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

learn more… | top users | synonyms (1)

0
votes
1answer
62 views

How to 'smooth/flatten' the surface of a disturbed liquid

I would like to essentially flatten or smooth the surface of a viscous liquid after dropping an object into it, without actually touching the liquid. For example, if I drop a rock into a tub of oil, I ...
2
votes
1answer
91 views

Hyperbolic flow / vector field - irrotational and divergence-free?

My text book on meteorology claims that a hyperbolic flow pattern is both divergence-free and irrotational: (d) Hyperbolic flow that exhibits both diffluence and stretching, but is ...
0
votes
2answers
42 views

Is the Earth's molten outer core affecting its motion?

According with the seismological studies [1] the outer core, with thickness of about $2300km$, starting from depth of $2,900 km$ and ending at $5,200 km$ is a low viscosity fluid, consisted mostly of ...
0
votes
1answer
42 views

Velocity of a liquid jet, coming out of a container

Think of a container which has a hole beneath it. And we have filled the container in height $h$ with a liquid of density $\rho$ and cross section of the hole $a$. (look at the pic) Then what is the ...
5
votes
1answer
58 views

Flow through a rifled pipe

In turbulent flow the friction is inertial for the most part: the chaotic flow causes the fluid in the faster moving center to interchange randomly with the fluid near the edge. This eventually allows ...
1
vote
0answers
39 views

Does it take energy to destroy the surface of a liquid jet? [closed]

Imagine we have a collision of a liquid jet with an obstacle Does it take time for the surface of the jet to be destroyed while collision?? Or it'll be destroyed immediately?
1
vote
1answer
150 views

Can a vacuum make a turbulent flow laminar?

When a vacuum is generated next to a turbulence, does the flow towards the vacuum become laminar? Imagine a vacuum cleaner tube is put next to turbulent air movement, does the "suction" change the ...
4
votes
4answers
175 views

Does steady flow imply laminar?

Most secondary school textbooks, in their chapter about fluid dynamics, seem to suggest that "steady flow" and "laminar flow" are synonyms. Though I never received any fluid mechanics course when I ...
6
votes
4answers
6k views

What is the exact difference between diffusion, convection and advection?

I have tried to explore the information but still not very clear on the exact difference between diffusion, convection and advection. Can anyone help me out to clear my concept?
1
vote
0answers
44 views

standing waves on a cylindrical jet

as we know, there are some perturbations on a falling jet which are always present and according to their wave number and the radius of the jet, they can grow and decay over time. so, imagine a jet ...
0
votes
0answers
31 views

The change in time of a concentration in a fluid can be described by Reynolds' theorem. Is that the whole story?

Let $d\in\left\{2,3\right\}$ and $\Omega_t\subseteq\mathbb R^d$ be the bounded set occupied by a fluid at time $t\ge 0$. Moreover, let $\eta_t:\Omega_t\to[0,\infty)$ be the concentration of imaginary ...
2
votes
1answer
261 views

Perfect fluid and Cauchy momentum equation

The stress-energy tensor of a perfect fluid is given by $$T^{\mu\nu}=\left(\rho+pc^{-2}\right)u^\mu u^\nu+pg^{\mu\nu}$$ The divergence of the stress-energy tensor is zero: $\nabla_\mu T^{\mu\nu}=0$. ...
3
votes
1answer
59 views

Waves: Small Amplitude Approximation

Why does the assumption of waves amplitude being small, compared to the wavelength, (as used for surface gravity waves in water) lead to the equivalent condition: $$ {\partial v \over \partial t } ...
2
votes
2answers
292 views

Gas pressure and centrifugal force

I think about a rotating torus (simplified tire) filled with ideal gas. Mass of gas is $m$ and molar mass is $M$. Pressure in non rotating torus is $p_0$. Temperature is constant $T$. Inner radius of ...
3
votes
0answers
94 views

Dark matter “hair” flowing through the earth

Gary Prézeau of NASA's JPL has done some calculations of how dark matter might be focussed by the Earth's gravitational field (publication preprint), and the results show some remarkable hairy ...
2
votes
1answer
29 views

The validity of constitutive diffusive fluxes

In transport phenomena the diffusive fluxes for mass, energy and momentum are the constitutive laws: $$\boldsymbol{j}_c=-D\boldsymbol{\nabla}c \quad \boldsymbol{j}_T=-k\boldsymbol{\nabla}T \quad ...
1
vote
0answers
26 views

Height of water in vessel containing gas [closed]

The question reads- Thin walled Cylinder of height h, mass m and cross section A filled with gas and floats on water. Now due to leakage depth of submergence increases by $\Delta h$. $P_o$ is the ...
0
votes
0answers
16 views

Force of Leaky Bucket over time

Indie Lab Procedure: I attached a cylindrical can to a force sensor. On the bottom of the can I drilled holes of various diameters. I then added a volume of water while collecting data from the force ...
0
votes
1answer
41 views

Rate of flow of water fluid mechanics

If we have a cylindrical tank of area $A$ which has a small outlet of area $a$ at the bottom of the surface . And the container starts filling with a constant rate $k [m^3/sec]$ . Now the max. level ...
0
votes
0answers
13 views

Plateau–Rayleigh instability according to liquids $Ca$ number

For examining whether viscosity or surface tension dominates each other effects, we can't refer to $Re$ or $We$ numbers because they just tell us about one of them ( surface tension and viscosity ). ...
0
votes
1answer
28 views

What is the different between Poisson Nernst–Planck and Poisson Navier–Stokes in the Electrolyte?

I am now studying about electroosmosis flow phenomena which is governing by the Navier-Stokes equation and Poisson equation. By combine these two equation we can describe the electrolyte flow velocity ...
0
votes
0answers
13 views

Breakup of liquid jet hitting another liquid surface: Droplet size?

If a jet of liquid #1 impacts the horizontal surface of liquid #2, liquid #1 will break up into dispersed droplets below the surface of liquid #2. (The liquids are immiscible.) Is there a method for ...
1
vote
0answers
30 views

Flow of liquid through pipe [closed]

As in the figure there is a horizontal pipe through which liquid is flowing. And three tubes are connected A, B and C where the radii are 2 cm, 1 cm and 2 cm. Then what would be the height of liquid ...
2
votes
0answers
31 views

How fast does water have to be moving for it to gain a lot of heat? [duplicate]

A random question popped into my head a few minutes ago: objects, when moving fast enough, start to get resistance from the air. Since there is friction between the air and the object [water], there ...
2
votes
1answer
40 views

Surface energy of water [closed]

If $10^3$ small drops of water each of radius $10^{-7}\,\mathrm{m}$ combined to form one single large drop then what should be the energy ? If the surface tension is equal to $0.07\,\mathrm{N/m}$ . I ...
0
votes
1answer
31 views

Plateau–Rayleigh instability for liquids with low $Re$ number

I'm working on a project about Plateau–Rayleigh instability for liquids. But I've a question. we can examine the fluids with high $Re$ number that the influence of viscosity is negligible, but what ...
0
votes
2answers
33 views

Barometer barometric pressue

the barometric pressure and height on earth are 10^5 pa and 760 mm respectively . Then what is barometric height if it is taken at moom . I think at moon the gravity will decrease then pressure ...
0
votes
1answer
33 views

Aircraft lift theory vs energy conservation [closed]

I spent years trying to find out that when an aircraft flies or anything works it consumes energy more than it delivers back, means no perpetual motion exists. My query is that when an aircraft is at ...
24
votes
2answers
2k views

When a drop of water falls into water, where do the splashes come from?

When a drop of water falls into a reservoir of water from a high enough altitude, water droplets will splash (image credit): My question: Does the water in those droplets come from the original ...
2
votes
1answer
295 views

Flow rate through hole at bottom of tank, estimate time for depth to reach 1 foot [closed]

I am a structural engineering student and have limited experience in fluid dynamics. I'm not quite sure if I'm going about the problem in the correct way. The question is: An open cylinder of ...
0
votes
0answers
28 views

Pressure difference along horizontal in accelerated fluids

In accelerated fluids, fluid in a container can orient itself in a direction due to acceleration. In that case, pressure at different heights (at the surface) is same (atm). Then at the same height, ...
0
votes
2answers
82 views

Torricelli's speed of efflux law

Torricelli's law states that if we make a hole in a container of fluid open to atmosphere, then the speed of the fluid spouting out is: $$\sqrt{2gh}$$ Does this velocity correspond to the horizontal ...
1
vote
1answer
66 views

Why does my coffee stop?

As I was mixing my coffee this morning, wishing that it would do it on its own, I started wondering: What makes my coffee stop swirling? I mean what exactly? Is it the walls of the cup or the coffee ...
1
vote
1answer
20 views

How can pressure and velocity fluctuations in acoustic plane waves be in phase and still hold to the B.C. that velocity must be zero at a solid wall?

In linear plane-wave acoustics (no mean flow, small perturbations, etc.), it is often derived that the phase of a traveling pressure fluctuation wave and a fluctuation velocity wave are the same. For ...
9
votes
2answers
365 views

The optics of vortex (in water): why there is a bright ring?

This picture is from this YouTube video from "Physics Girl", which shows how you can generate vortices in a swimming pool by using a plate: And there she explains the creation of the shaded circle ...
0
votes
0answers
54 views

What is an intensive property of a fluid?

Let's assume we are considering a fluid which occupies the bounded domain $\Omega_t\subseteq\mathbb R^d$ at time $t\ge 0$. Let $c\in\Omega_0$ be a particle of the fluid and $$x_c:[0,\infty)\to\mathbb ...
1
vote
3answers
118 views

General Definition of Steady State

According to many sources (including Wikipedia, Stephani&Kluge, D.J. Acheson) a steady state ist: In systems theory, a system in a steady state has numerous properties that are unchanging in ...
3
votes
3answers
3k views

The pressure in a water spout and Bernoulli's equation

This is a conceptual question about the application of Bernoulli's equation to a water spout. There is a classical problem found in many physics texts which goes something like "you have a garden ...
1
vote
1answer
27 views

Does *advection* describe the change of density of massless infinitesimal tiny *thingies* injected into a fluid?

I'm considering an incompressible Newtonian fluid with uniform density and try to figure out what's meant by the term advection. Let $\Omega_0\subseteq\mathbb R^d$ be an (infinitesimal small) bounded ...
10
votes
2answers
2k views

How much of the forces when entering water is related to surface tension?

When an object enters water with high velocity, (like in Why is jumping into water from high altitude fatal?), most of it's kinetic energy will be converted, eg to accelerate water, deform the object ...
1
vote
0answers
60 views

The Optics of the Vortex (in Water): why there is a bright ring also in reversed flow?

This question is closely related to this one; The optics of vortex (in water): why there is a bright ring? In this case "physics girl" gives somehow an plausible explanation, and it's only debatable ...
1
vote
2answers
43 views

why is pressure more convenient than force while dealing with fluids? [duplicate]

If two equal and opposite forces act on a surface, can I say the pressure is zero because the net force is zero? How can pressure be non directional when force as a direction? How can the pressure of ...
0
votes
0answers
18 views

Effect of heating a fluid

When a liquid or a gas is heated from below, the fluid terms to organise itself into cylindrical rolls. Can anybody help me in reasoning why so?
0
votes
1answer
49 views

Rate of applied force versus material failure?

Question: Does the rate at which a force is applied to an object determine the maximum force reached that mechanically fails the object? If so, what are the concepts that need to be understood to ...
0
votes
1answer
19 views

Pressure Change in Supersonic Wind Tunnel [closed]

As far as I know, the total pressure changes across a shock wave. How is this possible if you are in the atmosphere and atmospheric pressure isn't changing? Is energy lost due to entropy in ...
6
votes
4answers
895 views

How does a converging-diverging nozzle not violate conservation of energy?

Disclaimer: I know absolutely nothing about fluid dynamics, and very little about physics in general. THis may be a really dumb question. Now, at subsonic speeds, converging and diverging nozzles ...
0
votes
1answer
61 views

How do fluids behave in space?

In outer space under absence of any external force (like gravity) can a free liquid develop pressure due to cohesive forces? Will the liquid be in spherical shape and will pressure increase towards ...
0
votes
0answers
24 views

Pressure Variations due to Flow in an Inviscid Fluid

Let's say we have an irrotational, inviscid fluid with steady flow. Then the Bernoulli function (ignoring gravity) $$H=\frac{p}{\rho}+\frac{u^2}{2}$$ is constant everywhere. My notes then make a jump ...
0
votes
1answer
51 views

How to calculate the speed of a jet of liquid coming out of a nozzle? [closed]

I'm working on a project and i need to calculate speed of a jet falling from a nozzle. But my question is that, is it correct to use $$v=\sqrt{2gh}$$ Or should the speed of the jet be independent ...
1
vote
0answers
25 views

Period of small oscillations of liquid in a bottle

I have seen that water in a bottle of water when perturbed invariably starts oscillation back and forth, with the shape of the water surface remaining intact. I was wondering if there was any way to ...