# Tagged Questions

The quantitative study of how fluids (gases and liquids) move.

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### Why is it easier to remove stains with water?

And I don't mean stain removers, but literally tap water. See here's the thing, you can't remove a stain without some sort of friction, and water reduces friction. Yet if I say, spill some coffee and ...
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### Water Jet scenario [duplicate]

So I have a question I came across that goes along the lines of Water is discharged from a 20 mm diameter nozzle to the atmosphere. The water jet leaves the nozzle with a velocity of 12 m/s and is ...
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### Pressure drop through a flat vs. pleated filter

Consider two identical pipes where two identical air flows take place. The pipes are "obstructed" by two filters made of the same fabric, one flat, the other pleated as shown in the following picture. ...
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### Physical Meaning of Over- / Underdetermined Acoustic Eigenvalue Problem

I am performing an eigenmode study on a system of acoustic ducts. The system consists of two large cylindrical volumes connected by several smaller cylindrical volumes (modeling a combustion chamber ...
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### How do ceiling fans cool or heat?

Why does a ceiling fan blowing air downward cool in the summertime: whereas a ceiling fan sucking air upwards heats in the wintertime: ? Why isn't it the other way around?
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### Three-dimensional centrifugal instability and the Rayleigh critertion

Lord Rayliegh postulated that for a two-dimensional symmetric swirling flow, a three-dimensional instability may occur if the angular momentum magnitude decreases in the radial direction with respect ...
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### Rotational and irrotational flow

Can a rotational flow take place if there is no viscosity? If yes then will it always be rotational or will it become irrotational after some time?
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### How relevant are Reynolds number and flow regime in very small tubing at very low flow rates?

I know that in bigger pipes, Reynolds number and the dominant flow regime can be important in further decisions. Now, I have an application with tubing of about 0.5 mm in diameter and a flow rate of ...
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### Contact Angle In Capillary

One Professor recently told me that in an insufficient length capillary, the contact angle doesn't change, its an inherent property which does not change. If the edges of capillary are extremely sharp ...
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### Rotating droplet of liquid

I'm interested in the fluid dynamics of a spherical droplet of liquid whose surface is forced to rotate at a constant velocity. I'm interested in either steady-state solutions (the internal flow ...
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### How does gas friction emerge?

The fluid parcel model states that a gas can be modelled as the sum of infinitesimal small parcels. According to this model, the friction of a gas with a solid surface (e.g. the wall of a pipe) ...
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### Do gases have phonons?

A phonon is a quantized unit of sound; they are encountered when quantizing lattice vibrations in solids. Now, even an ideal gas supports sound waves, but in such a case, interactions between atoms ...
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### acceleration of water when it travels through garden hose

How to derive average acceleration of water as it travels through nozzle of garden hose. Suggest some assumptions for better understanding
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### Why would oscillation of a gas column inhibit rather than promote mixing?

Many years ago I helped to support an experiment conducted in Japan which investigated the effects of high frequency oscillation ventilation (HFOV) on the mixing and distribution of gas into the lungs....
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### Is there any electric current in a continuous medium of moving charges?

Consider a continuous charged fluid (unlike in real life where charge is carried in discrete chunks like electrons) in a bottle. Suppose that the fluid is stirred in a circular manner and then left to ...
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### Water Moving Through Coffee Grinds

Like many of my peers, I rely on coffee as if it were prescribed to me. It might even be classified as an addiction if it weren't for the cultural norms surrounding a cup of coffee or tea in the ...
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### Pressure required for gas to flow through an orifice

Imagine I have an upside-down cone, which is filled with a gas - let's say it is air. At the bottom of this cone is an extremely small hole (a few microns in diameter). How do I go about calculating ...
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### Effect of wall friction on stagnation pressure and temperature

We have incompressible air flowing through a cylindrical pipe, from section A to section B. The process is considered to be stationary. My theory book says that, because of the frictional losses on ...
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### Intuitive explanation for lower pressure above airfoil

From Bernoulli's principle we know for an incompressible fluid (constant density $\rho$) in a gravitational potential $\psi=gz$, that we can state the equation along a streamline from point 1 to point ...
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### Can drag force and lift force be in the same direction in the following case?

In the attached picture, can I say that there is a lift force in the Y-direction, and a drag force too in the same Y-direction? $F_L$ proportional to $V_fx^2$ ? $F_D$ proportional to $V_py^2$ ? Is ...
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### Is drag force in the direction of particle motion or opposite to motion?

Suppose water is flowing in horizontal direction (positive $x$-direction) and a particle immersed in that water is also moving in the same direction. In this case, is the drag force $F_D$ in the ...
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### Trouble understanding a formula in Turbulence

I'm very new to turbulence.I'm reading this book on "Turbulence: An introduction for scientist and Engineers" by Davidson. I came across this formula for energy dissipation. This is in chapter one. I ...
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### Bent capillary tube

What would happen if I bend a capillary tube and use it as shown in figure? 1.Will the water(or any other adhesive liquid) level remain same as before bending? 2.or it will come up till end? 3.Or ...