The quantitative study of how fluids (gases and liquids) move.
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2answers
323 views
What is the dominant cause for ocean waves at a beach?
What is the dominant cause for ocean waves at a beach? Are they the result of wind/pressure difference? If so, the waves do seem to exist in similar intensity even during relative quiet times of the ...
3
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1answer
309 views
How to derive the Karman-Howarth-Monin relation for anisotropic turbulence?
I find the derivation of the Karman-Howarth-Monin relation in the book Turbulence from Frisch (1995) a bit to short. Can someone point me to a more detailed derivation of that relation, if possible in ...
2
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1answer
1k views
How to calculate the projected area at different angles/vectors?
Please help me with the following. I want to know if there is an equation/set of equations to find out the projected area of a (3-D) cube when it is oriented at different angles of attack to the fluid ...
5
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1answer
1k views
Why do some carbonated drinks fizz more than others?
Wired magazine ran an article this month on carbonation in soft drinks.
If all soft drinks are manufactured effectively identically, why do some types fizz more than others?
For example, root beer ...
3
votes
1answer
192 views
Olympic games and the local g
As you probably know, the two next Olympic games will take place in London and Rio. Randall, author of xkcd, did an interesting observation (that I had never thought of) in http://xkcd.com/852/ , ...
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1answer
478 views
Sutherland's constant of argon
I want to compute the viscosity of argon at different temperatures. What is Sutherland's constant of argon?
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2answers
166 views
How to calculate the effect of roof items on gas mileage?
I have a kayak and a bike. I routinely put them on top of my car and drive 60-70 mph for hundreds of miles. I am curious how much this affects my gas mileage.
1
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1answer
575 views
Fluid dynamics, flow of a 2D jet from a narrow slit
I'm working through some exam problems, and I came across this one - the solution of which baffles me considerably.
A two-dimensional jet emerges from a narrow slit in a wall into fluid which is ...
7
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3answers
457 views
Boundary layer theory in fluids learning resources
I'm trying to understand boundary layer theory in fluids. All I've found are dimensional arguments, order of magnitude arguments, etc... What I'm looking for is more mathematically sound arguments. ...
4
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2answers
1k views
Shape of Fan Blades
How is the shape of the blades of an air fan determined? Trial and error, or is there a theory behind it? What are they trying to maximize, volume of air dislocated per rotation?
2
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1answer
282 views
Coffee cooling in a cup
Will coffee in two differant size styrofoam cups in the same room conditions cool at the same rate? One cup is 8 oz. and the other would be 12 oz.
4
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2answers
352 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 ...
0
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1answer
191 views
What is it that makes this structure cause turbulence?
I'm trying to design a quasi-simple vertical axis wind turbine, and a coworker came up with this design to focus the wind as it reaches the turbine in a wind tunnel. He says that there's going to be ...
6
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4answers
428 views
Would a fish in a sealed ball swim normally?
This question led me to wonder whether swimming would be the same experience for a fish in a full, sealed ball as it is normally.
If the fish is about 7cm from the walls of the tank, a pressure wave ...
9
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3answers
545 views
Could a fish in a sealed ball, move the ball?
If you had a glass ball filled with water, completely sealed and containing a fish, could the fish move the ball?
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0answers
194 views
venturimeter and head in it [closed]
A venturimeter is to be fitted to a 250mm dia pipe in which the max flow rate is 7200l/min and the pressure head is 6m of water.What is the min dia of throat so that there is no negative head in it?
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7answers
530 views
Does the wind gust over the ocean?
It is easy to observe that on a windy day, the wind does not blow for several hours at constant speed, then gradually subside. Instead, on a time scale of seconds or tens of seconds, there are ...
1
vote
1answer
351 views
Kinetic energy loss when a rigid body falls into water
Assume you have a rigid body falling into the ocean at terminal velocity. Also assume that the rigid body does not break on impact. How could you figure out how much kinetic energy would be lost in ...
1
vote
1answer
1k views
“Troll physics”: Buoyancy for infinite power [duplicate]
Possible Duplicate:
What is the fallacy in this infinite motion machine?
Most of the "troll physics" images I can figure out, but this one has me stumped. What is broken about the following ...
3
votes
1answer
156 views
How can you tell a model explosion from the real thing?
Movies and TV shows frequently show buildings being bombed, cars blowing up, etc. Frequently these are really explosions of miniatures filmed up close.
Aside from the speed that the explosion ...
8
votes
4answers
312 views
Are smaller soap bubbles more accelerated by wind?
If you blow a bunch of soap bubbles outside, and a gust of wind hits them, will the bigger ones be more or less accelerated by the wind than the smaller ones?
Intuitively, and maybe from remembered ...
3
votes
2answers
281 views
Laws of fluid flow in porous medium
What are the equations that describe the flow of a fluid in a porous medium? Is there a variation of the Navier-Stokes equations?
I would like to model the flow of air through a sponge-like ...
11
votes
2answers
436 views
How to model/simulate pressures and flows in a network of pipes
I'm having a hard time finding information on how to model/simulate this. I attached a couple files, both of which show an example tank & pump network. It's just nonsense that I made up for this ...
7
votes
1answer
743 views
water flow in a sink
When one turns on the tap in the kitchen, a circle is observable in the water flowing in the sink. The circle is the boundary between laminar and turbulent flow of the water (maybe this is the wrong ...
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5answers
745 views
Is it possible for wind to break the sound barrier?
I understand that in nature wind would never get high enough, but I am just curious as to whether physics would allow this to occur or not.
7
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1answer
588 views
Pendulum with water dripping out
Consider a pendulum, consisting of a string of length $l$ tied to a ball of negligible mass and radius $r$. The bob is filled with water, which has density $d$, and the pendulum is given a small push ...
11
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7answers
1k views
Why there's a whirl when you drain the bathtub?
At first I thought it's because of Coriolis, but then someone told me that at the bathtub scale that's not the predominant force in this phenomenon.
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2answers
470 views
A water drop in a falling lift
Consider a lift, which is at rest in an homogeneous gravity field. There is a thin layer(with thickness $h$) of water on the floor of the lift. At some moment a single cable, supporting the lift, ...
4
votes
5answers
354 views
Tsunami dampening mechanisms
Encouraged by the zeitgeist let me ask the following:
Is it feasible (now or in the future) to build systems a certain distance of a vulnerable coastline which can serve to dampen a tsunami before it ...
3
votes
2answers
320 views
Mixed conductive and convective heat transfer
I want to make a finite element analysis of a cold airflow through warmer pipes. In particular I want to see how the pipes cool down and the air heats up, as it travels through the pipes. Wich are the ...
3
votes
1answer
1k views
How far will water squirt out from a hole in a can?
Say you have a bottle of water filled up to a height H. A small hole is drilled in its side at a height d, so that water squirts out. The squirting water travels in an arc as it falls, covering some ...
5
votes
2answers
477 views
Strange behavior and motion of bubbles in a glass of beer
Very unintuitive observation:
I pour myself a Guinness and the bubbles in my glass seem to move down toward the bottom of the glass instead of rising directly to the top of the glass as foam.
How ...
8
votes
2answers
751 views
The Galileo thermometer: why do the bubbles float in the middle of the tube?
If the water were uniform temperature, it would have uniform density, so a bubble should either be all the way at the top (if it's lighter than water) or all the way at the bottom (if heavier). But in ...
3
votes
2answers
602 views
Reynolds number, turbulence regime, and drag force
I am trying to model a system in which cubes of about 2 cm in size are floating in a circular water thank of about 30 cm in diameter. The cubes move around under the influence of the fluid flow ...
2
votes
2answers
769 views
Pressure vs wind speed, on a rectangular surface
How do I go about finding the pressure exerted on a rectangular surface in a free flowing air stream?
I wouldn't imagine that this is directly related to the airspeed / surface area, but have no idea ...
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0answers
226 views
Creating the proper suction
I'm a bit rusty on my fluid dynamics. I'm experimenting with creating my own leaf vacuum.
How would I determine how much suction a fan creates?
Bernoulli's equation would apply correct?
I would ...
12
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1answer
264 views
Why is there a breakdown in Kolmogorov scaling in turbulence?
Why is there a breakdown of Kolmogorov scaling in turbulence? What causes intermittency?
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1answer
148 views
What keeps the sugar suspended in the tea?
At room temperature....
How long will the sugar stay suspended once dissolved ?
What governs the rate of settling ?
What part does Brownian motion play ?
Sugar might be a bad example...please ...
5
votes
1answer
436 views
Viscosity/Entropy ratio and unitary evolution in quantum gravity
Calculations of the shear viscosity of the quark-gluon plasma (QGP), observed in heavy ions collisions, are performed via the AdS/CFT correspondence [ref1]. One finds that the shear viscosity of the ...
5
votes
1answer
508 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 ...
6
votes
2answers
279 views
Why is the answer to this diffusion example unintuitive?
Imagine a linear decrease in concentration from left to right. Using Fick's first law,
$J = -D \frac{d \psi}{d x}$
for all x, from left to right, we have the same flux amount because the decrease is ...
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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 ...
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vote
1answer
137 views
Time evolution of wave spectrum
A useful way of thinking (not only) oceanic waves is to consider them as a superimposition of linear modes: the elevation η of the sea surface is given by:
1: $\eta({\bf x}, t) = ...
8
votes
4answers
1k views
Water pressure in free fall
The increasing water pressure as you go deeper is generally explained in terms of the weight of the water column above the observation point pressing down. The question, then, is what would happen if ...
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2answers
348 views
Speed of sound in astrophysics
Why is the speed of sound given so much importance in Astrophysics? For example in gas outflow (and accretion) problems, we often calculate the sonic point (the point at which the outflow speed ...
5
votes
1answer
168 views
Resonance modes of a cubic box of water which we shake
I don't know hydrodynamics, but I wonder how one would compute resonance modes of a cubic box of water which we shake. I believe the waves would directly depend on the height of water and the width ...
0
votes
1answer
305 views
Given temperature, composition, column density, and radial velocity, can I find the bulk flow of a gas cloud?
We've got a hot star in the middle of a gas cloud. We point a spectrometer at the star, calculating the following attributes of our line of sight at the star through the cloud:
Total number of ...
5
votes
1answer
709 views
How to compute the speed of sound in relativistic hydrodynamic?
In Weinberg: Gravitation and Cosmology chapter 2.10 (Relativistic Hydrodynamics) the speed of sound is derived as
$v_s^2 = \left(\frac{\partial p}{\partial \rho}\right)$
and the equation of state ...
2
votes
2answers
160 views
Mixing of fluid in a rotating barrel
A barrel/drum with a diameter of 60cm is rotating at 20RPM to get a good mixing of the fluid contained (type thick oil).
At what RPM should a barrel of 30cm rotate to get the same mixing efficiency ...
4
votes
1answer
361 views
Common approximations for fluid outflow beyond Torricelli's law
Last month, a puzzle here in physics.stackexchange asked to calculate the dynamics of the outflow in a loose (over rails, no friction) tank using Torricelli's law as a simplification. The ...
