in water that's flowing freely, with negligible head, in a broad stream rather than a duct the size of the turbine).

They say Betz substantially overestimates efficiencies in water and come up with a limit of about 30.1% for essentially planar turbines (like propellors), though three-dimensional structures can go higher.

Your KD 598 describes a Garman turbine (propeller-like turbine on an angled shaft below a raft), which tend to run between 15 and 18%.  You're a razor-hair under 15%, which is right in the ballpark, and good work for an easy to construct rotor (rather than something with a highly-optimized waterfoil shape).

The (then recently characterized) Gorlov turbine runs about 35% (and was the top of the line by a bunch).

It's essentially a water version of a helical darrieus, with supporting disks at the top and bottom that constrain the water from entering or exiting except through the blade-swept space.  But for water the blades are much wider - about half as wide as the spaces between them.  As a helical it doesn't vibrate substantially and self-starts.  As a broad-bladed, high-solidity design it can harvest substantial energy from slow water flows.

Looks to me that a vertical-axis Gorlov should be easy to construct (using, for instance, the same technology as fiberglass or wooden boat hulls), would be sturdy, would hang straight down from, and be entirely under, a supporting raft, would harvest more than twice the energy as a propeller-like turbine for a given swept area and (being rectangular) would have a substantially greater swept area, and would probably move slowly enough, visibly enough, and with enough pressure disturbances to trigger the lateral-line sensors, to be detected and avoided by fish.

The main problem would be supporting it against the side-forces trying to bend the axle, which would require either an underwater bearing at the bottom of the shaft or a strong shaft and two separated bearings above water.  (The Garman is easier to support from above because the rotor loads its shaft almost entirely in tension, so even if you do use a cutlass bearing underwater it only has a tiny load, while the Gorlov would need a bearing that could support half the drag.)

The paper doesn't give the details of constructing a Gorlov rotor.  But it should be easy:  Like a Darrieus, it should work well with any decent, low-resistance waterfoil shape that lets the flow attach to the front from a modest angle and attached flows leave the back tangent to the circumference and with negligible turbulence.  With a vertical shaft the generator and transmission or belts would all be above water and easy to shield from both splash and rain.
« Last Edit: July 20, 2018, 12:29:19 PM by Ungrounded Lightning Rod »

keithturtle

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Re: Report KD 598 about a floating water turbine availabe
« Reply #12 on: July 21, 2018, 02:08:30 AM »


Looks to me that a vertical-axis Gorlov should be easy to construct (using, for instance, the same technology as fiberglass or wooden boat hulls), would be sturdy, would hang straight down from, and be entirely under, a supporting raft, would harvest more than twice the energy as a propeller-like turbine for a given swept area and (being rectangular) would have a substantially greater swept area, and would probably move slowly enough, visibly enough, and with enough pressure disturbances to trigger the lateral-line sensors, to be detected and avoided by fish.

That's what I thought when I saw it mentioned years ago.  But if the stream was low flow, wouldn't the horizontal arrangement be preferred?  With enough diameter (and more than three blades) the axle and drive could stay dry, and still let creatures through without smashing them.

Turtle
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Ungrounded Lightning Rod

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Re: Report KD 598 about a floating water turbine availabe
« Reply #13 on: July 22, 2018, 03:58:51 PM »
But if the stream was low flow, wouldn't the horizontal arrangement be preferred?  With enough diameter (and more than three blades) the axle and drive could stay dry, and still let creatures through without smashing them.

In a shallow but wide stream, horizontal axis can sweep more water.

But how does the axle and drive stay dry?  Do you have less than half the rotor submerged?  I'm not sure how well that works.  (If it's NEARLY half-submerged it might not be all that much worse than a fully-submerged configuration, but that's a guess.)low momentum, which, in this case, would send it straight up.

= = = =

Looking around I find that NACA 0018 seems to be the default blade profile for Gorlov mills, both air and hydro.  For instance, https://www.pmu.edu.sa/Attachments/Academics/PDF/UDP/COE/Dept/ME/Helical-Wind-Turbine.pdf says:

Quote
We  decided  to  go  with  NACA  0018  blade  profile  as  it  was  used  frequently  in  wind  and marine   helical   turbine,   NACA   0018   blade   offers   a   medium   between   the   optimized performance of  a thin blade and the manufacturability and durability of thick blades profile.
« Last Edit: July 22, 2018, 08:33:38 PM by Ungrounded Lightning Rod »

keithturtle

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Re: Report KD 598 about a floating water turbine availabe
« Reply #14 on: July 22, 2018, 08:17:28 PM »
But how does the axle and drive stay dry?  Do you have less than half the rotor submerged?  I'm not sure how well that works.  (If it's NEARLY half-submerged it might not be all that much worse than a fully-submerged configuration, but that's a guess.)

That was the thought, like, a large poncelet wheel with only the airfoil portion submerged in a restricted channel to increase velocity, maybe 30% submerged at most.  There would be at least a dozen blades

I have a 24" wide drag wheel built for that purpose, but the stream flow is rather limited so it would need pinched down in an accelerating channel to be of much value

Turtle
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Ungrounded Lightning Rod

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Re: Report KD 598 about a floating water turbine availabe
« Reply #15 on: July 22, 2018, 08:32:12 PM »
But how does the axle and drive stay dry?  Do you have less than half the rotor submerged?  I'm not sure how well that works.  (If it's NEARLY half-submerged it might not be all that much worse than a fully-submerged configuration, but that's a guess.)

That was the thought, like, a large poncelet wheel with only the airfoil portion submerged in a restricted channel to increase velocity, maybe 30% submerged at most.  There would be at least a dozen blades

I have a 24" wide drag wheel built for that purpose, but the stream flow is rather limited so it would need pinched down in an accelerating channel to be of much value

Turtle



I expect it would splash a LOT, as it deflects the flow to be tangent to the circumference of the blade path, so on the side where the blade is entering the water the deflection would create a jet almost straight up.

Once it's up to speed, most of your thrust comes from the segment of the blade path near the center, i.e. at axle height if the axle is horizontal.  That's where the water has its flow angle changed the most.  All its forward momentum is redirected as crossflow momentum, which, in this case, would send it straight up on one side straight down on the other.  At the edge(s) of the swept area the water's path isn't deflected at all and all you get is drag.

Water thrown into the air (and not caught and redirected again) is energy lost.

Adriaan Kragten

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Re: Report KD 598 about a floating water turbine availabe
« Reply #16 on: July 27, 2018, 04:02:25 AM »
For the derivation of the maximum power coefficient for a wind turbine, Betz has assumed that the medium is incompressible. So Betz has assumed that the product of the wind speed and the area is constant for every cross section of the stream tube. In reality there is a small increase of the pressure in front of the rotor and a small decrease of the pressure behind the rotor but if you calculate the average pressure difference over the whole rotor for moderate wind speeds and for a normal thrust coefficient of about 0.75, you will find that this pressure difference is very low. Water is really incompressible and therefore you will find the same maximum theoretical Cp of 16/27 as for air.

The real maximum Cp is much lower than the Betz coefficient because of wake rotation, tip losses and airfoil drag and because the blade is not effective up to the center of the rotor. These effects are explained in chapter 4.3 and in formula 6.3 of my report KD 35. I don't see a good reason why these four effects are stronger in water than in air. For fast running rotors, airfoil drag is the main reason why the real Cp is lower than the Betz coefficient. An advantage of water is that the kinematic viscosity is much lower than for air and this results in a much higher Reynolds number for the same speed and chord. Therefore even at low water speeds and at small blade chords you will get acceptable high Reynolds numbers. The Cd/Cl ratio normally decreases at increasing Reynolds number so a high Cd/Cl ratio will not be a reason for a low Cp of a water turbine.

Practice will be the final prove so it will be a good test if someone would really build and test the described water turbine.