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Why is the curvature of pump rotor blades "backwards"?
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Berni:
Yes that is my point that in the special case of having fairly constant pressure everywhere air can act very similar to a fluid. Otherwise do have to treat it as a compressible gas rather than just a fluid. If you move supersonic trough air then you once again need to treat it differently, a wing will act very differently past the speed of sound. Then with water if you move it vigorously enough it will cavitate and again no longer act like a regular fluid.

Lots of models have special edge cases like this, but this does not make them completely wrong or useless, they just need to be used within the limits.

As for density for that i mean the 1.2kg/m3 that the air weighs at sea level versus the 1000kg/m3 density of water. This has nothing to do with being compressible. Plain simple something heavier needs more centripetal force to go around at the same speed, that force over an area is pressure and this is what a centrifugal pump is producing. This is why a centrifugal fan can't pump water and a centrifugal pump can't pump air.
RJSV:
Uhh: Ianb, thanks, let's see if I can repeat your thoughts, that an upwards 'hump' is also going to cause air deflection away, which is up. SO, that looks like the case like you said, that BOTH surfaces actually send an air deflection, away from wing volume, so upside down has similar action.
  BUT, and here is the struggle, I still am perceiving a mention of the principal, if you throw an 'anvil', wearing dollar skates, you move, opposite direction, (due to conservation of momentum).
Do that just means, the upper hump shape will get some DOWNWARD FORCE, a little bit. Why can't I say ' You would crash...downward force could exceed the upward force (supposedly caused by reaction to sending some air downward).
Difficult for understanding.
beanflying:

--- Quote from: Berni on October 15, 2021, 11:51:58 am ---Yes that is my point that in the special case of having fairly constant pressure everywhere air can act very similar to a fluid. Otherwise do have to treat it as a compressible gas rather than just a fluid. If you move supersonic trough air then you once again need to treat it differently, a wing will act very differently past the speed of sound. Then with water if you move it vigorously enough it will cavitate and again no longer act like a regular fluid.

Lots of models have special edge cases like this, but this does not make them completely wrong or useless, they just need to be used within the limits.

As for density for that i mean the 1.2kg/m3 that the air weighs at sea level versus the 1000kg/m3 density of water. This has nothing to do with being compressible. Plain simple something heavier needs more centripetal force to go around at the same speed, that force over an area is pressure and this is what a centrifugal pump is producing. This is why a centrifugal fan can't pump water and a centrifugal pump can't pump air.

--- End quote ---

Stop claiming 'special case' and just use Water or whatever fluid is required and don't muddy the WATER further and drag in supersonic flow. Air is a compressible GAS period full stop. It is NOTHING like an incompressible liquid!
IanB:

--- Quote from: RJHayward on October 15, 2021, 06:17:37 pm ---Uhh: Ianb, thanks, let's see if I can repeat your thoughts, that an upwards 'hump' is also going to cause air deflection away, which is up. SO, that looks like the case like you said, that BOTH surfaces actually send an air deflection, away from wing volume, so upside down has similar action.
  BUT, and here is the struggle, I still am perceiving a mention of the principal, if you throw an 'anvil', wearing dollar skates, you move, opposite direction, (due to conservation of momentum).
Do that just means, the upper hump shape will get some DOWNWARD FORCE, a little bit. Why can't I say ' You would crash...downward force could exceed the upward force (supposedly caused by reaction to sending some air downward).
Difficult for understanding.

--- End quote ---

Just pick the important points out of what you said here. If you throw an anvil away from you while wearing skates, you move in the opposite direction, due to conservation of momentum.

Now apply this same thought to a wing on an airplane. The wing "throws" the air downwards, which tries to move the wing upwards by conservation of momentum. Same principle. Now the actual air flow over the wing is complicated, it curves this way and that on its journey, but at the very end, it is moving downwards to some extent.

In reality, aeronautical engineers use advanced computer design tools with CFD and such to design wings. Modern aircraft need to operate with very high efficiency and wing design is a major part of that. But still, the same basic principle of conservation of momentum is always present.
IanB:

--- Quote from: beanflying on October 15, 2021, 11:24:34 pm ---Stop claiming 'special case' and just use Water or whatever fluid is required and don't muddy the WATER further and drag in supersonic flow. Air is a compressible GAS period full stop. It is NOTHING like an incompressible liquid!

--- End quote ---

Berni has been correct in the posts above. You might try stopping to think about it instead of arguing so much?
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