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Rotating Shaft Advise

  1. Mar 18, 2008 #1
    I am unsure of where to begin to solve for my problem since I have no experience with rotating equipment. I have a 280mm rotating shaft @3000 RPM running thru a flat plate 45mm thick with a 300mm dianeter opening for the shaft. Being at sea level the one side has air pressure ratio of 1.000 while the other retains a pressure ratio of .8320. Does the rotation of the shaft create enough resistant force to prevent the environment of opposing sides from interacting with each other? Or do I assume there will be leakage fromone side to the other and ignore the forces of the rotating shaft as negligable?
     
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  3. Mar 18, 2008 #2

    FredGarvin

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    Is there some kind of seal in the plate that the shaft goes through? If there is nothing there then of course there will be leakage in the direction of the decreasing pressure.

    What forces of the rotating shaft are you referring? Why would these forces have any impact on the flow rate through the opening. Your description makes me believe that there is no way the shaft can influence anything in that area.
     
  4. Mar 18, 2008 #3
    "...What forces of the rotating shaft are you referring? Why would these forces have any impact on the flow rate through the opening. Your description makes me believe that there is no way the shaft can influence anything in that area."

    The reason I brought up the forces from the shaft is when this large diameter shaft is rotating at 3000RPM there is (you can feel) air being forced away from the spinning surface by the rotational forces. Since there is only a 10mm gap between the shaft and the plate it goes thru, is there enough generated resistance because of this forced air to create a barrier from the two seperate environments? Or do I assume the gap only because the spinning shaft has no bearing on my problem.
     
  5. Mar 18, 2008 #4

    FredGarvin

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    You will have some windage off the shaft, but those flows at only 3000 rpm should be very small. The delta P across your gap would be the more dominant I would think.

    Just be careful with this gap. If your shaft has any imbalance, it will wobble on you. 10mm a side is not much space to take up.
     
  6. Mar 18, 2008 #5
    Thanx for the help and info.
     
  7. Mar 19, 2008 #6
    "You will have some windage off the shaft, but those flows at only 3000 rpm should be very small. The delta P across your gap would be the more dominant I would think.
    Just be careful with this gap. If your shaft has any imbalance, it will wobble on you. 10mm a side is not much space to take up
    ."

    Just curious, how does one approach figuring out the pressure between the rotating shaft and stationary plate? I have never worked in hydrodynamics and haven't a clue of where to begin.:confused:
     
  8. Mar 19, 2008 #7

    FredGarvin

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    The only places I have ever been worried about windage were in high speed situations, an alternator rotor and geraboxes. In those cases we did particular testing to measure the effects. However, Jim Vranik from NASA-Lewis put out a technical memorandum
    NASA TN D-4849. It is a paper covering his method for arriving at windages from high speed alternators. You can give that a try to see if it fits your application. Other than that, the only thing I could recommend is to actually measure it.
     
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