The quantitative study of how fluids (gases and liquids) move.
2
votes
0answers
23 views
Integral related to particle diffusion
In the context of particle diffusion, I am trying to understand the equations that describe Brownian motion as a macroscopic process.
Assume $N(x,t)$ is a number concentration and $D$ is a diffusion ...
-5
votes
0answers
24 views
A tank full of water has a small hole at its bottom [closed]
A tank full of water has a small hole at its bottom. If one forth of the tank is emptied in $t_1$ sec and remaining three fourth of the tank is emptied in $t_2$ sec, the ratio of $t_1/t_2$ is?
3
votes
1answer
21 views
In turbulence theory, what happens if i take space average of fluctuating part?
According to Reynolds decomposition, velocity field is split into two time average and fluctuating parts:
$$u_{({\bf x},t)}=\overline u_{(\bf x)}+u'_{({\bf x},t)}$$
we know that time average of ...
0
votes
0answers
15 views
simplification of bulk algorithms for surface fluxes
Im trying to calculate the surface heat fluxes from bulk algorithms following the methods defined in Renfrew et al., (2002)
A Comparison of Surface Layer and Surface Turbulent Flux Observations
...
9
votes
2answers
98 views
Ball jumping from water
Few days ago I played with ball(filled with air) in swimming pool. I observed interesting phenomenon.
When I released a ball from 3 meters depth the ball barely jumped above the water surface but ...
-4
votes
0answers
29 views
What Water Double Slit Experiment equation? [closed]
What is equation of double slit experiment through water?
i search but i didn't find it in fluid dynamic section.
what wikipedia link for double slit experiment through water?
4
votes
1answer
47 views
Fluids in thermodynamic equlibrium
I am reading about the Euler Equations of Fluid dynamics from
Leveque's numerical methods for conservation laws.
After introducing the mass, momentum and energy equations, some thermodynamic
...
0
votes
0answers
20 views
Outflow for fluid simulation based on “Stable Fluids”
I've implemented a fluid simulation based on the paper Stable Fluids.
It works quite well, except I would like to have the velocity at the "upper" edge just to outflow and not to re-enter on the ...
1
vote
1answer
61 views
Pressure in Bernoulli's equation
!
I've been reading an introductory physics textbook. It has a chapter on fluids which I'm finding quite confusing. Specifically, I don't understand the meaning of the pressure terms $P_0$ and $P_1$ ...
10
votes
1answer
139 views
How would you swim in inviscid water?
The viscosity of water creates drag on swimmer's body so its effect is to slow down the swimmer. However the viscosity seems to be essential for pushing the water backwards by the swimmer's arms and ...
1
vote
0answers
18 views
virtual air-surface temperature difference above a water body
I'm trying to work through the equations for the following paper:
http://onlinelibrary.wiley.com/doi/10.1029/2009JD012839/abstract
and am trying to understand the concept of virtual air temperature, ...
1
vote
0answers
34 views
Is this the reason solids suspended in turbulent fluids don't settle?
While I know (and can observe) that solids don't settle easily in a turbulent flow, I struggle with understanding why exactly this is the case. Here' my problem:
Conceptually, turbulence means high ...
0
votes
1answer
44 views
Navier-Stokes - Complete set under turbulent eddy viscosity hypothesis
I'm looking for the complete set (x,y,z component) of the Navier-Stoke equations under the Eddy Viscosity hypothesis to model turbulent fluid flow.
I found the following, but I have a really hard ...
0
votes
1answer
28 views
How do we measure mean part or time average of velocity field?
How do we measure mean part or time average of a (known) velocity field?
In other words, if I know velocity field how can I measure its time average or mean part?
What is time average in general?
1
vote
1answer
30 views
Why is pressure gradient assumed to be constant with respect to radius in the derivation of Poiseuille's Law?
Poiseuille's Law relies on the fact that velocity is not constant throughout a cross-section of the pipe (it is zero at the boundary due to the no-slip condition and maximum in the center). By ...
-6
votes
0answers
37 views
how the free falling height of an object on water tank related to generated wave height? [closed]
My research topic is on generation of tsunami waves on a water tank.
3
votes
1answer
80 views
What is the Coandă effect? How is it defined, and what causes it?
Can anybody explain to me the Coandă effect well? I am finding that many definitions and explanations conflict.
I am particularly confused about the following points regarding the Coandă effect:
...
-4
votes
0answers
53 views
Differential equation for 2d fluid dynamical problem [closed]
Let's say I have a source and a sink present anywhere on a finite 2-dimensional plane, and also both are at a respectable distance from each other.
Question
Could someone formulate a differential ...
3
votes
1answer
62 views
What are the limitations of Smoothed-Particle Hydrodynamics?
I've been excited by some of the possibilities of Smoothed-Particle Hydrodynamics (SPH). I have seen some very exciting demonstrations of their use in 3D graphics, but I am wondering how well the ...
1
vote
1answer
42 views
Power in hydraulic analogy
In hydraulic analogy one compares electrical circuits with water circuits. For the electric case the formula $P = U \cdot I$ for the electric power holds. The analogous formula for water flow would ...
9
votes
2answers
237 views
How does a sponge “suck” up water against gravity?
If I take a sponge and place it in a shallow dish of water (i.e. water level is lower than height of sponge), it absorbs water until the sponge is wet, including a portion of the sponge above the ...
1
vote
1answer
30 views
Acceleration of a steady line vortex
In a question, I have to find the acceleration of a fluid parcel in a steady line vortex. I am given that $u_\theta=\frac{A_0}{r}$. So for a steady line vortex, the parcels are following circular ...
1
vote
1answer
31 views
Lorentz force for electrically conducting fluid flow in homogeneous magnetic field
I am mathematician and have paper which models situation when homogeneous magnetic field is applied to moving electrically conducting fluid. There is such Lorentz force formula on which all the work ...
0
votes
1answer
47 views
Addes mass forces: can a force depend on acceleration?
My friend and I had a little discussion about added mass forces.
I always interpreted "F=ma" as a cause-effect relationship, so I find rather uneasy to accept that the cause can instantaneously ...
1
vote
1answer
47 views
How to calculate flow rate from given stream function
I am stuck on a homework question, all because I dozed off in class.
I understand what a stream function is but I don't know how to apply it to calculate the flow in pretty much anything.
Here's the ...
-1
votes
0answers
45 views
Finite differences method applied to potential flow [closed]
I've seen that there is a way to use the finite differences method, on a cartesian orthogonal grid, to perform calculations on potential flow about an obstacle without using the Neumann conditions, ...
3
votes
0answers
40 views
Modeling the formation of a stellar system and matter accretion
I am trying to figure out what do I need to know to properly simulate the creation of a solar system from a particle cloud with random distribution of hydrogen atoms.
Being more of a programming ...
3
votes
1answer
67 views
Can convection cells evolve in stably stratified fluid?
Assume stably stratified fluid but not in equilibrium, e.g. with non-constant temperature gradient for example. Can convection cells be present? Typical example of convection cells is Rayleigh–Bénard ...
6
votes
3answers
155 views
What about negative Pressure?
Here is something I see :
Let's say the ideal fluid(water here) of density $\rho$ is drawn from a source by a motor and thrown upwards with a velocity $v$. Now we take the power of motor be ...
8
votes
3answers
281 views
Is the meander ratio of a river $= \pi$?
To get from point $A$ to $B$, a river will take a path that is $\pi$ times longer than as the crow flies (I think this result is from Einstein). What is the proof of this, and how well does it hold ...
1
vote
0answers
28 views
How to find outflow pressure/force of air through a pipe
I have been trying to find the correct method for determining the outflow force resulting from a certain amount of air being forced into a pipe of a certain dimension. Essentially i'm trying to ...
0
votes
0answers
45 views
How fast could a football drop? [closed]
Suppose we have a perfect spherical football with d=22.5cm and m=420g. The football has a initial vertical speed of v(around 20m/s, not sure if it will cause a turbulence) and zero angular speed. If ...
0
votes
1answer
61 views
rate of flow out of a reservoir
A reservoir contains a fluid, and there is an aperture at the bottom through which the fluid flows out as shown in the illustration:
I understand that the rate of flow is based on at least these ...
4
votes
0answers
76 views
Existence and uniqueness of Stokes flow [migrated]
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
49 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 ...
2
votes
2answers
49 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?
8
votes
1answer
567 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 ...
6
votes
1answer
90 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
49 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
46 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
41 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
1answer
52 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
77 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
84 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
39 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
61 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
48 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
23 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 ...
4
votes
1answer
68 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 ...
3
votes
0answers
54 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.
...
