The quantitative study of how fluids (gases and liquids) move.
4
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2answers
339 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 ...
9
votes
8answers
2k views
Why do ice cubes come out easier from top trays?
This is my "hey, I've noticed that too!" question for the week. If you stack two plastic ice cube trays with water in them in a freezer, the resulting ice cubes in the top tray will usually come out ...
2
votes
2answers
133 views
Hot Air Balloon and Buoyancy
This is a conceptual question in a solution I am trying to understand.
Problem statement:
I have a balloon with a volume of V $m^3$. The outside air temp is $K$ kelvin
and mass to lift is $m$ kg.
I ...
5
votes
2answers
250 views
Explanation that air drag is proportional to speed or square speed?
A falling object with no initial velocity with mass $m$ is influenced by a gravitational force $g$ and the drag (air resistance) which is proportional to the object's speed. By Newton´s laws this can ...
2
votes
1answer
54 views
Work done by gravity on Water
Now according to me we would see change in potential energy of system and equate it to the work done by gravity.
But when we see this the first column lowers by $H/2$ and right one rises by $H/2$ ...
0
votes
0answers
25 views
how to explain the upright force for the plane? [duplicate]
I remember in the high school physics, my teacher told us that the design of the plane wing is because we want the air above the wing flowing faster than the air flowing below so the pressure above ...
2
votes
5answers
148 views
How does an aeroplane maintain balance during maneuvers?
I understand the principle behind flight, how the lift is generated etc. What I don't understand is when there are maneuvers made where the plane flies such that the wings are in vertical plane, how ...
1
vote
1answer
57 views
Query about Bernoulli's principle
We know that the lower atmosphere has high pressure and as we go up, the pressure decreases, if it's so then why doesn't all gases fly up into the upper atmosphere from the lower following Bernoulli's ...
16
votes
2answers
239 views
Stripeless cleaning of windows
Cross post: http://chemistry.stackexchange.com/q/4377/22
Last week I was discussing with a friend how we thought the stripeless cleaning of windows is achieved when using a cleaner like Windex ...
3
votes
1answer
144 views
Rayleigh-Benard Convection
I found this nice paper about RB convection. However I am confused by what is going on page 6. In particular why we are suddenly using Helmholtz equation to find spatially periodic solutions. Aren't ...
1
vote
0answers
46 views
Physical interpretation of an intermittency definition
A random function $v(t)$ is said to be intermittent at small scales of its "Flatness" $F$, given as
$$
F(\Omega) = \frac{\langle (v_{\Omega}^{>}(t))^4\rangle}{\langle ...
3
votes
3answers
91 views
Spinning liquid to create a centrifuge effect
I'm in the business of purifying used cooking oil. Normally, I heat the oil up and let it settle for a couple of days. Water and solids settle to the bottom and cleaner oil remains on top. I'm trying ...
32
votes
10answers
4k views
Why does dust stick to rotating fan propeller?
Why does dust stick to rotating fan propeller?
Intuitively, most people (including I) think of the dust will not stick to rotating fan propellers.
EDIT 1:
Thank you for the great explanations. I am ...
0
votes
0answers
47 views
Air flow in tube with smaller perforated holes balance
Given: I have a $1.5$ diameter tube that I'm pushing air through that has perforated holes along its length, and the far end is closed. Air leaves 10 perforated holes to atmosphere. Temperature is ...
6
votes
1answer
120 views
Could the Bernoulli effect be causing my ceiling to come down?
Very 'applied' question, but I have nowhere else to turn, so I'm asking the physics experts here: I have a carport whose ceiling is made of very lightweight paneling. I've had several times now that ...
1
vote
0answers
22 views
blood fluidics - can you determine the force exerted on a bound red blood cell under shear stress?
Is it possible to calculate the force exerted on a bound, infected red blood cell under various shear stresses? The strength of an adhesive interaction is normally measured by SPR or AFM, however ...
1
vote
0answers
29 views
where to find sample fluid stirring data?
I want to find some force data for fluid stirring. Originally I intended to record the data using my force sensor, but it doesn't have the resolution to read stirring force for Newtonian fluid.
...
3
votes
2answers
88 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 ...
4
votes
1answer
170 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 ...
11
votes
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.
2
votes
1answer
106 views
Is it wrong to associate non-isotropic flow high with Reynolds-Number and is there a better metric?
IT is often stated the flow with high Re is not isotropic, meaning there is no uniform or dominant direction of the flow. But this seems wrong to me - -while there's certainly cases where no dominant ...
1
vote
1answer
88 views
Why does tea rises in the pot but water don't?
I was wondering when I boil water in a pot it only shakes too much while boiling. But I could not figure out why tea rises in the pot when we boil it. it is also a liquid but it starts rising up till ...
4
votes
2answers
104 views
Best shape to reduce the splash of a droplet?
Our coffee machine catches the last couple of droplets, after your cup is removed on a shape to reduce plash of the coffee droplets.
These shapes are placed inside the spill reservoir.
The shape ...
2
votes
0answers
96 views
Conformal symmetry of Navier-Stokes?
This question is in reference to the paper arXiv:0810.1545
Can someone help understand this scaling argument and the proof(?) that there is a conformal symmetry in Navier-Stoke's equation? (..am I ...
2
votes
0answers
131 views
How to calculate the Darcy-Weissbach friction factor for shear thinning laminar flow in a pipe?
The Darcy-Weissbach friction factor for laminar flow would be $\frac{64}{Re}$
Now, having a shear thinning (non-newtonian) fluid where the viscosity is not constant how do I arrive at $Re$?
To know ...
0
votes
1answer
62 views
Can anyone explain what a superleak is?
In the context of Helium can anyone explain what a superleak is and why it could be useful?
4
votes
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 ...
1
vote
0answers
73 views
Wall pressure of a fluid flow in a pipe of variable radius
Using all cylindrical coordinates, pipe with z-axis vertically upward and radius of $r = G(z)$, flow is incompressible, inviscid and steady, Using appropriate boundary conditions I want to find the ...
1
vote
1answer
127 views
how to determine if a vortex is laminar or turbulent
In a cylindrical chamber with a high diameter-to-height ratio; a fluid is tangentially injected. there is an axial exit to the cylinder.
how do I determine if the vortex so formed is laminar or ...
6
votes
1answer
179 views
Gravity duals to Navier Stokes and interpretation of non linear contributions
I have been reading the paper The Incompressible Non-Relativistic Navier-Stokes Equation from Gravity. In it they state,
"An instability, if it occurs, must necessarily break a symmetry ...
...
9
votes
3answers
150 views
What does the quantification of causes and effect look like, for clouds in offshore wind turbine wakes?
At Horns Rev windfarm off the coast of Denmark, sometimes in winter, clouds appears in the wake of the turbines. I've only seen photos of the phenomenon when the wind direction is exactly aligned with ...
29
votes
8answers
9k views
Why does the atmosphere rotate along with the earth?
I was reading somewhere about a really cheap way of travelling: using balloons to get ourselves away from the surface of the earth. The idea held that because the earth rotates, we should be able to ...
5
votes
1answer
160 views
Drag on a spinning ball in fluid
I am a physics newbie (high school level) and I am wondering what happens when a spherical object is spinning on the spot in a bunch of gas (no gravity here, just an imaginary physics sandbox).
Am I ...
0
votes
0answers
134 views
pressure loss in a syringe
I'm currently working on a problem which is really giving me some issues.
The problem concerns the force required to expel water from a syringe. We have a 20ml syringe (which is $2\times10^{-5}$ ...
2
votes
2answers
50 views
Flux Over a Surface
I am teaching a multivariable calculus course and we are starting to go over surface integrals. I am a math professor with little knowledge of physics. At one point the book discusses fluid flow. ...
0
votes
1answer
57 views
Buoyancy fluxes in a stratififed fluid and units
I am calculating the buoyancy flux (B) for a stratified fluid as follows:
where g = 9.81 m/s; alpha = 1.6 x10^{-5} + 9.6 x10^{-6} x (20 degC); S = 100 Wm^{-2}, p0 = 1000 kg/m3, and Cpw is the ...
1
vote
2answers
151 views
Whirlpools and Tornados
This may not be a great question. But whenever you drain water, a small whirlpool happens, obviously. This got me thinking...
Can we model tornados with this effect, would it even be beneficial?
17
votes
3answers
793 views
Have we figured out how to analyze turbulent fluids?
I was surprised to read that we don't know how to analyze turbulent fluids. On page 3-9 of The Feynman Lectures on Physics (Volume One), Feynman writes:
Finally, there is a physical problem that ...
1
vote
1answer
153 views
Proof that flux through a surface is independent of the inner objects' arrangement
$$\Phi=\iint_{\partial V}\mathbf{g} \cdot d \mathbf{A}=-4 \pi G M$$
Essentially, why is $\Phi$ independent of the distribution of mass inside the surface $\partial V$, and the shape of surface ...
5
votes
2answers
84 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 ...
1
vote
1answer
378 views
Determine viscosity using falling sphere (Stokes Law, Ladenburg correction)
Introduction
I am trying to determine the viscosity of a fluid. Therefore, I let a sphere of known mass m and radius r fall ...
1
vote
1answer
129 views
Velocity required for Horizontal Rain
Related to my previous question - Change in appearance of liquid drop due to gravity...
Ok, I think we all have noticed this practical phenomena (a kind of illusion though)... During rain (while ...
4
votes
2answers
311 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 ...
2
votes
1answer
92 views
Bernoulli's theorem: $\frac{p}{\rho}+\frac{1}{2}u^2+\phi$ is constant along a streamline
I am trying to understand the Bernoulli's theorem:
$\frac{p}{\rho}+\frac{1}{2}u^2+\phi$ is a constant along a streamline
I got that:
$\frac{\partial u}{\partial t}$ + ($\nabla \times u)\times u$ ...
3
votes
2answers
109 views
Pumping water from a closed column. Will the column get empty or just circualte?
As a picture is worth a thousand words, here is my problem:
It is a closed water column with a bit of air in the top section.
If I run the pump and make the water flow from IN to OUT,
Will the ...
1
vote
2answers
60 views
Membrane that allows liquid to pass only when forced under pressure
Is it possible to have a membrane that will not let a liquid through it at normal pressures due to gravity, but pass that liquid when substantially pressurised?
For instance, a few inches of water ...
0
votes
1answer
84 views
What does Euler equation mean?
In order to prove the Bernoulli’s principle ($\frac{p}{\rho} + \frac{1}{2}u^2+\phi = constant$ ), I have to use the Euler equation: $\frac{Du}{Dt} = -\frac{1}{\rho}\nabla p + g$.
I know how to prove ...
2
votes
0answers
78 views
Difference between a Fixed Point and a Limit Point in implementations of the Renormalization Group (RNG) in Large Eddy Simulation (LES) model
In the introduction of this paper, it is explained that and how the application of a dynamic subrid scale model for turbulence into a large eddy simulation (LES) model corresponds to doing one ...
2
votes
1answer
133 views
1
vote
1answer
230 views
Wave propagation in an incompressible flow
Incompressible approximation of fluid flow is usually known to be lame in modeling the propagation of any disturbance in it, predicting a speed equal to infinity for the propagation of the ...
