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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).

1203 questions
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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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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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Choosing of repeating variables in Buckingham's Pi theorem

What are the criteria for choosing repeating variables in Buckingham's Pi theorem in dimensional analysis? In many problems, it's solved by taking D,V,H (Diameter, Velocity, Height) as repeating variables. Why do they take the above variables as…
salih kallai
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Does opening a tap in a sink affect the radial speed of the water around the jet?

Does the speed of the water flowing radially outwards from a water jet impacting a sink depend on how far the tap is opened? At the moment, I understand that the maximum velocity of the water in the vertical jet is constant regardless of how far the…
MadCommy
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Bond number for accelerating flow

The Bond number is a dimensionless number typically used to analyze cases where two fluids of different densities are in contact and subject to gravity only. I'm analyzing a system where gas and liquid are entrained in a pipe (think garden hose…
Carlton
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Fluid mechanics cauchy's stress tensor

Is cauchy's stress tensor symmetric always?Does this symmetricity hold in accelerating and non-zero cross velocity gradient flow field?
Mohit Saini
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Flow through flattened tube

Is there an analytical solution for the Navier Stokes equation for flow through a flattened tube ( flat plate in the center and semicircular lobes at the end).
fluid_123
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Formula to describe flow over thin weir

I have thin weir, really just a sheet of metal with a smooth and straight upper edge. I want to know how much water will flow over this weir, when the water level on the higher side is a few cm above the edge. I'm interested in the special case when…
mart
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How to size a fan for open air application?

Assume that you have an axial fan placed in open air with no duct. How can I go about calculating the air speed at a distance x from the fan? The fan is about 1 m above the ground in an open space. I want to use the fan to generate power from a wind…
e.hassouny
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How to calculate the force that a liquid creates on the wall of an underground reservoir

I would like to calculate the force exerted on the wall of an underground reservoir. The volume of rocks surrounding the reservoir creates a force equal to the product of the density of the lithosphere, the gravitational acceleration and the height…
Boris
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Was Isaac Newton's solution to the problem of solid of least resistance comfirmed in space programs?

I was very surprised when i found out that Newton's solution to the problem of solid of minimal resistance was a body with somewhat strange nose cone - the end of the nose cone is a plane perpendicular to the body's axis. So my question is, was…
user2554
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Increase static pressure

I have an application (a tube with parts in it) which needs a certain static pressure in it in order to contain a sustainable air flow. Unfortunately the fan I wanted to use in a push-configuration is not able to create this pressure. Thus I thought…
arc_lupus
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Aerodynamic Turbocharger Design

Looking at the turbocharger picture below there is a compressor and a turbine side. If you dont know the flow direction of the fluid, how can you distinguish which side is the compressor and which is the turbine? Normally for subsonic design this…
Stefan
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