The quantitative study of how fluids (gases and liquids) move.
16
votes
4answers
371 views
Why does the fundamental mode of a recorder disappear when you blow harder?
I have a simple recorder, like this:
When I cover all the holes and blow gently, it blows at about 550 Hz, but when I blow more forcefully, it jumps an octave and blows 1100 Hz.
What's the ...
1
vote
3answers
651 views
What's the surface area of a liquid? How does evaporation increase if the surface area of a liquid is increased?
Wikipedia says that a substance that has a larger surface area will evaporate faster, as there are more surface molecules that are able to escape. I think the rate of evaporation should decrease as ...
0
votes
0answers
14 views
What type of constraint is the homogeneity of a fluid?
Suppose we have a homogeneous fluid (may or may not have viscosity). Is the constraint due to homogeneity a holonomic constraint? Thanks.
6
votes
2answers
156 views
Hydrostatic pressure on a teapot spout
The phenomenon where water flows on the outside side of a teapot spout is named "The teapot effect", and occurs due to a difference in pressure between water and the atmosphere. Consider the image of ...
4
votes
3answers
398 views
A fly in an accelerating car
A fly is flying around in a car, the fly never touches any surface in the car only fly’s around in the air inside the car. The car accelerates. does the fly slam in to the rear window. or does the fly ...
10
votes
2answers
273 views
Can vorticity be destroyed?
I have a professor that is fond of saying that vorticity cannot be destroyed. I see how this is true for inviscid flows, but is this also true for viscous flow? The vorticity equation is shown below ...
2
votes
0answers
51 views
Seashell occurrance
Sometimes, sea shells accumulate on the sea shore, but sometimes they will instead be dragged back out to sea. What are the main physical factors that determine which of these things will happen?
0
votes
0answers
59 views
Equilibrium of a sphere in a water tank
A rigid sphere of radius $R_S$ made from a material with specific gravity $SG_s$ is completely
submerged in a tank of water with radius $R_t$ and initial depth $L$ as shown in the figure
The ...
2
votes
1answer
88 views
Perfect fluids in cosmology?
In cosmology, it is often assumed that the equation of state of a cosmological fluid is of the form $p=w\rho$. Why is this? Is it the equation of a perfect fluid?
Why does $w=0$ for matter $1/3$ for ...
19
votes
3answers
388 views
How much information about the scale of a waterfall can be obtained from its sound?
Is it possible to constrain the height, volume flow, or distance of a waterfall from the quantitative analysis of a high-quality recording of its sound?
As an aside, the simulated sounds of fluid ...
4
votes
2answers
550 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
2answers
141 views
Physics behind the flow of gas coming out of a balloon
I'm working with stratospheric balloons (latex ones) and I want to put a valve on it so it can float for a longer time. I'm trying to define which valve I should use, which demands I estimate the flow ...
6
votes
0answers
49 views
Undergrad project advice [closed]
I am presently in my senior year and I am considering fluid mechanics for my thesis.
What area of research of fluid mechanics which is purely analytical and very mathematical since I am an applied ...
38
votes
11answers
4k views
How long a straw could Superman use?
To suck water through a straw, you create a partial vacuum in your lungs. Water rises through the straw until the pressure in the straw at the water level equals atmospheric pressure. This ...
2
votes
0answers
52 views
Robot controling pouring process from a bottle
I need to solve a problem within mechanic of fluids for a part of my thesis. Robot will pick up a bottle of beer, cola, julebrus or any other kind of beverage. And then it has to bring it to the glass ...
2
votes
1answer
148 views
Drinking juice through a straw
Why we are able to suck more drink through a larger diameter straw than a smaller diameter straw if $p_1 v_1 = p_2 v_2 = Q$ as per Bernoulli's Principle. The pressure difference I create in mouth ...
3
votes
2answers
547 views
Is the wind's force on a stationary object proportional to $v^2$?
I am on a boat docked at Cape Charles, VA, about 30 or 40 miles from the center of Hurricane Irene. This understandably got me thinking about the force of wind on the boat. Since air friction is ...
1
vote
0answers
98 views
2-D Turbulence - how does it look like?
Consider parallel flow in the X direction over a 2D semi infinite flat plate. If turbulence is 2-D, in which axes should we expect the vortices to form.
Also, are there any experimental/visualization ...
6
votes
1answer
90 views
In a column of rising hot air, is the velocity higher at the top?
Since the movement of the air is induced by buoyancy, i. e. there's a constant force acting on the air, so I would expect the velocity to increase during ascent, much like an object falling down due ...
7
votes
3answers
176 views
How do I intuit viscosity in a rotating fluid?
Suppose I have two plates with a viscous fluid in between. I slide them in the same direction (a direction in their own plane), one at $5 \,\text{m/s}$ and the other at $6 \,\text{m/s}$. Due to the ...
1
vote
1answer
69 views
Explanation for the next steps of chaplygin dipole
this post is the Chaplygin dipole, it's an interesting issue.
Can someone explain me these steps in other words please? any Explanation of any step will help me, I hope that together I will ...
8
votes
1answer
259 views
Why does a transformation to a rotating reference frame NOT break temporal scale invariance?
Naively, I thought that transforming a scale invariant equation (such as the Navier-Stokes equations for example) to a rotating reference frame (for example the rotating earth) would break the ...
5
votes
1answer
160 views
Why do air bubbles stick to the side of plastic tubing?
I'm watching water with air bubbles flow through transparent plastic tubing. The inner diameter is a few mm. Bubbles typically are the same diameter as the tubing, with length about the same or up ...
0
votes
3answers
122 views
Navier-Stokes system
I have to study this system which name is Navier-Stokes. Can you explain please what means that $p$, $u$ and $(u \cdot \nabla)u$. What represents in reality? Tell me please, how should I read the ...
6
votes
2answers
138 views
Could some design of a propeller be used in both air and water?
Propellers in water are smaller in diameter. They also move more slowly. On the other hand, aircraft propellers are larger in diameter, have narrower blades and operate at very high speeds. An ...
0
votes
0answers
33 views
Curls in water taken in a liquid [duplicate]
Consider a beaker having a hole at the bottom at its geometric centre is connected to a pipe which is closed initially. Water is filled when the pipe is opened I saw curls are being formed. Why they ...
2
votes
1answer
197 views
How much effect does the Bernoulli effect have on lift?
I understand that the Bernoulli effect is a flawed explanation for the cause of lift, and does not cause much at all, but how much?
Is there any experimental data on the force caused by the ...
1
vote
0answers
36 views
What temperatures can be reached in an air-to-air thermocompressor nozzle and why?
People are generally of the opinion that the boiler injector cannot be redesigned to run on air. In other words, an air-to-air thermocompressor that puts fresh air into a tank without a mechanical ...
1
vote
1answer
115 views
Does gravity affects temperature reading of a mercury thermometer?
I remember when I was in primary school, the science teacher put me in charge of a mercury thermometer. I do not quite understand the mechanics behind except that mercury expands when it is hot and ...
1
vote
1answer
122 views
Concerning drag on a flow past a cylinder
I am wondering about the drag coefficient for a flow past a cylinder. I am reading this article.
I understand why the drag is high to begin with (point 2), when the boundary layer separates and the ...
0
votes
2answers
122 views
Will this type of engine produce thrust?
I was wondering that if I create a engine as shown below in the image will it produce any kind of thrust or it is a complete junk?
2
votes
2answers
132 views
Whats the anti-torque mechanism in horizontal take-off aircraft?
In most helicopters there is the anti-torque tail rotor to prevent the body from spinning in the opposite direction to the main rotor.
What's the equivalent mechanism in horizontal takeoff single ...
3
votes
1answer
333 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?
1
vote
1answer
65 views
Calculating the dimensional wall-normal coordinate for a self-similar compressible boundary layer using Levy-Lees transformation
How can I convert my self-similar boundary layer solution that is a function of the nondimensional wall-normal coordinate $\eta$ to be a function of dimensional $y$? For instance, if I determine from ...
2
votes
3answers
474 views
Apparent paradox in equation of continuity
Equation of continuity says us that if we insert some fluid in a tube, the same amount of fluid will come out from the other end. If we make a small hole in a hose pipe, water will come out with a ...
7
votes
2answers
159 views
Why water in the sink follow a curved path?
When you fill the sink with water and then allow the water to be drained, the water forms a vortex.. And then it starts to follow a curved path downwards by effects of gravity..
Why this phenomena ...
4
votes
2answers
340 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
193 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 ...
2
votes
1answer
61 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
4answers
163 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
63 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
249 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
149 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
53 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
97 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
58 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
121 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 ...
