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

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How does this help an aeroplane to fly? [duplicate]

I read it somewhere on the internet that wings of an aeroplane are designed in such a way, that they increase the velocity of air above the wings and so pressure above the plane becomes less than the ...
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1answer
210 views

Sailing against the wind. Is this a fair model?

I was ruminating the explanations about how boats can sail against the wind (or "into the wind"), and wondered if one could devise a simple mechanical model without hydrodynamics involved. Imagine a ...
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1answer
106 views

Non-determinitric flow of water stream on vertical porcelain surface

I noticed several times while washing my hands that accumulated water when starts streaming vertically does not flow vertically in straight line on vertical porcelain surface under the force of ...
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2answers
667 views

Efflux speed of ideal fluid dependent on diameter?

I have a cylinder full of water with diameter $D$ with a round opening on the bottom with diameter $d$. The water is friction-free and incompressible. Now I need a relationship for the efflux speed ...
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1answer
120 views

Blimp challenge. Doubts about volume at different heights [closed]

I want to design and build a small semi-rigid airship/dirigible. It will be controlled with RC so I will install motors, arduino, battery etc. Filled with helium. Weight of the equipment is about 2kg ...
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3answers
187 views

Explain Turbulence [closed]

I'm a high school student. I still don't understand what turbulence is. Please can you explain what it really is? This is what I think it is: rotating motion of water when a particle travels at a ...
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364 views

About how fast can a small fish swim before experiencing turbulent flow around its body? [closed]

About how fast can a small fish swim before experiencing turbulent flow around its body? An Engineering Problem! Please go through this question step by step. :D
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162 views

How to calculate fluid(oil / hydrocarbon) loss under pressure

I'm trying to calculate the amount of fluid that would flow through an area dependant on the amount of pressure that there is. I'd also like to know the rate at which it would flow. Essentially I ...
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1answer
271 views

Will Buoyant Force Change If The Container is Accelerated Up or Down?

If we have a fluid which is in a container that is accelerated, say, upward by $a$. Then, what will be the buoyant force on an object with volume $V$, Density of liquid, $\rho$? I believe it will be ...
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305 views

How does the pressurization in a house's water supply allow adjustable flowrates from a tap?

John Rennie's answer to this question got me thinking about the water supply in a house. I know that water supplies are normally operated at an over-pressure with respect to atmospheric pressure to ...
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2answers
511 views

Differences in the behaviour of pinching a garden hose and closing a tap

Let's say you have a garden hose connected to an ordinary water tap which is opened fully. If you pinch the end of the hose, water leaves the hose at a higher speed (and this can be useful while ...
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1answer
163 views

Smoothed Particle Hydrodynamics, Chemical Reactions and Stiffness [closed]

Dear people from stackexchange physics. I have been using SPH for quite a while to simulate free boundary flow, and just recently we tried to include some kind of (simple) chemical reaction in our ...
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1k views

Deriving shallow water equations from Euler's equations

I would like to derive the one-dimensional shallow water equations from Eulers's equations. This works perfectly for the conservation of mass. Especially the meaning of the longitudinal fluid ...
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94 views

Conservation of mass in fluid flow

When deriving the continuity equation in physics class for two immiscible fluids flowing in succession we used the principle of conservation of mass. My question is, shouldn't volume be conserved ...
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1answer
105 views

What is the physics concept in sponge filter

I really need help I want to ask what is the physics concept in Sponge Filter?
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1answer
149 views

Energy conservation at a the end of a hose pipe?

I am trying to figure out the energy balance at the end of a hose pipe with water pouring out. Applying Bernoulli's equation inside the pipe we have three energy terms: Kinetic energy, "pressure" ...
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1answer
346 views

Pipe in a flowing river problem

I'm working on a certain problem in fluid mechanics, which isn't really my strongest area. The problem is as follows: Curved pipe is partially submerged in a flowing river so that one end is pointing ...
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60 views

Approximating density from pressure and flow

I want to get the density of a fluid going through a pipe. I can measure the flow and pressure with a flowmeter and the temperature using a thermometer. With this information, I want to calculate ...
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3answers
190 views

Spontaneous motion in a wind tunnel

Suppose that a hollow truncated cone is placed in a wind tunnel with a steady wind speed $V$. The cone is placed in such a way that it's base of area $A_1$ faces the wind (rather than the other side ...
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1answer
170 views

Does the space between molecules have no pressure?

In any living organism there exists are space between cells filled with interstitial fluid. Loss of this fluid into abnormal areas (3rd spacing) can cause relative to severe hypo-volemia. The fluid ...
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1answer
634 views

Why does a container with fluid make different sounds at different fluid levels?

Have you ever noticed that when you are filling a container with fluid. As it approaches the top, it makes a different sound? You can tell by listening when your about to reach the top. Why is this?
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822 views

How fast does the water travel down river when the discharge gates of a large dam are opened?

How fast does the water travel down river when the discharge gates of a large dam are opened? Can the discharge-wave travel downstream faster than the water? Is this likely to occur for a real river ...
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2answers
94 views

Air pressure in closed (circular) tube

I have learned that for fluids and gases $P_\text{total}=P_\text{dynamic} + P_\text{static}$. Suppose we have a closed circular tube in a form of ring filled with air under some pressure. In this ...
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4answers
365 views

Pressure in fluid mechanics of incompressible liquid

Most liquids can be approximated to be incompressible, since the Mach-number is much smaller than 1. That means that the density variations are negligible and from the relation between pressure p and ...
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1answer
278 views

When to use ideal gas law in fluid mechanics?

The ideal gas law (aka the equation of state) is given by $$ p/\rho_N = k_BT, $$ where $\rho_N$ is number density. When am I allowed to use this to describe a fluid?
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3answers
2k views

How to freeze the Niagara waterfalls?

Here is a picture of the usual vigorous Niagara Falls (in the winter). Here is the picture of Niagara Falls frozen in 1933 (in the very cold winter). Here is the picture of Niagara Falls frozen in ...
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1answer
130 views

Transport theorem derivation question

I am trying to rigorously go through some fluid mechanics proofs and theorems. I am currently going through a proof related to the transport theorem and I am having trouble with a step. The steps in ...
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3k views

Festive physics: gold flake vodka

I have a bottle of vodka that has a load of gold flakes suspended in it. It has been sat still for over 24 hours and the flakes are all still suspended within the liquid: they have not risen to the ...
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1answer
170 views

Is it possible to use the parabolic shape of a rotating fluid to measure the angular frequency of the rotation of the Earth?

A fluid in a rotating bucket will take on a parabolic shape (for example of some simple derivations of this result see http://en.wikipedia.org/wiki/Bucket_argument). The assumptions that play into the ...
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1answer
195 views

Acceleration of particles in a pipe with variable cross section

I am currently making an exercise from Paterson,1983, IV.3.ii. It goes as follows Water flows steadily and incompressibly along a pipe whose area cross section $A(x)$ varies slowly with the ...
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219 views

Maximum liquid velocity in a siphon

According to wikipedia: Siphon, the velocity of liquid in a siphon is equal to $\sqrt{2gh}$, where h is the difference in level between the water surface and the opening of the siphon. But it also ...
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372 views

What is the aperture in the hydraulic analogy of Ohm's law

Note: My question is duplicate of Why doesn't water come out of tap/faucet at high pressure when I turn it on?. None of the answers given there explains how the continuity equation fits properly. ...
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1answer
96 views

shear and normal stresses

When we talk about shear stresses in a fluid, we find that the shear stress is given by $$\tau_{xy} = \mu(\partial_y u + \partial_x v) = \tau_{yx}$$ This relation we get when only looking at one side ...
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13k views

Does pressure drop across pipe affect flow rate?

Let's say there is a main pipe containing $100\: \mathrm{m^3/hr}$ a fluid of density $750\: \mathrm{kg/m^3}$ and it's gonna be branched into 2 pipes (Pipe A and Pipe B) of the same diameter. If Pipe A ...
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209 views

Units of the PDF in the Lattice Boltzmann Method

In the Lattice Boltzmann method we require (based on mass conservation) that the sum of the distribution functions for a node is equal to the density, i.e. $$ \sum_i f_i = \rho $$ But what units do ...
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2answers
2k views

Physical description of momentum flux tensor

In the field of fluid mechanics, what is the momentum flux tensor? Is there an easy explanation for how it "works"?
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238 views

Freezing water in a closed container [duplicate]

We know that density of ice reduces by about 8% during freezing, this means it expands to have little higher volume. But if I fill water in a container (entire volume) which has very low coefficient ...
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1answer
118 views

Pressure difference between 2 side of wings of aircraft

I understand why the pressure is reduced above the wings of aircraft, but when I read books and look for information, it says that the air is compressed below the wings, I do not understand why it is? ...
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78 views

What will happen to a compressible fluid filled inside a sealed container when the container begins to accelerate?

Assume the fluid to be air and the container to be a car, will there be a pressure gradient which will result the fluid to stack at one end of the car or there is something else that I'm missing?
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249 views

What is a projection method?

Quoting from Solenthaler et. al. Predictive-Corrective Incompressible SPH (ACM Transactions on Graphics, Vol. 28, No. 3, Article 40, Publication date: August 2009) (PDF link here) These ...
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1answer
103 views

Estimate the time spent along fluid flow

I have a 2d flow field with a singular point $$\dot x=y-px^2\\\dot y=-x-qy^3$$ where $p,q$ are small parameters. How do I compute the cost time of a particle from $(x_0,y_0)$ to ambient of the ...
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277 views

What kind of energy does superfluidity use?

Liquid helium (and other similar fluids) can "climb up" the walls of their containers. Who does the work in this case, and what kind of energy does it use? I'm sure we can't make a perpetuum mobile ...
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49 views

Streamlines in Boundary Layer

Suppose that a fluid is flowing parallel to and over a flat plate. Obviously, a boundary layer develops in which the velocity ranges from 0 to 99% of the upstream velocity U. Could somebody please ...
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1answer
457 views

Pressure difference in u tube

Suppose you have a U tube filled with a liquid. The height of the liquid column in both the arms of the U tube is not the same. Will the pressure be the same at two points in the two arms of the U ...
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2answers
93 views

Relative velocity decomposition

In my fluid dynamics course notes is stated a change in relative velocity can be decomposed: $$\delta \mathbf{v} = \left\{ \begin{pmatrix} \Delta & 0 \\ 0 & \Delta \end{pmatrix} + ...
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3answers
519 views

Is there any solution to the potential flow around a square cylinder?

Potential flow around a circular cylinder is a classic solution. But I am wondering if there is any solution similar to this for the flow past a square cylinder?
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2answers
222 views

What is the symmetry associated with the local particle number conservation law for fluid?

According to Noether's theorem, every continuous symmetry (of the action) yields a conservation law. In fluid, there is a local particle number conservation law, which is ...
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2answers
151 views

Rayleigh-Taylor Instability dependence on acceleration direction

I'm trying to bolster my understanding of the Rayleigh-Taylor instability, and I've gotten stuck on the point of which fluid (more or less dense) is being accelerated into the other. Cases of uniform ...
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181 views

Speed of ejection of liquid from revolving tank

Consider a cylindrical tank filled with a liquid. Suppose it has an orifice somewhere at the bottom and the liquid is spurting out of this hole at a certain velocity. Now, if you rotated this cylinder ...
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1answer
480 views

Physical interpretation of the Lorenz system

The Lorenz equations $$ \frac{dx}{dt} = \sigma(y-x);\\ \frac{dy}{dt} = x(\rho-z)-y;\\ \frac{dz}{dt} = xy - \beta z $$ were (I believe) the first set of nonlinear equations known to exhibit chaotic ...