Aerofoil underwater

Discussion in 'Hydrodynamics and Aerodynamics' started by endorium, Oct 19, 2012.

  1. endorium
    Joined: Oct 2012
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    endorium Junior Member

    Hi

    I am a student looking for some answers for area foils underwater.

    I realise in air an aerofoil will create a vortex behind it.

    Does this happen underwater? If an aerofoil is having water pushed over it will the water behind it form a vortex like effect?

    I am looking to create an output from a pump underwater that will create a turbalent flow in the waters exit from the pipe without moving parts. I though maybe an aerofoil within the pipe at the end of it may cause this?

    Any ideas are appreciated and I am sorry if this is the wrong place to ask but I cant find any forums that may be of help and I am struggling to find answers.

    Thanks for any help input you can give
     
  2. PAR
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    PAR Yacht Designer/Builder

    Welcome to the forum.

    Flow dynamics are similar in spite of the huge viscosity difference between the two mediums. As to what you're trying to do, a vane maybe cyclone shaped, wings, even just the shape of the pipe exit can accomplish what you need, though admittedly, I'm not completely sure what this is.
     
  3. endorium
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    endorium Junior Member

    Its a project for my course. I have to create an outlet from a pond\aquarium pump that outputs a turbulent flow without moving parts.

    After much brainstorming I thought if I put an aerofoil inside the pipe just before the exit it may create a vortex like when air goes over an aerofoil.

    Of course I know littl about hydrodynamics :( The pipe will only be an inch and a half wide but will have a lot of flow going through it.

    Just looking for opinions from people like yourself that actually know what they are talking about :)
     
  4. keysdisease
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    keysdisease Senior Member

    Maybe take a look at vortex generators.
     
  5. Submarine Tom

    Submarine Tom Previous Member

    The flow out of the pipe will already be turbulent.
     
  6. endorium
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    endorium Junior Member

    It will be turbulant but I want it to create an almost wave affect. Constant water out a normal pipe will not create this. I could not think how to make the water pulse out the pipe with a special pump or moving parts so creating a vortex was the next best thing
     
  7. TeddyDiver
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    TeddyDiver Gollywobbler

    Sounds like normal vorticity isn't enough for you.. Can you describe more precisely what you are after?
     
  8. endorium
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    endorium Junior Member

    I have a pump that can output from 100 gallons per hour to 900 GPH. The pipe that then enters the aquarium/pond just shoots out a constant stream of water.
    Ideally I would like some sort of pulsing affect but without moving parts I have no idea how to create this?
    If this is impossible without moving parts I was thinking of creating some sort of vertex so the water is swirling around when exiting the pipe to give a random flow to the water in the pond/aquarium.
     
  9. daiquiri
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    daiquiri Engineering and Design

    And what is the purpose of this pulsating flow?
     
  10. endorium
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    endorium Junior Member

    to create random flow from the return pump. Oxygenates the water(by creating water surface disturbance), creates a random flow in the tank/pond which mimics thre natural habitat(think waves and coral reefs) and means less pumps required internally for this flow(which means less equipment and less electricity being used).

    Usually in an aquarium you have your return pump which does nothing but pump water into the aquarium. It adds nothing to oxygenating or creating a random flow in the tank.
    Maybe what I want to create is impossible without moving parts? I know very little about hydrodynamics and though there may be some way of creating what I want without moving parts
     
  11. PAR
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    PAR Yacht Designer/Builder

    A wing will create a relatively smooth flow from the pipe, vortex generation may be an answer, which can be done with alternating vane angles, though I doubt it would pulse.. It would be very easy with a flap, that would progressively open and close with pressure differentials (spring loaded or counter balanced).
     
  12. viking north
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    viking north VINLAND

    Check out the set up in a live bait well. I'm not familiar with it as i have never had a need to. I don't think your idea of placing a foil inside the pipe to create a vortex will work. In order to create the vortex the flow has to see a high and low pressure area on opposite sides of the foil. On a boats foil keel (or an aircrafts wing) this is created by an angle of attack wqhich in turn generates the pressure differences. The flow then travells aft, down, and around the bottom of the keel attempting to equalize the pressure of the two sides.(likewise on the wing tips of an aircraft) This in turn creates the flow vortex travelling aft. off the bottom end of the keel foil.
    Just had an idea -- wonder what would happen if you tapped in a snorkle hose say at a 45deg. or more angle about three feet or so back from the end of the pipe. The water flow thru the pipe should cause a suction at the 45deg. tap tee thus in effect causing air injection and turbalance into the flow without any moving parts. ----Geo.
     
    Last edited: Oct 19, 2012
  13. daiquiri
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    daiquiri Engineering and Design

    I think there is a misunderstanding here, perhaps due to wrong usage of terminology.
    Turbulent flow is a random flow, and that's ok. But pulsating flow is not random, it is a flow with periodic variations. And then there are waves, which may be intended as a feature of the air-water interface, or as a wave-like motion of a fluid far from the said interface.

    Now, which one of these flow types is the one you'd like to create?
     
  14. daiquiri
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    daiquiri Engineering and Design

    Yes, that's what happens in commercial filter-aerators for fish aquariums, like this one: http://www.amazon.co.uk/Pike-Fishing-Fish-Aquarium-Aerator/dp/B004TL07XG
     

  15. tspeer
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    tspeer Senior Member

    Yes, the trailing vortices behind a lifting surface are due to the surface having a finite span, and will occur in water as well as air.

    I suggest you look into vortex generators. These are small low aspect ratio wings that are mounted to a surface to trail a vortex for improved mixing of the boundary layer.

    Vortex generators come in many shapes. Some are rectangular in planform, some triangular (like a delta wing), and some wishbone-shaped. You can mount them parallel to each other (co-rotating) or at an alternating angle to the flow (contra-rotating). The vortex generators are usually mounted at an angle to the flow that is on the order of 20 - 30 deg. There's a vast amount of literature on the subject, so you can probably find some data that would be relevant to your application.

    The height of the vortex generators will depend on your objective in exit flow from the pump. The larger they are, the higher the losses will be, of course. If you used co-rotating vortex generators arrayed around the inside of the exit pipe, they would impart a swirl to the flow. That may not be what you intend.

    If you are seeking to delay separation at a bend in the pipe or affect the secondary flows associated with a bend, you might want to look at small contra-rotating vortex generators on just the part of the pipe upstream of the inside of the bend, perhaps one diameter upstream.
     
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