The quantitative study of how fluids (gases and liquids) move.
4
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1answer
61 views
Existence and uniqueness of Stokes flow
What are the solution existence and uniqueness conditions for Stokes' flow?
$$\nabla p = \mu \Delta \vec{u} + \vec{f}$$
$$\nabla \vec{u} = 0$$
Maybe you could also provide some articles or books ...
3
votes
1answer
37 views
Ducted or open fluid flow, which is best for aerodynamics and lift
I'm designing a copter and trying to decide if the propellers should be ducted or open axial flow. I've read some theory on ducted and open air flow but I can't find any where that compares the two. I ...
0
votes
1answer
31 views
How do we measure velocity field?
How do we measure velocity field u(r,t)?
i know that how to measure ordinary velocity. $v=\frac{dr}{dt}$
but what about velocity field?
what is difference between them?
7
votes
1answer
474 views
Why doesn't a bus blow due to internal pressure?
When one travels in a bus, if he's sitting at any window, he will feel that the air is coming inside. If someone is standing at the open door of the bus, he'll also feel that the air is coming ...
5
votes
0answers
65 views
Why is there no UV catastrophe (divergence) in turbulence?
I have just read that as the Reynolds number is increased, the separation of macroscopic and microscopic scales increases and that this also means that there is no UV catastrophy (or equivalently UV ...
4
votes
1answer
44 views
What is the minimum pressure difference for your ears to pop?
I'm assuming the answer to this largely varies from person to person. Assuming you could instantly change the pressure around your head by amount $\Delta p$, what is the minimum $\Delta p$ for your ...
1
vote
1answer
40 views
Distribution of pressure inside a capsule
How would pressure of an ideal gas be distributed over the inside of a capsule (a cylinder with semi-spheres on the ends)? What about the strain on the material? Is there a general formula for how ...
1
vote
2answers
32 views
Water draining from a height into the bottom of a reservoir
If I hang one 5 gal. Bucket directly above another, put a hole in the bottom of the upper bucket with a tube inserted just inside hanging all the way to the bottom of the lower bucket and fill the ...
0
votes
0answers
23 views
Absolute Viscosity of Water at certain temperatures
I just started my class on fluid mechanics. There's a problem that requires absolute viscosity $u$ of water at 25C. I looked up my table in the book and I only have it for water at 20C and 30C. I ...
1
vote
1answer
52 views
SHM of floating objects
If we consider an object undergoing who has an acceleration proportional to the displacement of the object, it is going simple harmonic motion.
In terms of Newton's second law, this is $$ -\dfrac k ...
3
votes
1answer
60 views
What does the Reynolds Number of a flow represent physically?
What does the Reynolds Number of a flow represent physically?
I am having trouble understanding the meaning and the utility of the Reynolds number for a certain flow, could someone please tell me how ...
0
votes
1answer
27 views
Water ripples and nonzero divergence
In 2-d, one ripple would mean the velocity of water particles move out radially forming a circular wavefront. The Navier Stokes equations say the divergence of velocity has to be zero, but this ...
0
votes
2answers
53 views
Pressure in fluids
Fluids exert hydrostatic pressure because their molecules hit each other or the immersed body . But why is that at a greater depth pressure is higher when molecules are the same .
Assume density of ...
3
votes
1answer
32 views
(How) Does A Vortex Speed Drainage?
When a sink drains it forms a vortex. Does that vortex speeds drainage. If yes, how does the vortex speed drainage?
The only relevant thing I could find was an expensive article and a science fair ...
1
vote
0answers
22 views
What is the relationship between complex time singularities and UV fixed points?
In this paper it is described how the turbulent kinetic energy spectrum and the flatness (a measure for intermittency) are governed by the position of the (dominant) singularities of the solutions of ...
3
votes
1answer
52 views
How can I understand a Vortex Tube and its efficiency?
A Vortex Tube takes a pressurized input stream, most typically of a gas, and creates two output streams with a temperature differential. Apparently, it has been described as a Maxwell's Demon.
Both ...
2
votes
0answers
38 views
Finding Surface Tension of water at certain Temperature and Pressure
So the question is:
Using the Young-Laplace Equation (if applicable), find the surface tension (dynes/cm) for water at 20
degrees Celsius with 2.5 psi. Round to the nearest tenth.
...
7
votes
1answer
55 views
Can Increasing the Turbulence Inside a Pipeline Economically Increase Flow?
"The velocity gradient in turbulent flows is steeper close to the wall and less steep in the center of the pipe than it is for laminar flows (Blatt p.97)."
Does this mean that some degree of ...
2
votes
1answer
85 views
Stress energy tensor of a perfect fluid and four-velocity
In the following demonstration, there is an error, but I cannot find where. (I explicitely put the $c^2$ to keep track of units).
We consider a metric $g_{\mu\nu}$ with a signature $(-, +, +, +)$ :
...
1
vote
1answer
43 views
What is Convective acceleration of flow velocity?
I know that $\frac {dv}{dt}=a$ is acceleration,
but:
what is convective acceleration of a flow velocity?
what is difference between $(v\cdot \nabla) v$ and $v\cdot (\nabla v)$, ?
0
votes
2answers
74 views
Will a helicoper which is hovering inside a closed box move with the box when we move it? [duplicate]
I got this micro helicopter to play with, you know that cheap double bladed ones you can find for $25 or so. Anyway last night I was on bed trying to sleep and I got this idea, what if we put the ...
2
votes
1answer
61 views
Sign crazyness on the stress energy tensor?
I would like to know on what depends the sign of the stress energy tensor in the following formula :
$T_{\mu\nu}=\pm(\rho c^2+P)u_{\mu}u_{\nu} \pm P g_{\mu\nu}$
In my case the metric is equal to ...
1
vote
1answer
42 views
Computational Fluid Dynamics methods
I have read some articles about the finite difference method on a cartesian orthogonal grid. I understand how it works when Dirichlet boundary conditions are used, or when Neumann boundary conditions ...
2
votes
0answers
33 views
Shock Rarefaction Interaction
I am interested to see/know if there exist analytical solutions for shock/rarefaction interaction. A rarefaction wave catches up from behind to a shock wave. The shock will decay and the motion will ...
0
votes
2answers
52 views
Are the hypotheses of the Bernoulli equation satisfied for a bird or airplane wing at low Mach number?
A previous question by David Zaslavsky was a request for a broad, "how things work" type of explanation of the lift of an airfoil. The answers given there are enlightening, but don't address a more ...
2
votes
1answer
51 views
I read a book saying bernoulli's flight equations didn't have as much impact on lift as most people think [duplicate]
I'm a computer scientist that likes to read about math and physics occasionally. A local author at a nearby aviation center brought bernoulli's flight equations into question.
It was clear enough ...
0
votes
1answer
83 views
Enginering question about F1 car
In formula F1 car, air coming infront of the car goes up with very high velocity as a result pressure difference is created which is very high from Bernoulli theorem.. The F1 car is very light so ...
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. ...
2
votes
1answer
91 views
What is Relativistic Navier-Stokes Equation Through Einstein Notation?
Navier-Stokes equation is non-relativistic, what is relativistic Navier-Stokes equation through Einstein notation?
0
votes
1answer
29 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 ...
1
vote
0answers
32 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.
...
6
votes
2answers
176 views
General procedure for solving fluid flow problems
Could someone help me devise a short series of steps for solving an arbitrary fluid flow problem? Often the most difficult part of these problems is just figuring out what path to take in solving ...
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.
2
votes
1answer
20 views
Application of plasma actuators for flow control of moving objects
I've recently been to a converence on plasma physics were, to my surprise, a lot of presentations were concerned with plasma actuator.
Could someone, preferably in the field, tell me how long people ...
6
votes
2answers
134 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 ...
0
votes
0answers
51 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
55 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 ...
10
votes
2answers
255 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
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 ...
6
votes
0answers
47 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 ...
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
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?
2
votes
1answer
101 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 ...
4
votes
2answers
118 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 ...
1
vote
0answers
93 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 ...
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 ...
6
votes
2answers
115 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 ...
1
vote
1answer
51 views
Force required to move a fluid out of piston at depth
I have a cylinder filled with water in it at the bottom of the ocean. Say 100 meters down. In this cylinder is a piston that moves up and down. Its job is to squish the water out the bottom of the ...
