The quantitative study of how fluids (gases and liquids) move.
2
votes
1answer
92 views
Showing symmetry of the stress tensor by applying divergence theorem to $\int\int_{\delta V(t)} \vec{x}\times \vec{t} dS$
I'm currently working through the symmetry of the stress tensor, in relation to viscous flow. I am looking at this by examining the conservation of angular momentum equation for a material volume ...
3
votes
1answer
66 views
Equidistant coffee rings in a mug: pinning boundaries coupled with migration of solute or just sip volume?
I understand that you get coffee rings on a table as a result of solute migration (solutocapillarity) towards the pinning of the circumference of the coffee ring [Deegan et al.].
Below is an ...
1
vote
0answers
21 views
Books describing motion of objects in fluid [closed]
I'm looking for any resources that would help me model the behavior of objects moving in fluid. My end goal is to be able to describe the motion of irregularly shaped objects in a river environment. ...
0
votes
1answer
30 views
Additional boundary conditions for inclined flow?
I am solving an inclined flow problem, and am stuck. The problem is to find the volumetric flow rate of inclined flow in a square channel. Once I have the velocity profile, I can just integrate over ...
38
votes
2answers
576 views
Analog Hawking radiation
I am confused by most discussions of analog
Hawking radiation in fluids (see, for example,
the recent experimental result of Weinfurtner et
al. Phys. Rev. Lett. 106, 021302 (2011), ...
1
vote
1answer
126 views
Validity of the Multi-Species Navier-Stokes Equations for real gases
I'm wondering what are the validity limits of Multi-Species Navier-Stokes equations. I'm aware of the limit for rarefied gases. But is there any new limit that arises in the context of real gases?
I ...
1
vote
0answers
35 views
What is a good reynolds number for this process?
I’m trying to convince my boss that the mixers we are using are too much. I’m trying to prove that we are over-mixing our product. Our product is ink…just your basic ink found in your printer at home. ...
1
vote
0answers
15 views
CMB anisotropies and tightly coupled limit
Sorry if this is a technical question. I am studying the origin of CMB anisotropies and the tightly coupled limit of the Boltzmann equations. We have a fluid composed of ionized electrons and photons.
...
16
votes
4answers
363 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
461 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
13 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
136 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
1answer
210 views
Calculating Reynolds number for a viscous droplet
I'm trying to develop a very basic scaling law/unit analysis for viscous droplet formation, and I'd like to get some rough numerical values of the Reynolds number to play with. To be specific, I'm ...
4
votes
3answers
327 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 ...
4
votes
1answer
140 views
Lagrangian Coordinates in Fluid Flow
I apologize if this is not the right place to ask this question:
I am currently reading a paper by Y. Brenier, where for the fluid flow he introduces a Lagrangian label $a$ instead of the vertical ...
10
votes
2answers
261 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
50 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?
1
vote
1answer
285 views
Archimedes principle and specific gravity
A physical balance measures the gravitational mass of a body. I conducted an experiment to find out the specific gravity of a bob. I first measured the mass of the bob in air, and then in water. The ...
0
votes
2answers
107 views
The viscous force between the layers of liquid is same, then why there is variation in the velocities of its layers?
I have learned in my textbook that when the liquid flows the bottom layer of the liquid never moves because of friction, but the upper layers move with increasing velocities how it is possible if the ...
1
vote
1answer
848 views
Dimensional Analysis: Buckingham Pi Theorem
I am studying for a fluids quiz and I am having a few problems relating to dimensional analysis but for the time being fundamentally I have a problem selecting the repeating variables. Like does ...
0
votes
0answers
52 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 ...
4
votes
2answers
59 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 ...
2
votes
1answer
80 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
368 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
546 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
122 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
48 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 ...
36
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
46 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
103 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
527 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
96 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
83 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
167 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
65 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
250 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
142 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
107 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
118 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
178 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
34 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
92 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
95 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
110 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
113 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
288 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
62 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
434 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 ...
6
votes
2answers
147 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 ...
