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Questions tagged [fluid-mechanics]

Questions relating to fluids at rest (fluid statics) or the forces and effects of fluids in motion (fluid dynamics).

1073 questions
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Is it possible to "pump" a powder?

Is it possible to "pump" a powder the same way liquids can be pumped? If so, what are the challenges? If not, what are some alternatives?
peterh
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Is it possible to build an air compressor with no moving parts?

Is it physically possible to build an air compressor with no moving parts? I'm envisioning a thermodynamic cycle capable of compressing air with no moving parts and operated in a stationary way. There is no limitation on the compression factor,…
user3368561
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How to know whether the flow is supersonic in a nozzle?

For a project I had built a convergent divergent nozzle designed for Mach number = 3. In that project, I could know the flow has gone supersonic by seeing the manometer fixed between the throat and the divergent section (drop in pressure, as the…
Subodh
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How to stop water flow in a siphon?

I have assembled a small DIY drip-irrigation system for my terrace garden. Please have a look at the attached image. I switch on a small pump to start the drip-irrigation system and then switch it off. But even after that, the water keeps flowing…
javed
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Windmills in empty fields. Why no trees?

I have noticed that windmills are generally built in empty fields with no trees around, and I've been wondering why... A windmill is generally way taller than trees and I can imagine that trees don't actually affect the flow (see picture). But is…
Physther
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17
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2 answers

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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15
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How to calculate flow rate of water through a pipe?

If a water pipe is 15 mm diameter and the water pressure is 3 bar, assuming the pipe is open ended, is it possible to calculate the flow rate or water velocity in the pipe? Most of the calculations I have found appear to need 2 of these: diameter,…
Richard
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5 answers

Purpose of spheres and fins on submarine propeller

On a recently launched Russian diesel-electric submarine, the rear propeller has two distinct features. You can see spheres at the base of every propeller blade: Also, the trailing edge of the shaft has four adjoining fins in line with the axis of…
Rupert Reckless
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14
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3 answers

How to determine the characteristic length in reynolds number calculations in general?

I understand that the reynolds number is given by the expression $Re=\frac{\rho v L}{\mu}$, where $\rho$ is the density, $v$ is the fluid velocity and $\mu$ is the dynamic viscosity. For any given fluid dynamics problem, $\rho$, $v$, and $\mu$ are…
Paul
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Why is Mach 0.3 the threshold separating compressible and incompressible flow?

I've read that Mach 0.3 is pretty much the upper limit for treating air as an incompressible fluid. The sources I've read seem to treat this as a given, without proof or justification. Why is this the limit? Is there a mathematical justification…
Paul
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13
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How do the bubble oscillations in two-phase flows affect the dissipation rate of turbulent kinetic energy?

I am investigating the effects of bubble oscillations (calculated using the Rayleigh-Plesset equation for bubble dynamics) on the turbulence in two-phase flows. Since I am using cryogenic fluids, the thermal effects also play a role. I am trying to…
Karthik Venkatesh
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13
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3 answers

What makes the material travel through Archimedes' Screw?

...or in other words, why doesn't the material just stick to the screw, rotating in place, without progressing along its length? In the simplest case, the answer is obvious: gravity. If it's a granular or liquid material and the screw is tilted to a…
SF.
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What is the meaning of vorticity and circulation?

In fluid kinematics I can't understand the meaning of these terms : vorticity and circulation. Can somebody give me a description of these terms so that a lay person can understand them easily?
M.Tarun
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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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Low cost, moderately accurate water depth measurement

tl;dr: After an extended conversation with an old-timer, I realized a few things: The single most valuable measurement for the majority of people will be water-depth-in-well. The second most valuable will be water-flow-from-well. The "bubbler"…
Peter Rowell
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