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

learn more… | top users | synonyms (1)

5
votes
1answer
125 views

The Mysterious Reverb in a Jar of Hair Gel

I have a small jar filled with hair styling gel (or, as it calls itself: Ultra Gel-Wax). The jar is cylindrical(with the height being less than the width), has an unscreweable lid and is made of ...
5
votes
2answers
104 views

In turbulence theory, what happens if i take space average of fluctuating part?

According to Reynolds decomposition, velocity field is split into two time average and fluctuating parts: $$u_{({\bf x},t)}=\overline u_{(\bf x)}+u'_{({\bf x},t)}$$ we know that time average of ...
5
votes
3answers
686 views

When is a flow vortex free?

To solve problems in fluid dynamics one states often the assumption that the flow is vortex free i.e. $rot(u) = 0$ It is a basic assumption which is needed for potential flow problems etc.. My ...
5
votes
2answers
593 views

What causes acceleration of particles in the expansion section of a De Laval nozzle?

A De Laval nozzle has a compression section, where the propellant is compressed (and thereby accelerated) as it moves towards a narrow section (the throat). After the throat, the nozzle widens out ...
5
votes
1answer
184 views

Increment of surface tension with increase of temperature

What is the reason for the increase in surface tension of molten copper/cadmium with increase in temperature?
5
votes
2answers
728 views

Solving the Young-Laplace equation for arbitrary axisymmetric geometry

Say I have a non-ellipsoidal soap bubble and I want to numerically analyse the pressure in the inner lobe of this bubble here: The Young Laplace equation gives the pressure difference across a ...
5
votes
1answer
843 views

Paper plane between two fans - is this possible?

The setup: two fans facing each other, distance around 1m. Both are turned on. In between them, place a simple paper plane and according to this video, it will fly. ...
5
votes
1answer
459 views

What is the roaring in a roaring fire?

I was just starting a barbecue fire by blowing on the smouldering coals when I realised I had no idea what the sound was actually caused by. I can make the sound by blowing at almost any flame I can ...
5
votes
1answer
195 views

Why do rain waves form and what is their connection to the texture of the surface they're on?

When it rains and water flows down an inclined street, ripples may form that are carried along with the current. Here's a picture with an example of what I'm talking about I'd like to know what the ...
5
votes
2answers
96 views

Does vortex shedding exist along the surface of an object?

Vortex shedding occurs due to the detachment of flow. The typical example is for the oscillating wake behind a cylinder, and has a frequency related to the size of the object. I want to know, if a ...
5
votes
1answer
107 views

Sailing against the wind. Is this a fair model?

I was ruminating the explanations about how boats can sail against the wind, and wondered if one can devise a simple mechanical model without hydrodynamics involved. Imagine a cart (in red in the ...
5
votes
1answer
362 views

Why does the milk frother on my coffee machine make so much noise?

I have a Sunbeam home espresso machine with a steam wand. The steam roars out straight from the end of the wand. When it's first placed in the cold milk it really screams! Once the milk has a bit of a ...
5
votes
2answers
87 views

Influence of choice of statistics on gas kinetics

In the derivation of distributions over energy states, a common assumption made is that under normal conditions (normal from a fluid dynamics standpoint, so > 300K typically) the energy states are ...
5
votes
1answer
581 views

Scale dependence of energy dissipation in viscous flow via AdS/CFT

The famous AdS/CFT calculation of the shear viscosity/entropy ratio for strongly coupled $N=4$ SYM relates the shear viscosity to the absorption cross section for fluctuations of the metric onto a ...
5
votes
2answers
66 views

Does space have a “radiation pressure” caused by subatomic particles?

If space is not actually a void, then there's something shooting around in it, I'm guessing a lot like molecules in a gas. Could we apply a $(PV/T = k)$ -like gas law to it. Obviously we're not ...
5
votes
0answers
49 views

Time inversion for Euler equation

Consider Euler equation for continuum body: $$\frac{\partial u^i}{\partial t}+\mathbf u\cdot \nabla u^i=- \frac{1}{\rho} \frac{\partial p}{\partial x^i} $$ where $\rho$ is the mass density, $p$ is ...
5
votes
1answer
61 views

How to estimate the time spending along the 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 ...
5
votes
0answers
315 views

Can a divider “laminarize” turbulent flow and thus reduce friction?

Looking at the Moody chart I think to myself, the friction factor doesn't decrease much at all with Reynolds number after a certain point. I wonder if laminar flow is more efficient in a sense, and ...
5
votes
1answer
331 views

Lotus effect dust removal

I have found hundreds of papers describing the contact angle of water droplet sitting on hydrophobic surface and the change between Wenzel Regime and the Cassie-Baxter regime. Now, as I understand ...
5
votes
0answers
300 views

What's the efficency of a steam jet pump?

Jet pumps or venturi pumps are often stated as having a "terribly low" efficiency, steam jet pumps specifically are usually describes as "only justifiable when there's an abundant steam supply anyway" ...
5
votes
4answers
685 views

A quantitative explanation of EM coherence domains in liquid with DNA

I've been looking with interest at a recent biology paper claiming that DNA molecules give off electromagnetic signals which can cause the same types of molecules to be reconstructed at a remote ...
4
votes
1answer
288 views

Can a hovering helicopter travel half the globe in 12 hours? [duplicate]

Suppose we have a helicopter that is able to stay stationary in flight for extended periods of time. If such a helicopter stayed at point A in the sky for 12 hours straight, would it reach the other ...
4
votes
1answer
1k views

Why, when one opens 1 car window, does that noise occur?

When you're driving and you open 1 car window, say the front one, there comes a horrible noise, but when you open another window just the slightest bit, this noise goes away (I'm sure most people know ...
4
votes
3answers
1k views

What cools a drink?

When you stick ice in a drink, AFAICT (the last physics I took was in high school) two things cool the drink:The ice, being cooler than the drink, gets heat transferred to it from the drink (Newton's ...
4
votes
3answers
295 views

atmospheric phenomenon? What causes condensation trails to converge?

This air plane just caught my eye. Two contrails apparently are flowing backward, slightly off-centered and then ultimately converge, giving the overall shape of a very narrow rhomboid parallelogram, ...
4
votes
2answers
2k views

Conservation Vs Non-conservation Forms of conservation Equations

I understand mathematically how one can obtain the conservation equations in both the conservative $${\partial\rho\over\partial t}+\nabla\cdot(\rho \textbf{u})=0$$ ...
4
votes
2answers
397 views

When water is about to boil

Have ever noticed? When water is about to boil, no matters the kettle, there is some sound I have no idea where it comes from, sometimes long before it boils. Is there any explanation for this ...
4
votes
1answer
1k views

Exact Solutions to the Navier-Stokes Equations

There are a number of exact solutions to the Navier-Stokes equations. How many exact solutions are currently known? Is it possible to enumerate all of the solutions to the Navier-Stokes equations?
4
votes
3answers
359 views

How can I keep a smaller water reservoir's water level at half available when being fed from a larger reservoir? [closed]

I'm trying to create my own ultrasonic humidifier. I ordered the misting part which works great but it only functions correctly in shallow water. So I'd like to feed from a large water reservoir to a ...
4
votes
3answers
5k views

What is the physical meaning of diffusion coefficient?

In Fick's first law, the diffusion coefficient is velocity, but I do not understand the two-dimensional concept of this velocity. Imagine that solutes are diffusing from one side of a tube to another ...
4
votes
2answers
5k views

Flow of liquid among branches

If water is flowing through big pipe is branched into 4 branches of small pipe. Lets say the flow is around 4 m/sec. I have the following questions: What will be the flow rate in each of the ...
4
votes
2answers
1k views

Frequency of Vortex Shedding

Suppose we have a long cylinder with diameter $D$, then we move it parallel to its axis with a velocity $V$ in a medium such that the Reynolds number of the flow is in the range ...
4
votes
3answers
1k views

How is the Joukowsky Transform used to calculate the Flow of an Airfoil?

As I read in The Road to Reality by Roger Penrose, the Joukowsky transform $$w(z) = \frac12\left( z + \frac1z \right)$$ after Nikolai Zhukovsky (transcribed in several versions from Никола́й Его́рович ...
4
votes
2answers
1k views

Reynolds number and inertial force

The Reynolds number is defined as the ratio of ´inertial´ forces to viscous forces. $$ Re = \frac{\text{Inertial Forces}}{\text{Viscous Forces}}$$ Now, viscous forces make sense to me. They are ...
4
votes
4answers
345 views

What is the term for hose fluctuating movements during flow?

What do we call it when water flowing through a flexible hose causes it to act like snake movements if the hose were disturbed? Can this movement be explained by the Coriolis force?
4
votes
2answers
734 views

What do the dimensions of circulation mean, and how is circulation related to action?

The dimensions of circulation $\int_C \vec{v}\cdot d\vec{r}$ seem strange, but if you include (even a constant) density $\rho$, then $\int_C \rho\vec{v}\cdot d\vec{r}$ has dimensions the same as ...
4
votes
2answers
181 views

What is the motivation behind $\tau=\mu \frac{\mathrm{d}u}{\mathrm{d}y}$ for Newtonian fluid?

Where does the motivation come from? $\tau$ is the shear stress, $u$ is the velocity and $\mu$ is the shear viscosity. EDIT: Since I wrote the question on phone I wasn't clear enough about what I ...
4
votes
2answers
112 views

The velocity of a cloud?

I noticed an unusually fast moving cloud this morning. My questions: What is the average velocity of a cloud on Earth? What is the greatest ever recorded cloud velocity? What factors affect the ...
4
votes
1answer
134 views

Fluids in thermodynamic equlibrium

I am reading about the Euler Equations of Fluid dynamics from Leveque's numerical methods for conservation laws. After introducing the mass, momentum and energy equations, some thermodynamic ...
4
votes
2answers
861 views

Why do cars gain lift while going at a high speed?

I've been researching the physics involved with spoilers and I've just been turning up the same information about spoilers giving the back wheels of a car more traction by acting as an up side down ...
4
votes
4answers
2k views

How far can water rise above the edge of a glass?

When you fill a glass with water, water forms a concave meniscus with constant contact angle $\theta$ (typically $\theta=20^\circ$ for tap water): Once you reach the top of the glass, the water-air ...
4
votes
1answer
241 views

Does water need to pumped up from deep ocean?

OTEC (Ocean Thermal Energy Conversion) utilizes the temperature gradient between cold deep ocean water, and warmer water to do work. I understand the pressure in the depths may be as high as a couple ...
4
votes
1answer
329 views

Why do sea levels not rise uniformly around the world?

While reading the article Hawaii’s Beaches Are in Retreat, and Its Way of Life May Follow on The New York Times's website, I was surprised to find out that sea levels do not rise around the world at a ...
4
votes
2answers
387 views

Multiple source Pipe Network: Given a known outflow, can we deduce the inflows?

I have the following simple Y shape water pipe network: Given $S_{out}$ ( in $m^3/s$), can we compute $S_1$ and $S_2$? For the pipe, we know for each pipe their corresponding diameter $d$, length ...
4
votes
1answer
1k views

Why do steam bubbles increase in size as they rise?

In the following video (a customer's review of a glass kettle), we can observe water boiling: http://youtu.be/jByY5I7Xk7w?t=2m55s As the kettle starts to boil at around 2:55, we can see large steam ...
4
votes
2answers
202 views

At what size will self-gravitation contribute more to stability than surface tension?

The governments of Earth have embarked on an experiment to place a massive ball of water in orbit. (umm... special water that doesn't freeze) Imagine this to be a fluid with a given density, $\rho$ ...
4
votes
1answer
402 views

Fluid Mechanics from a variational principle

It is posible to define a good variational principle to describe Fluid Mechanics? if so, wath is the correct tratement of the issue. I guess something like: $I=\int d^4x (\frac{1}{2}\rho v^2-P-\rho g ...
4
votes
2answers
166 views

Autocorrelation of sound in liquids vs gas

This is just a curiosity and you need to bear with me as my math skills were always sub-par and so is my English academic language. My specialty is Electronics but I have always been a programmer. ...
4
votes
2answers
79 views

Physical interpretation of the change of diffusion term in navier stokes equations

In the Navier-Stokes Equations, there is one term accounting for convective flow and one term for diffusive flow. At high flow rates, the diffusive term becomes much smaller compared to convective ...
4
votes
1answer
100 views

where does the energy of water droplet go?

My experiment: I took a string (3 mm diameter and wet) and a water source (1 drops per 2 seconds). Then I attached the string to the water source. The string was then tied to ground Observation : ...