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

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

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

(OP)
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.

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

(OP)
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

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

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?

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

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

(OP)
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.

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

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.

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

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

Mike Halloran
Pembroke Pines, FL, USA

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