Rotating Shaft Advise: Solving Problem at Sea Level

In summary, the conversation revolves around the question of whether the rotation of a 280mm shaft at 3000 RPM can create enough resistance to prevent air from flowing between two separate environments with different pressure ratios. The person seeking help is unsure of how to approach this problem as they have no experience with rotating equipment. Possible solutions mentioned include using a seal or measuring the windage off the shaft, but it is noted that the 10mm gap between the shaft and plate is a potential issue. The conversation ends with a suggestion to consult a technical memorandum from NASA or to measure the windage in order to find a solution.
  • #1
revgrad
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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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  • #2
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.
 
  • #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 separate environments? Or do I assume the gap only because the spinning shaft has no bearing on my problem.
 
  • #4
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.
 
  • #5
Thanx for the help and info.
 
  • #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:
 
  • #7
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.
 

1. What is a rotating shaft?

A rotating shaft is a mechanical component that is used to transfer power and motion between different parts of a machine. It typically consists of a long, cylindrical rod or bar that rotates around its own axis.

2. How can a rotating shaft cause problems at sea level?

At sea level, the air pressure is higher than at higher altitudes, which can create a greater load on the rotating shaft. This increased pressure can lead to higher friction and wear on the shaft, causing it to overheat and potentially fail.

3. What are some common problems that can occur with rotating shafts at sea level?

Some common problems with rotating shafts at sea level include overheating, excessive wear and tear, and misalignment. This can result in decreased efficiency, increased maintenance costs, and even equipment failure.

4. How can these problems be solved?

To solve these problems, it is important to properly design and maintain the rotating shaft. This includes regular lubrication, proper alignment, and using materials that can withstand the higher air pressure at sea level. Additionally, regularly monitoring the shaft's performance and addressing any issues promptly can help prevent larger problems from occurring.

5. Are there any alternative solutions to rotating shafts for transferring power and motion?

Yes, there are alternative solutions such as using gearboxes, belts, or chains to transfer power and motion. However, rotating shafts are still commonly used due to their simplicity and efficiency. It is important to carefully consider the specific needs and requirements of a machine before choosing an alternative solution to a rotating shaft.

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