design of a diffuser/shroud for a tidal turbine (diffuser augmented turbine)

[nasir6992]

I have a problem may one of you can help me. I want to design a diffuser / Shroud for a tidal turbine. Purpose is to increase the incoming water velocity from 1 m/sec to say 3.5 m/sec or may be higher. By increasing the velocity and placing a turbine at the throat inside the shroud, will increase the power of the same turbine when it was running without the shroud. The technology is called diffuser augmented tidal turbines or shrouded tidal turbines. I want to know is there any good Naca or any other airfoils that can be used for this purpose. Any comments / suggestions on this issue. Or may be anyone of you can suggest a airfoil.

[nasir6992]

I want to design a diffuser / Shroud for a tidal turbine. Purpose is to increase the incoming water velocity from 1 m/sec to say 3.5 m/sec or may be higher. By increasing the velocity and placing a turbine at the throat inside the shroud, will increase the power of the same turbine when it was running without the shroud. The technology is called diffuser augmented tidal turbines or shrouded tidal turbines. I want to know is there any good Naca or any other airfoils that can be used for this purpose. Any comments / suggestions on this issue. Or may be anyone of you can suggest a airfoil.

[Leo Lazauskas]

Originally Posted by nasir6992

I have a problem may one of you can help me. I want to design a diffuser / Shroud for a tidal turbine. Purpose is to increase the incoming water velocity from 1 m/sec to say 3.5 m/sec or may be higher. By increasing the velocity and placing a turbine at the throat inside the shroud, will increase the power of the same turbine when it was running without the shroud. The technology is called diffuser augmented tidal turbines or shrouded tidal turbines. I want to know is there any good Naca or any other airfoils that can be used for this purpose. Any comments / suggestions on this issue. Or may be anyone of you can suggest a airfoil.

http://www.cyberiad.net/library/pdf/...per25apr06.pdf
http://www.cyberiad.net/librar/pdf/b...tonesmar03.pdf
http://www.cyberiad.net/librar/pdf/G...rt_29Jun04.pdf

There should also be some references in:

"Limitations of fixed pitch Darrieus hydrokinetic turbines and the challenge of variable pitch", B.K. Kirke and L. Lazauskas, Renewable Energy, Vol. 36, No. 3, Mar. 2011 (to appear).

"Variable pitch Darrieus water turbines", B.K. Kirke and L. Lazauskas, J. Fluid Science and Tech., Vol. 3, No. 3, June 2008, pp. 430-438.

But please don't post your request in other areas of boatdesign.net or people will ignore you as a spammer.

Now get back to work, student!

Leo.

[tspeer]

Originally Posted by nasir6992

I want to design a diffuser / Shroud for a tidal turbine. Purpose is to increase the incoming water velocity from 1 m/sec to say 3.5 m/sec or may be higher. By increasing the velocity and placing a turbine at the throat inside the shroud, will increase the power of the same turbine when it was running without the shroud. The technology is called diffuser augmented tidal turbines or shrouded tidal turbines. I want to know is there any good Naca or any other airfoils that can be used for this purpose. Any comments / suggestions on this issue. Or may be anyone of you can suggest a airfoil.

Are you looking for a section to use for the shroud cross section? I don't think a NACA wing section would necessarily be the best choice for that, unless you picked one that was highly cambered.

The first thing you need to do is to size the shroud. McCormick's Aerodynamics of VSTOL Flight has a chapter devoted to the design of shrouded propellers that would be useful to you . McCormick represents the shroud as a ring vortex at the shroud quarter chord and a control point on the shroud 3/4 chord point. The diameter of the 1/4, throat and 3/4 chord locations is then used to determine the strength of the ring vortex and the velocity at the rotor. Momentum theory is used to determine the flow through the rotor. Although McCormick develops his model for propellers, I don't know of any reason why it wouldn't work for a turbine.

[nasir6992]

Thank you for taking your time. I will look in to the technical papers.
But can you suggest any airfoil shape that has a wide inlet, deep throat and lager outlet dia than inlet. What i mean by saying that i want to use a airfoil, then i will revolve i around a centre line and make a shroud that has some inlet dia, throat dia and outlet dia. I am interested in shapes that has wide inlet dia, deep throat and outlet dia should be larger than inlet dia. I don't know wether i made my problem clear or more confussing. Thanks in advance for helping

[nasir6992]

Thanks for help. i will try to get this book and ave a look into it.
Where i can search for highly cambered airfoils ?
My shroud should be 500 mm in length and water inlet velocity is 1.2 m/sec. I want to use an airfoil that should have a wide inlet dia, deep throat and outer dia should be larger than inlet. Can you suggest me and number of airfoils (not necessary NACA airfoils anyairfoil).

Thanks for your time and help.

[tspeer]

These might be worth a look:

On the Modelling of the Flow in Ducted Propellers With a Panel Method
Potential Flow Calculations of Axisymmetric Ducted Wind Turbines (FWIW, the author of this paper became Secretary of the USAF!)
The science of making more torque from wind: Diffuser experiments and theory revisited
A Shrouded Wind Turbine Generating High Output Power with Wind-lens Technology
Performance Analysis of a Shrouded Rotor for a Wind Powered Vehicle

[nasir6992]

Thanks a lot for the help, i already have few of these papers and most of them are new for me. Thanks a lot for your time and help. I will come back if i have some queries.

Thanks a lot again .....i mean it ......

[philSweet]

This falls into the comment category. Just for grins, what would happen if you constructed a shroud which exactly mimicked the far field flow that would be found around a similar, but larger unducted turbine?

[tspeer]

I've scanned in the relevant part of McCormick's book. It's hard to discuss the topic without seeing the figures or the math.

[nasir6992]

thx for the scanned pages..........