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

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Can ship/boat propellers be placed, with adequate protection, alongside the fuselage instead of at the back?

On small private aircraft the engine is placed at the front of the fuselage, or on the wings E.g. Stationair, Otter On combat aircraft the engine/s is placed at the end of the fuselage E.g. Raptor, ...
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124 views

How does a particle move in Water?

Is there any precise model (More precise than the random walk model) that describes a particle's movement in water ?
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271 views

Why is my ballpoint pen spatially temperamental?

I'm trying to write with a ball-point ink pen on a plastic[1] sandwich bag. When I try to write on some parts of the bag, no ink transfers to the bag: I can continue trying for quite a while in vain. ...
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94 views

how to stop water reaching up inside an under water structure (see video)

in this video at arround 0:47 they deliver the 'dry pots' to the under water lab, bellow the water and they seem to swim up into an opening where it is completly dry.. how is this dry, surly the water ...
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Why and how is sound produced when two objects hit each other?

When two objects collide and undergo a partially inelastic collision (so every one we experience in every-day life), they rebound to a certain degree, but kinetic energy is not conserved. Thus, the ...
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1answer
124 views

Flow of freezing liquid or a melting solid

If a liquid is freezing, is equation of continuity violated? As the liquid flows, some portion of it is getting frozen. The mass of the fluid thus keeps dropping. Similarly, when a molten fluid flows ...
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6k 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 ...
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Non-Newtonian Fluid Stop a Bullet?

I just saw a YouTube video about Non-Newtonian fluids where people could actually walk on the surface of the fluid but if they stood still, they'd sink. Cool stuff. Now, I'm wondering: Could a pool ...
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2k views

Why is pressure in a liquid the same in all directions?

I'd like answers both in the more intuitive side an on the more precise side. Thinking of water as "cubes" of water, for example, would allow pressure in the z axis to be independent of the y or x ...
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298 views

How would this rapid depressurization of water really behave?

An in-development game(Starbound) recently released a demo of their water physics. At about 39 seconds into the video, a volume of water in a container is released when the cap on the container is ...
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2k views

Why does water flow out of an upside-down bottle? (Rayleigh Taylor Instability)

I am currently reading the excellent book An Indispensable Truth: How Fusion Power Can Save the Planet by Francis F. Chen and I came across this explanation. The Rayleigh–Taylor Instability ...
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1answer
577 views

Glass - paper: Stevin's Law

In my understanding the well-known experiment of the glass full of water in equilibrium with a piece of paper, the atmospheric pressure acts on a small layer inside the glass (on the top) and under ...
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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. ...
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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 ...
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1answer
126 views

Which topics & books should I read to understand whirlpool, tornado, hurricane etc.?

I want to be expert to understand physics behind whirlpool, tornado, hurricane. Which topics are needed for this?
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1answer
176 views

Pressure loss after water goes up and back down 7 stories

I live on the first floor of a seven story apartment building. We are considering our hot water options and one of them is a solar-powered water heater in which water is heated in a specialised device ...
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2answers
240 views

What equations govern the formation of droplets on a surface?

When some smooth surface (like that of a steel or glass plate) is brought in contact with steam (over e.g. boiling milk) then water is usually seen to condense on that surface not uniformly but as ...
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934 views

How is the stickiness of a fluid measured?

How does one compare the "stickiness" of different substances on a certain surface? For example: Does glue A stick better to steel than glue B? Does water stick better to steel than oil?
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628 views

How is energy transferred from one incompressible fluid to another?

When you apply pressure to an incompressible fluid the pressure is transferred. If you stop applying the pressure there is no motion. Volume and density are integral parts of calculating how much ...
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1answer
237 views

What equations/constants were used to calculate the Kármán Line for Earth?

I am interested in how the original value of ~100 km was calculated for the Kármán line of earth. What equations and constants would need to be used to reproduce this value? Note: By constants, ...
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973 views

How can I calculate the flow rate necessary for a given cross sectional area, angle, and length

I'm making a toy for my kids and this problem came up. I have a channel on a slight angle (angle is between ground and length of channel) and I'm pouring water into it. I want to know how quickly I ...
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3answers
2k views

What is the principle behind centrifugation?

What is the principle behind centrifugation? I understand the idea that you spin something around the centripetal force will cause an apparent force on the spinning system. However I don't quite ...
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1answer
2k views

Is there an analytical solution for fluid flow in a square duct?

I couldn't find one but assumed it must exist. Tried to find it on the back of an envelope, but got to an ugly differential equation I can't solve. I'm assuming a square duct of infinite length, ...
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Does irrotational imply inviscid?

Let us consider a 2D irrotational flow, such that $\nabla\times\boldsymbol u =\boldsymbol 0$. Defining the stream function such that $\boldsymbol u =\nabla\times\psi \boldsymbol n$ where $\boldsymbol ...
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151 views

Does turbulence violate Galilean relativity?

Fluid flows become turbulent beyond a certain velocity. The velocity is almost always with respect to a fixed boundary. However, an observer in a frame of reference travelling with the fluid will also ...
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277 views

Can cannonballs go through water?

In the recent Spielberg/Jackson Tintin movie, there is a scene where Red Rackham and Captain Haddock's ships are fighting, and cannons are fired. The cannonball is shown at one point to go through a ...
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1answer
1k views

Continuity equation for compressible fluid

A question is given as Consider a fluid of density $ \rho(x, y, z, t) $ which moves with velocity $v(x, y, z, t) $ without sources or sink. Show that $ \nabla \cdot \vec J + \frac{\partial \rho ...
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Why airplanes fly: the final truth

The questions about the reasons the aircraft fly are frequent among scientist, since the high school until now, even if I work on the other side of fluid mysterious world (the Low Reynolds numbers ...
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1answer
214 views

Capillaries in series

The velocity of fluid of viscosity $\eta$ through a capillary of radius $r$ and length $l$ at a distance $x$ from the center of the capillary is given by; $v=\frac{P}{4l \eta }(r^2-x^2)$ (where $P$ is ...
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1answer
312 views

How to deal with conflicting “no-slip” Navier-Stokes boundary value constraints?

The no-slip boundary value constraint for Navier-Stokes solutions was explained in my fluid dynamics class as a requirement to match velocities at the interfaces. Now that my class is done, I've been ...
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Concentration of fluid pumped through a tube?

I have a bottle filled with a fluid A, and a tube of volume $V_0$ filled with a fluid B leading away from it. When I now start pumping fluid A out of the bottle, I am interested in the concentration ...
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206 views

What's the most efficient strategy to shake a bottle to create a global flow?

Consider a bottle of orange juice with pieces of the fruit gathered at the bottom of the bottle. You need to shake the bottle to evenly distribute the pieces in the bottle. The first part of the ...
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1answer
254 views

Darcy law yields extreme speed for gas flow throgh packed spheres?

The darcy law is as follows: $u=-\frac{k}{\mu}\nabla p$. Assume we have a gas, then $\mu$ is about $10^{-5}$. $k$ for packed spheres a few mm in diameter is of order $10^{-8}$ $m^2$. Say the ...
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533 views

Wind Turbine Impact

OK, I'm not sure this is not a silly question, but here goes. I've often wondered what the impact is of wind turbines on the weather. My question is, since wind turbines transform wind energy into ...
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1answer
545 views

Capillary engine is impossible?

I read some articles saying that it is not obvious (or maybe impossible) to generate energy using capillary action. On the other hand in my understanding trees uses capillary action to extract water ...
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1answer
129 views

How do Kolmogorov scales work in shear thinning fluis?

My understanding of Kolmogorov scales doesn't really go beyond this poem: Big whirls have little whirls that feed on their velocity, and little whirls have lesser whirls and so on to viscosity. ...
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1answer
365 views

How is external pressure transmitted when a fluid is not enclosed?

Pascal's principle states that pressure applied to an enclosed fluid is transmitted undiminished to every part of the fluid. How is the pressure transmitted in the case where the fluid is not ...
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1answer
914 views

How much water must flow trough canal to maintain a constant water deep?

In order to maintain a constant water deep in canal, how much water must flow trought the pipe ? As shown on picture, canal have a rectangular shape. I don't know if canal length have an influence. ...
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714 views

Vortex street and Reynolds number

Its been stated in Wikipedia regarding Reynolds number(Re) that "laminar flow occurs when Re<2300 and turbulent flow occurs when Re>4000. In another wiki file related to Kármán vortex street it has ...
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1answer
105 views

Critical bathymetric profile to maximize surge and minimize breaking?

Reading about storm surge, I found it fascinating that the gradual slope of the Gulf Coast of Florida resulted in a much higher storm surge but much lower energy release in breaking waves. Is there ...
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70 views

The sound of coffee [duplicate]

Possible Duplicate: Why does the sound pitch increase on every consecutive tick at the bottom of a filled cup of coffee? A colleague suggested this experiment this morning : Get a cup of ...
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1answer
319 views

Can we make an environment where the density of air equals the density of water?

Also, in case an environment with equal density of air and water can be made: Will it be possible for a human to breathe in that environment?
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2answers
499 views

How does Earth's interior dynamo work?

I'm interested in getting a basic physical understanding of how Earth's magnetic field is generated. I understand that it's a "dynamo" type of effect, driven by convection currents in the molten outer ...
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3answers
352 views

What is the microscopic picture for warm air rising?

The usual explanation for warm fluids rising past cooler ones is that the warmer fluid has a lower density. I'm trying to understand what this looks like at a molecular scale. The density seems to ...
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45 views

What is the fluid approximation for BCS action?

For a system with free fermion gas at finite density (i.e. free Dirac action), we have an ideal fluid description with rho, p, n. What is the fluid description for BCS action? Suppose we have a box ...
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1answer
369 views

Is it possible to calcualte the yield-stress of a fluid by measuring the smalles bubble that rises through it?

Consider a yield-stress liquid in gravity. I assume that the buyouncy of a small gas-bubble will not be enough to overcome the yield stress (so the liquid doesn't behave liquid), thus leaving the ...
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4answers
16k views

Why can't helicopters reach mount everest?

Is there a reason why people can't just take the helicopter to mount Everest? Why is it that helicopters can't reach that high?
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122 views

How to integrate twice of this viscous term?

I am reading a paper, and I do not understand why the author said the following term when integrated twice will become, $\int\limits_\Omega {{\rm{d}}\Omega {{\bf{\psi }}^{\bf{u}}}\cdot\nabla ...
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1answer
293 views

Confused about the physical meaning of velocity variation

I am reading a paper and saw the author wrote something like, Because of no-slip wall assumption, so velocity vector $\vec{v}$ is $0$ on the wall, and also the variation of this velocity on the wall ...
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Why does water pouring from a glass sometimes travel down the side of the glass?

If you have a glass of water, say, three quarters full and you pour it at an angle of say, $45^{\circ}$ with respect to the the table, the water comes out of the glass and goes directly down towards ...