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Questions tagged [fluid-dynamics]

Questions about the characteristics of fluids in motion.

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What is the physical interpretation of the second term in the viscous stress tensor in the Navier-Stokes equations?

I have been searching for this answer for awhile. I've read numerous texts and even watched some lectures online, but often times this is never explained and just given. The viscous stress term in the Navier-Stokes equations looks…
Adam O'Brien
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Estimating whether the flow through a valve or nozzle cavitates

My understanding is that cavitation occurs in the flow of a liquid when the static pressure drops below the vapor pressure, even intermittently. So even if the time-averaged static pressure (what you might measure) is above the vapor pressure, the…
Ben Trettel
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Which turbulence models are suitable for CFD analysis on a streamlined vehicle body?

Many commercial and open-source CFD codes implement several closure methods for the non-linear convective acceleration term of the Reynolds-averaged Navier-Stokes (RANS) equations. Common methods (also known as turbulence models)…
Paul Gessler
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How to prevent deposition of dust on ceiling fan blades

It is well known that dust gets deposited on a rotating ceiling fan because formation of a boundary layer over fan blades. The air layer next to blade surface is stagnant due to no-slip condition and the presence of a strong viscous force. How could…
Debanshu Thakur
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How are wind tunnel models used when designing supersonic aircraft?

There are two things involved: wave drag and boundary layer separation. The wave drag depends on the Mach number while the latter depends on the Reynolds number of the flow. It's easy to maintain the incoming Mach number as it is independent of the…
Subodh
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How is gas flow through (extremely long) pipelines monitored and controlled?

(This is closely linked with measuring the Mach number inside a nozzle but it is not regarding the supersonic flow) Friction and heat transfer have effects on the Mach number of the compressible flow (Fanno and Rayleigh flow). As it is extremely…
Subodh
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Scale models of thermal plumes

I want to look at the thermal heat plume of a human in still air in a room. So I have a tank of water with a heating coil/cylinder in it. How do I calculate what the heat output of my heating coil will need to be in order to mimic that of a human's…
HCAI
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Contours of radial-flow impeller vane

I've been studying the design of turbopumps and their impellers, all the design equations and what-not; this question concerns the contours of the impeller vanes. I'm going to attempt to enter aerospace engineering in the future, so I figured I…
ecfedele
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Force required to empty a syringe

How would you go about solving the following problem. I believe Bernoulli's equation needs to be employed, but I'm not sure how. Find the magnitude of the force that needs to be applied to a piston of a 20ml syringe with 1cm diameter tube to drain…
thelastpanda
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How is fuel mixed with air in a jet engine?

I am working on an idea that involves a jet engine, but I don't quite know how the fuel system works. In a combustion engine like that in a car, you have nozzles that spray the fuel into the piston chambers (I think, correct me if I am mistaken),…
cluemein
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How to size a heat exchanger for a shear thinning fluid?

To size a heat exchanger, I need to know (among other things) the Reynolds number (Re) as an indication of the flow conditions. The Re number depends on the viscosity. In a shear thinning fluid, I can't assume a constant viscosity, instead it will…
mart
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Is it possible to fire a ball of water that holds its shape?

Background I participate every year in a huge water balloon battle. The clash happens between two universities so you can imagine that the commitment, at least for some people, is quite high. To give you an idea last year some 40000 (thats 40e3)…
Vladimir Cravero
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What drives the honey dipper design?

Honey dippers are often made of wood. Is there a property of honey that drives this? Honey dippers are shaped like ovoids with lateral grooves. Is there something about the viscosity of honey that caused this decision? Is this design somehow…
Jellicle
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Could adding extra engines to AMELIA disrupt airflow from the other engines?

AMELIA is the product of a partnership between NASA and the California Polytechnic State University. One of its innovations is circulation control. An engine is mounted over each wing, and high pressure air is redirected from the exhaust over the…
HDE 226868
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For a small valve in a fluid system, what is the relationship between pressure and flow rate?

The specific example I have in mind is a car tire with a small leak in it. As the pressure increases, does the outflow of air increase linearly, i.e. $v\propto P$, or does it have some more interesting behavior?
Chris Mueller
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