# Tagged Questions

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

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### Sound wave dissipation near a solid body

In this answer to a Physics.SE question I found the following intriguing comment: Under typical conditions the sound absorption length is quite long, and not that much heat is produced. A more ...
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### Can more than one vortex form around a bathtub drain and what determines position?

I don't think I have ever seen more than one "vortex" or whatever you call the tornado-like helical thing that forms when water is draining from a tub. Is the position a function of the shape of the ...
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### Wind Flow Simuation Equation

I have a data that contains pressure measurements in difference locations. Now i want to do wind flow simulation based on the pressure difference between these places. The problem is i want to do this ...
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I am studying a 2D flow and I have a resource telling me that the following holds true for streamlines in general. Let $f$ be the density of the flow, and suppose there exists a unique streamline ...
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### Equal transit time fallacy and Newton's laws of motion

I've seen the equal transit time theory being used to explain aerodynamic lift [basis is Bernoulli's principle] several times. However recently I've been told that there is NO physical compulsion for ...
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### Isothermal compression

What happens when you have gas on a channel with volume V* and p* at atmospheric pressure in an isothermal process and then at time t=0 water acting as a piston is used with a rapid change in pressure ...
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### Scalar form equations for Non-Newtonian fluid

I am having trouble to write down the scalar form equations for this special class of non-Newtonian fluid (Oldroyd-B fluid), I really appreciate your input.
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### What is the velocity in the Navier-Stokes equation?

I have been looking at the Navier-Stokes equation, and can't seem to find anywhere a clear description of what velocity it represents. From what I have read it could be any of the following: The '...
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### Why does viscosity effect the normal component of stress in a Newtonian fluid?

The constitutive law for a Newtonian fluid is $$\boldsymbol{\tau} = 2\mu \mathbf{D} + \lambda\left(\nabla\cdot\mathbf{v}\right)\mathbf{I}$$ where $\mu$ is the dynamic viscosity. Assuming we have a ...
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### Pressure just before the hole in a draining tank

I get extremely confused in fluid dynamics problem where the pressure in some points is required. Consider the ideal fluid in the tank in the following picture. I would like to understand what is the ...
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### Why does laminar flow turn turbulent(*) in external fluid flow and why doesn't a fully developed laminar flow turn turbulent in flow through pipes?

(*:with increase in distance from the leading edge.) I would appreciate if you give detailed explanation for the first question and then apply the same logic to answer the second.
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### Modelling a flow due to an oscillating hemisphere?

Say I have a long cylinder filled with air, closed at one end and open at the other. Now say I place a compressible hemisphere at the closed end and make it oscillate (compression and expansion of the ...
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### Can I recirculate water from an open reservoir to the bottom of a bigger, closed one, without a pump?

A fountain head pumps water out of the main tank into a 'pond' reservoir. Can the water recirculate back into the main tank without the help of another pump? I'm sorry if this a dumb question. I'm ...
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### Prevention of fluid vortex formation

I've been looking for a way to prevent Vortex (whirlpool) formation in a pressurized vessel as it drains, but I am not having any luck finding the parameters at which vortex formation occurs. Is there ...
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### Different locations of a pump in a tube

I'm confused about pumps in fluid dynamics. As far as I understand, the basic effect of a pump which deliver a power $\mathcal{P}$ can be described with modified bernoulli equation between a point $A$...
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### Buoyancy and natural convection in a stratified water tank

I'm working on a simple calculation-model for a hot-water-storage. At the moment I'm stuck on implementing natural convection. To calculate the temperature I've implemented a simple 1D-model in ...
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### Is the system derivative for mass, in the Reynolds transport theorem for mass, always zero?

The Reynolds transport theorem for mass is $$\frac{dm_{sys}}{dt} = \frac{dm_{cv}}{dt} - \dot{m_{in}} + \dot{m_{out}}$$ My question is the term $\frac{dm_{sys}}{dt}$ always zero. Since this is the ...
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### How cold air is less dense in one case and more dense in another case when compared with warm air?

There are two different and contradicting explanations given. Which one is correct? Explanation 1: Cold air is more denser than hot air because ,when cold air of some density, say 'd' is heated, the ...
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### Attractive force between hose and floor when a pool is filled

I was filling a rubber pool for my baby using a hose. But I noticed that if I put the hose outlet directly with the floor there is an attractive force! This is strange, because the hose is throwing ...
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### How to make an equal flow rate in 4 glass tubes with different inner diameters?

I would like to ask a question regarding a flow rate project I've been working on that required pneumatic software to solve. Unfortunately, I don't have the software, and I don't know how to control ...
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### History of Turbulence suggestions

I am looking for extensive historical accounts of turbulence that ideally is strong in math and physics (at least giving references). Any suggestions? The only book I found is "A Voyage Through ...
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### What happens to the flow rate when a water pump is pumping water through a tube that changes size

I'm going to apologize in advance if this is a rudimentary question. It's been 20 years since I took a fluid mechanics class. We are building a waterfall in my backyard. The water pump has a head ...
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### If the pressure between the cross-sections of a pipe is equal, will $P_1$ and $P_2$ be cancelled out of Bernoulli's Equation?

a). Water is flowing through a pipe of two circular cross- sections area $A_1$ and $A_2$ lying horizontally as shown in figure below. The pressure difference between the cross-section $A_1$ and $A_2$ ...
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### why do microscopic cracks happen?

2 weeks ago i asked a question about " Gas permeation through solid metal? " i have got a very good answer here .but microscopic crack was mentioned in the answer. i searched in Internet but i didnt ...