can some of the same principles from air be applied to fluid dynamics?

[allblowdup]

Trying to move water through a curved and angled tube at 100+ mph and I have a pinch point part way down. Can I put a slite curve in the sides to help eliminate this? Much like how the fueselage is narrowed at the winng attachment point in an airplane to decrease drag.

 

[KENAT]

Are you referring to area rule/coke bottle fuselage?

That trick helps with compressible flow at transonic speeds.

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[allblowdup]

Yes that is what I was referring to. Although I can't compress the water I thought it could help by allowing the water a larger cross section in that area

 

[GregLocock]

Can you draw a diagram of what you are trying to do?

Cheers

Greg Locock


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[KENAT]

I'll second Greg's suggestion. If you can increase the cross section at a pinch point surely it's no longer a pinch point - so I'm having trouble envisioning what you're saying.

Do you just mean you want to eliminate a sharp 'step' and put a smooth change of cross section instead?

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[allblowdup]

I can post a pic tomorrow but no it's not a sharp step it is a rectangle tube that changes to a round tube that has a curve in it plus a shaft that enters to drive the impeller of the pump. The water is pressure feed at 60 psi to the impeller. The curve and physical limitations make a tighter cross section in one area. The problem with water is that it begins to act like a solid at speed and pressure. I want to barrel out the sides a small amount but am concerned that 1. The water will not actually flow in there and I may be no further ahead or 2. It may cause turbulence enough to hurt the efficiency of the design.

 

[3DDave]

You'll be making a convergent/divergent nozzle. If it is done right there will be low loss in the fluid. Water is still a fluid, just one of the least compressible ones.

It may be hard to get general information. In gas flow the most interest lies in the formation of a shock wave within the nozzle, a result of compressibility - which water doesn't have much of. In typical liquids the use of a convergent nozzle is to accelerate the fluid to become a free jet in air or an unstable stream that atomizes the fluid into small droplets.

You may wish to view some of the material here:

http://web.mit.edu/hml/ncfmf.html

particularly Fundamentals-Boundary Layers which covers divergent nozzles. The presentation on Cavitation also may be applicable as you are using an impeller.

 

[MikeHalloran]

It sounds like you're trying to homebrew a waterjet pump.
Go and look at some regardless.


Mike Halloran
Pembroke Pines, FL, USA

 

[allblowdup]

here is a 2d image of what i have so far. This is about as good as I can get it. another question would be if there is anything to be gained by trying to increase the boundary layer by machining grooves in the roof of the pump?

 

[allblowdup]

Here is a pic of the pump as it is now.

 

[allblowdup]

One more.