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

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Maximum hole size to stop a fluid passing through a solid

In a previous question, the following is answered in a general sense: Assume I have a inverse cone which holds 200ml water. I am going to cut the tip of the cone to create a small hole. How to ...
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0answers
57 views

Meaning of a Dirac delta speed in 1d shallow-water equations

A 1d thin layer of a fluid of constant density in hydrostatic balance can be modeled by shallow-water equations: $$\begin{align*}\partial_tu+\partial_x\left(v+\frac{u^2}{2}\right)&=0,\\ \...
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1answer
38 views

The relationship between height of water and the rotational speed inside a cup

When I stir the water inside a cup with a speed $v$ ( using a stick), I find that a vortex will be formed inside the cup, with the middle part of the water at the lowest point ( with the height $h_0$),...
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0answers
25 views

What are the dynamics of the “break the surface tension with a drop of soap” experiment?

There's a common experiment exemplified in the first few seconds of this video: https://www.youtube.com/watch?v=WsksFbFZeeU You put some food coloring in the center of a plate of milk, then put a ...
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0answers
28 views

Why is the velocity of fluid on top a hydrofoil higher than that on the bottom? What keeps enlarging the difference in these 2 velocities?

I am trying to learn how hydrofoil works. A big part of it is Bernoulli's principles. I found this article on MIT website. There are two explanation for how it works: The conservation of linear ...
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61 views

Are tides just very very very weak spaghettification?

I was wondering as to why there are two tidal bulges instead of just one on Earth, and then I saw this diagram: The oval shape that the Earth's water is transformed into in this image reminded me of ...
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79 views

The Madelung Equations are Euler Equations for Quantum Mechanics. What is the Lagrangian description of Quantum Hydrodynamics?

The Madelung Equations of Quantum Mechanics suggest the Hydrodynamic Model of Quantum Mechanics (Quantum Mechanics is described as a fluid of universes in a multiverse, which, in the non-relativistic ...
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1answer
90 views

Gas permeation through solid metal?

if i make a box from aluminum ( 0,5 mm thickness ) and put air in it ( about 2 bar or 3 bar). would the box lose the air over time (10 years period) or not ? assuming the temperature will change ...
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35 views

Is it possible that propagation of acustic waves leads to emission of radiation?

Question: Consider large cloud of gas. Assume it is electrically neutral (but as always, matter is composed of smaller things which are actually charged). Is it possible that propagation of sound ...
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1answer
27 views

How can I determine the height in this fluid dynamics problem? [closed]

Here's the problem: I used Bernoulli's Equation and tried to make the height the subject: The tricky thing about the problem is that the initial height is not given. Checking by dimensional analysis ...
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1answer
31 views

As hot air rises is the cold air that rushes in pushed in or sucked in?

I seem to remember from high school, the state of equilibrium. Volumes of more molecules wanting to get to a volume of less molecules and causing a state of equilibrium. From this I believe cold air ...
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429 views

How do I enforce the no-slip boundary condition in time dependent incompressible pipe flow?

This is a technical problem which must have been solved already. It won't be in beginners textbooks but there should be a solution somewhere. I welcome reading suggestions. Maybe someone with ...
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40 views

How are boundary consitions implemented correctly in time dependent hydrodynamics?

I posted this question more than one year ago and got an answer recently. This answer looks good to me, but indicates that something is wrong in my original approach to the problem. Can someone tell ...
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7answers
6k views

Supergun Launching of Satellites

I should say first that I don't believe this is a feasible launch method, otherwise NASA and other space agencies would be using it by now. It's based on this BBC news story Saddam Hussein's Supergun ...
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1answer
46 views

Physical reason of adding salt when we're cooking rice (osmosis)

Why do we add salt when we're cooking rice? I know one reason is related to the boiling point of water but someone said it is also related to "Osmosis". What is the relation between adding salt and ...
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1answer
4k views

Does water turn solid under deep ocean because of high pressure?

I know that we can make water solid with high pressure, so I think water will be solid in the deep ocean? If that is true, the depth of the ocean would be limited because water will become ice? ...
2
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1answer
276 views

Maxwell-Boltzmann distribution for transport equations

I have to calculate the transport coefficients for the Maxwell-Boltzmann distribution. But I'm not sure what distribution I have to use. As far as I know it should not be the MB distribution for $v$-...
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1answer
28 views

Systematic+Random Uncertainty for velocity measurement

I have a question regarding systematic and random uncertainties. I have to measure the mean value of a velocity measurement in flow field at a point. I've recorded say 1000 samples in time, which I ...
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26 views

How do I compute mass flow rate for a compressible fluid?

Consider the vacuum chamber in the figure. If a hole with cross section area $A_{cs}$ is created, how can I approximate the maximum mass flow rate, $\dot{m}$, for a compressible fluid (e.g. air)?
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24 views

Ratio of Stagnation to Normal Flow Properties in Incompressible Flows

I know in compressible flows the ratio of stagnation to normal flow variables is a function of the Mach number and usually the specific heat ratio. Does this ratio mean anything for incompressible ...
6
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2answers
177 views

How do we explain the existence of liquids, from a mathematical or computational perspective? [closed]

This post asks why matter exists in three phases. Most of its answers explain the existence of liquids with some variant of the following: liquids happen when thermodynamic conditions, temperature ...
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0answers
32 views

How is zonal flow defined and computed?

The transition to turbulence in pipe flow was recently observed to be in the same universality class as directed percolation. This was done by reinterpreting the turbulence and laminar flow in terms ...
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1answer
59 views

Power generation with a long, horizontal pipe, using atmospheric pressure differences

Straight to the point. If I float a pipe starting from a point in the ocean that has the atmospheric pressure of 101 kPa (Call it Point A) all the way to another geographic position on the ocean with ...
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6answers
494 views

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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1answer
633 views

Solve unsteady state Bernoulli equation for flow in a pipe

I am an engineer studying an unsteady-state flow through a pipe. The Pipeline has been cleanly cut into two halves, without deforming the cylindrical form of the pipe, exposing the contents to ...
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0answers
63 views

Mass of star from Lane-Emden equation

Suppose we have equation of state $p=K\rho^{1+\frac{1}{n}},$ where $\gamma=1+\frac{1}{n}$ for some star. Then by standard calculations we obtain equation for enthalpy $h$: $$\Delta h+4\pi G\left(\frac{...
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1answer
78 views

How to derive end-correction value relationship for open-ended air columns?

According to Young and Freedman's Physics textbook, in open-ended air columns like some woodwind instruments, the position of the displacement antinode extends a tiny amount beyond the end of the ...
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0answers
21 views

What is vortex row image system in fluid mechanics?

What is vortex row image system in fluid mechanics? I have lot search but I did not find any best answer about this question. Please explain about this topic or give me best link of book or site.
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2answers
49 views

Application of Bernoulli's equation to siphon

I'm trying to understand how to use Bernoulli's equation in practice. So I will make an example of where is my confusion. I found this great explanation on Wikipedia about the siphon, but there is a ...
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2answers
57 views

Analysis of a system consisting of a leaking tank of water

The departure point is this problem: A water tank on wheels is moving over an horizontal trail with negligible friction. There is a small opening in one of the walls, at a depth of $h$ below the tank'...
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1answer
210 views

Smoothed particle hydrodynamics in cosmological N-body simulations

What is the role of smoothed particle hydrodynamics (SPH) in cosmological N-body simulations like the Millenium Run (performed with Gadget-2)?
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1answer
638 views

Lorentz force for electrically conducting fluid flow in homogeneous magnetic field

I am mathematician and have paper which models situation when homogeneous magnetic field is applied to moving electrically conducting fluid. There is such Lorentz force formula on which all the work ...
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1answer
70 views

Raising a cut on your arm above your heart

I often read that when you have a deep cut on your arm, you should raise your arm to the point where the cut is above your heart. This should reduce the amount of blood loss because less blood reaches ...
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1answer
48 views

How could water pour out from upside-down bottle, unless its pressure is smaller than atmosphere pressure?

Just a simple question : when we remove a stopper of an upside-down bottle, water flows out. But the pressure caused by the mass of water's column is usually smaller than atmosphere pressure unless we ...
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26 views

What is the relative velocity term in drag and lift force in the following case?

When a stationary particle is introduced in a fluid moving with horizontal velocity $V_fx$, what is the relative velocity terms in the drag force ($F_D$) and lift force ($F_L$) equations. Am I correct ...
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2answers
367 views

The demise of the Tacoma Narrows bridge was casused by aeroelastic flutter. But isn't that just a special case of resonance?

Much of the research I've done on the Tacoma Narrows bridge disaster of 1940 attribute the collapse of the bridge due to aeroelastic flutter - not strucural resonance. But isn't aeroelastic flutter ...
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1answer
48 views

Why does stagnation pressure reduce across a normal shock?

I am seeking an explanation for this graph where the subscript "1" refers to the supersonic region and the subscript "2" refers to the subsonic region present beyond a normal shock. The static ...
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65 views

What is the variation of pressure in rotating fluids(in accordance to the question in the image)? [closed]

This is an interesting question that I came across. Please see attachment. It is a multiple answer type question. My answer was B and D. I have attached my derivation for this problem. I want to know ...
5
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1answer
86 views

If a high speed car or train enters a tunnel, will the aerodynamics effect slow it down and hence requiring more energy to maintain speed?

Speed and distance are two main determinants in this question. A slow moving vehicle or train entering a tunnel is unlikely to be affected by the presence of solid stationery object covering them. But ...
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1answer
39 views

What amount of force could be created by a person “swimming” in air?

Had a question on a physics test, a person is at rest on a frictionless surface and can not throw anything, can they move? I said yes, by "swimming" against the air and got docked because "it wouldn'...
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1answer
39 views

When does $ S\cdot v=\mathrm{cost}$ hold?

In fluids dynamics what are the limitations for the use of the volume flow rate conservation law? $$ S\cdot v=\mathrm{cost}$$ Does it still hold when there are external forces acting on the system, e....
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1answer
54 views

What is the direction of buoyancy in the bulk of liquid on earth?

I have a trouble when considering the direction of buoyancy in the bulk of liquid subjected to vertical temperature gradient. The liquid is heated from below or above that induces a natural convection ...
4
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1answer
92 views

Why do I spill lesser water if it's hotter?

If I pour water in a glass to make a cup of tea, I noticed that if the water that comes out of the kettle is very hot, almost no water is spilled. If the water is cold though, much more water is ...
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What about negative Pressure?

Here is something I see : Let's say the ideal fluid(water here) of density $\rho$ is drawn from a source by a motor and thrown upwards with a velocity $v$. Now we take the power of motor be ...
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448 views

An equivalent for the Bernoulli equation for viscous liquids

I was wondering whether there is any equation for viscous liquids (probably derived from energy and mass conservation principles) relating the pressure, rate of volume flow, area of cross section and ...
3
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1answer
31 views

Inertial Waves - Why neglecting the advecting term?

I'm trying to derive the dispersion relation for Inertial waves. In Cartesian coordinates: Inviscid and incompressible fluid is rotating uniformly with Angular Velocity: $\Omega = (0, 0, \Omega)$ ...
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42 views

The convective term in Reynolds Transport theorem

Reynolds Transport theorem states that $$\frac{D B_{sys}}{Dt}=\frac{\partial B_{CV}}{\partial t}-\dot{B_{in}}+\dot{B_{out}}$$ where $B_{in,t+\Delta t}=b_1m_{1,t+\Delta t}=b_1\rho_{1}\forall_{in,t+\...
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1answer
6k views

How does smoke move in the air and how can I direct it so it will go to a place I want it to go?

Let's assume a close room with 1-2 people who only one of them smoking cigarette. What is the equation describe the smoking spreading? is it diffusion? what are the parameters is so? Is there a way/...
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2answers
168 views

Nomenclature clarification concerning solitons

My experience with solitons is restricted to the classical setting, namely solutions to the quartic interaction $\phi^4$, the Sine-Gordon equation, and Korteweg–de Vries equations. I was explicit to ...
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1answer
1k views

Best way to move teaspoon to dissolve sugar in a cup of tea

I know that there is asked questions about something like cooling down cope of coffee..etc, but this one is little different. My friend was watching TV program of English eating etiquette, and they ...