Golf Ball Fluid Dynamics

Discussion in 'Boat Design' started by Inquisitor, Nov 28, 2005.

  1. cyclops
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    cyclops Senior Member

    America is the only country I know of where all the sheep believe anything that has stated, a STUDY was done, on the product or idea. People here take any medicne for a cold with STATED side effects of, seizures, liver failure, stroke, constipation, high blood pressure, severe allergic reactions and in rare cases death. What do Americans have for medical common sense? The same seems to hold true in boating. This is a improvement. Look at our biased charts to prove how good it CAN be. If you belive a little lie, why would not someone tell you a bigger one? I think I am bugged by gullibility.
     
  2. RHough
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    RHough Retro Dude

    You are getting close.
    If there is separation due to a change from laminar to turbulent boundary layer flow,
    if tripping the boundary layer flow from laminar to turbulent before the separation point will keep the flow attached
    if the resulting drag will be reduced more than the increase caused by the force needed to create the turbulent flow:
    then the net drag will be lower.

    If the boundary layer flow at the separation point is already turbulent no amount of extra turbulence will get the flow to re-attach and the total drag will be increased.

    Want to bet that the windshield trim moulding has already tripped the flow to turbulent at the leading edge of the roof and the trip strip at the trailing edge does nothing?
     
  3. kach22i
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    kach22i Architect

    I've skimmed over all nine pages of the PDF's from that dimple website:http://www.lessgasmoremiles.com/

    And they claim to have tested it on many things, propellers, hydrofoil foils and such.

    They claim to have lowered noise.

    They also say that the dimpled surface must be positioned prior to the expected turblance or point of air breaking away - just like RHough said to.

    I'm just keeping an open mind, not buying into anything. Most things in my life I don't understand how they really work, including my computer - yet I use them everyday and they work.
     
  4. RHough
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    RHough Retro Dude

    I don't doubt that for one second. How they can stretch reduced noise to increased fuel economy (less drag) would be interesting reading. :rolleyes:

    Owls fly silently (low noise) but they don't glide well (high drag).

    Maybe the combination of the trip strips, magnets on the fuel lines, and a tornado thingy in the air cleaner will combine to save enough gas so that I have to stop every week and empty the tank?

    Customer, meet B.T. Barnum ... one every minute. :D
     
  5. kach22i
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    kach22i Architect

  6. RHough
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    RHough Retro Dude

    sigh ...

    The dimple tape patent proves that any idiot can get a patent.

    Some of the statements in the patent are just WRONG.

    My favourite is the one where his invention "adds" kinetic energy to the boundary layer ... where does the energy come from?

    His "proof" of concept experiment shows a complete lack of knowledge. He uses a propeller and measures static thrust. Propellers are most inefficient in the static thrust condition, that is not the design point.

    After having "proved" that his static thrust propeller is less inefficient, his logic is that the change in efficiency will extend to the design point. BZZZZZ! Wrong answer.

    The dimple strip cannot "add" energy, it can transfer energy. The total energy of the system is fixed. Energy cannot be "created".

    The "improvement" in off design point performance is paid for by energy transfer to the boundary layer when it is not required. Airfoils DO NOT have separation when operating at their design point.

    There is no free lunch.
     
  7. RHough
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    RHough Retro Dude

  8. kach22i
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    kach22i Architect

    They used all the tin foil to make a bong, I would of thought driving a van alone would of gave that one away.;)
     
  9. FRA2003
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    FRA2003 New Member

    Maybe i can help you a little bit on the subject as a french aerodynamicist.

    First, talking about hull drag minimization, one must know that every surface
    treatment or energy injection that cause a modification of the underwater
    boundary layer is generally forbidden in many sailing rules.
    Ribblets do reduce the frictionnal drag. But their maintenance is expensive because of the wearing effect of friction. I heard a story about a test realized
    by OneAustralia. They prepared the hull with a special anti-fouling. The day after the first training, all the rugosity was smoothed.

    Energy injection in the boundary layer does also reduce the drag. the french
    jetfigther MIRAGE 2000 is equipped by a leading edge suction device that controls the airflow during the landing phase. Some tried to inject petrol in
    the water. It does also work, but i am not sure it is the best way to reduce
    the drag of a boat.

    What is the net gain of such things ? In laboratory, one can find that we
    can reduce the drag by 10%. But in reality ? On the water ? I guess we have so much to do in construction, especially in composite boats, to ensure the
    symmetry of the hull and appendages. We must also take account into the natural turbulence rate of the water, that change a lot from one zone to another. We must not forget to introduce the wave effect on the transition on the boundary layer when designning off-shore boats. God, my whole life will never be enough !
     
  10. kach22i
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    kach22i Architect

    Something struck me yesterday - my other hobby, stereo.

    B&W, Bose and I think Energy all use dimples on their bass ports. They all claim it cuts down on air noise as the woofer pumps in the enclosure.

    Also the thing about air not leaving disruptively on a wing or propeller which is properly designed, neglects to mention stall angles and cross winds all of which distrupt idea situations of air flow.

    Dimples work, the where when and why is not fully understood by all, and this opens a marketing oppurtunity for some, and serious experiments for others.
     
  11. kach22i
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    kach22i Architect

    Thanks for the information, I never knew this.:)

    Note: Early experiments of adding bubbles of air under and along a hull eventually lead to the development of the Hovercraft - my personal watercraft of choice.

    1989 Scat II HP, 35 HP, 30 inch fan, 45 mph over water, land or ice, 2 persons, 10 foot long by six foot wide with six inch clearence height.[​IMG]
     
  12. RHough
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    RHough Retro Dude

    B&W, Bose and I think Energy all use dimples on their bass ports. They all claim it cuts down on air noise as the woofer pumps in the enclosure.

    If a pattern of flow creates waves with amplitude and frequency withing the range of hearing it is sound. That is an objective observation.

    If the sound is unpleasant it is called noise. That is a subjective opinion.

    In audio, objective noise would be sound not generated by the source. Eliminating sound waves not created by the source is one of the design goals.

    Also the thing about air not leaving disruptively on a wing or propeller which is properly designed, neglects to mention stall angles and cross winds all of which distrupt idea situations of air flow.

    I said at the design point, stall condition and yaw angle of attack are not the design point. If a foil section is chosen that suffers from laminar flow separation with no turbulent re-attachment within the design envelope the section was a poor choice. Adding turbulators is one way to avoid having to change the section (cheap fix for design error). The extra drag of the turbulator is paid for with reduced performance at other points in the envelope.

    Dimples work, the where when and why is not fully understood by all, and this opens a marketing oppurtunity for some, and serious experiments for others.

    That turbulators work is nothing new. That dimples work with lower drag penalty than other turbulators is unknown. Nothing in the patent even attempts to measure or evaluate the effect of the dimples under conditions where separation does not occur.

    For example suppose we have a foil section that in normal condition the flow changes from laminar to turbulent at 60% of chord length.
    At some angle of attack the flow separates at 40% of chord.
    We then add turbulence at maximum camber of 30% of chord.
    The turbulence eliminates the separation.

    We now have a foils that has turbulent flow aft of the 30% point rather than aft of the 60% point. We have reduced the low drag laminar flow area by 50% at all angles to gain a reduction in drag at the separation angle.

    This is a net loss.

    Ideally the tabulator should only work when separation is present and not when it is not needed.

    Dimple tape does not retract under normal flow conditions, thus the drag penalty is always present.
     
  13. RHough
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    RHough Retro Dude

    Why would you want to reduce drag during landing? Adding drag and reducing L/D is what landing is.

    The landing phase is high AOA operation at low airspeed. This is a condition that can create flow separation. The flow control during landing is to reduce or eliminate separation so control can be maintained, not to reduce drag.
     
  14. FRA2003
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    FRA2003 New Member

    To mister Rhough.

    Please excuse me if i took some shortcuts to explain the principle of flow control. During the landing phase, wings are trimmed at the maximum because of the reduction of the air speed. It is a very critical phase. To ensure that the wing will not stall, one must control the flow separation zone. As a consequence, keeping the airflow laminar on the wing does also reduce the drag, even if it is not exactly the purpose.
     

  15. FRA2003
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    FRA2003 New Member

    About the design envelop... to mister Rhough

    Can you please tell me what is the design envelop for a rudder of a off-shore racing boat that goes from North Atlantic to North Atlantic via the South Atlantic, the Indian Ocean and the Pacific ? Off an ACC boat in the San Diego's bay. Do we must also take account into the modification of the hull flow when colliding with a dolphin ?
     
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