The quantitative study of how fluids (gases and liquids) move.

learn more… | top users | synonyms (1)

1
vote
0answers
26 views

What is the viscous force acting on a cube?

I'm aware of the viscous drag formulae to calculate the drag force acting on a moving sphere inside a viscous fluid. But how do you improve the formulae to get the force acting on a cube with side ...
3
votes
1answer
75 views

What's the difference between “Ohmic dissipation”, “Joule heating”, “ion drag” and “resistive heating”?

The following terms are sometimes used to refer to ... more or less ... the same thing by different people and in different contexts (electronic circuits vs. plasma physics, etc.): Ohmic ...
1
vote
1answer
20 views

Bubbly Flow and two phase flow modelling

When we pour vine or some other drink why bubbles move upward and what law they follow or what is the law that describe that motion? One other question If we consider a simple two phase flow between ...
0
votes
1answer
43 views

Fluids in motion and pressure

We are taught in the lessons of fluid mechanics that for an ideal non compressible and non viscous fluid $at-rest$, the pressure at any point within the fluid is independent of the direction. But I ...
2
votes
1answer
43 views

Unsmooth behavior of water waves

I happened to come across this rather interesting picture of a very deformed (or perhaps intricate) wave. The structure looks like it illustrates a superposition of multiple waveforms, as intuitively ...
2
votes
2answers
73 views

Why is the solution to the Blasius boundary layer problem self-similar?

In every course or textbook that I encountered so far, the authors transform the Navier-Stokes equations of the Blasius boundary layer problem into the Blasius ODE. The problem with many of those ...
2
votes
2answers
46 views

What is the physical meaning of $v\times n$?

What is the physical meaning of $v\times n$, where $v$ is a velocity vector and and $n$ is a unit normal vector of a interface? Why at the free surface between two fluids, $$v^{(1)}\times ...
0
votes
1answer
49 views

Why does plugging a hole in an airplane's fuselage result in a huge (10x) atmospheric pressure spike?

While reading about uncontrolled decompression, I came across one famous airline incident, Aloha Airlines Flight 243, where the article I was reading discussed a 1-square-foot hole created in the ...
0
votes
1answer
88 views

What are premultiplied energy spectra?

When speaking about turbulence in fluid mechanics many times authors speak about "premultiplied energy spectra" but they never explain what really it is. I have searched for a definition but I did not ...
0
votes
1answer
48 views

How to make a structure of which water flows out at a constant rate? [closed]

Is there any way to make a structure of which water flows out of at a constant rate? Any way could be used to build the structure, including 3D printing.
1
vote
2answers
48 views

Using fluid mechanics to show that force is directly proportional to velocity

So I am writing a paper about viscous dampers in harmonic oscilators, however I was looking at some old fluid mechanic notes and I thought I had come across what I needed although I have gotten stuck. ...
2
votes
3answers
229 views

Distance traveled by a water jet

I helped my kid in a science fair project, where we punctured holes in a water bottle at various heights and then measured the distance traveled by the water jets before they hit the ground. The ...
4
votes
2answers
91 views

Does the definition of compressibility depend on the frame of reference?

According to many authors, a fluid is defined to be incompressible if the material derivative of the density $\frac{D\rho}{Dt}$ is zero, that is to say, that in an frame of reference following the ...
2
votes
1answer
98 views

Boat Hull Drag in Shallow Water

I paddle several different types of small craft in the ocean and bays near my home. One phenomenon I've observed is beyond my understanding of drag on a narrow displacement hull. When paddling in ...
0
votes
1answer
35 views

Monoatomic fluids and free space around atoms

In monoatomic fluids the atoms can move quite freely around each other. Is there any thermodynamic/statistical mechanic equation how much free space there is between the atoms? This has to be ...
1
vote
2answers
89 views

Do rotating non-circular projectiles also experience Magnus lift?

The Magnus effect has been studied on spherical projectiles such as golf balls, tennis balls, and soccer balls. The backspin of a golf ball leads to Magnus lift that opposes gravity, thus allowing the ...
3
votes
1answer
93 views

Is Archimedes' principle valid with moving objects?

I was solving a classic application of Archimedes' principle: a body partially submerged that is made to oscillate vertically and perform a simple harmonic oscillations. The equations turn out to be ...
2
votes
0answers
78 views

Why is the water in a cup not inclined (opposite the cup) when the plane takes a turn?

When a aircraft takes a turn: Why is the water in a cup not inclined (opposite the cup)?
0
votes
2answers
84 views

What is the pressure of falling water?

Imagine a breaking wave 10m high. The wave breaks onto a beach. What is the maximum pressure created by the wave on the beach, ignoring effects such as might be cause by air?
0
votes
1answer
31 views

Reference for passive scalar

I would like to learn about turbulence of a scalar advected by a random velocity field. I know that this problem can be solved analytically and that the statistics of the scalar field are ...
0
votes
1answer
21 views

the different settling speed of two solid particles in fluid

In a container full of fluid A, which can be water or oil, I have two solid particles, both of which are of the same material. These two particles are of different size. One is bigger than the other ...
-3
votes
2answers
101 views

Ice when melted at zero gravity [closed]

I wish to know the behavior of ice at zero gravity, how ice will behave when melted at g=0? Thanks
1
vote
2answers
90 views

How to increase flow rate? [closed]

I am coming up with ideas of how to increase grain (corn, soybeans etc,) flow in a tube. My first idea is to have spiral ribs inside of the tube to create a vortex effect that will allow the grain to ...
7
votes
0answers
160 views

Could Navier-Stokes equation be derived directly from Boltzmann equation?

I know how to derive Navier-Stokes equations from Boltzmann equation in case where bulk and viscosity coefficients are set to zero. I need only multiply it on momentum and to integrate it over ...
7
votes
3answers
625 views

Why does the lake surface appear darker in some areas?

What causes the surface of the lake to appear darker in some places? Firstly, I know that it's not fishes that cause it. Secondly, the dark surfaces move from time to time and thus are not ...
3
votes
2answers
79 views

Patterns in laminar flow of tap water

This is a simple experiment that anyone can do at home. Open your tap so that the water maintains a laminar flow, and the cross section of flow is considerably thin. Place your finger 3-4 cm below the ...
4
votes
2answers
281 views

Fluid flow: Force acting on the fluid and the Navier-Stokes equation

Consider a one dimensional fluid flow in a rectangular tube. Typical streams are the poiseuille streams. Consider the case in wich we apply a force on the fluid. The Navier-Stokes equation (for ...
11
votes
1answer
211 views

Equation derivation for skipping rocks

oWhy can rocks skip over water? For instance, if you conduct an experiment where you drop both rocks from the same height, but give one considerable acceleration in the x direction, one will fall in ...
1
vote
0answers
34 views

Are there any in depth superfluid mechanic analyses of spacetime?

Has there been much work done that treats particles as vortexes in a fluid, or dark matter as bubbles in this fluid (bending space in the same way massive particles (vortexes) are observed to do, but ...
1
vote
2answers
52 views

Does air density influence a football player's ability to “bend” the ball?

Whilst reading an article on nasa.gov, there was a claim that I found interesting: At higher altitudes, the density r is lower producing a larger radius of curvature and a straighter path. The ...
2
votes
0answers
27 views

Fluid approximation for inflaton?

In cosmology there is a widely used fluid approximation which applies when the mean free path is very small compared to the scale of observation and then all the properties of stress energy tensor can ...
1
vote
0answers
55 views

Why do clouds not fall? [duplicate]

The density difference between the clouds and the atmosphere favours the clouds to fall. Why don't they?
0
votes
1answer
33 views

Calculate the pressure required to stop a pipette (or pipe) from dripping [closed]

Suppose that I have a pipette with a length of 10 cm that is filled with water, with a diameter of 1 cm. If it is held vertically, how would I calculate the pressure required to stop any water from ...
1
vote
1answer
38 views

Change in radius of a charged bubble

I was thinking about what'd happen to the radius of a bubble, if a charge is uniformly distributed over it. At the beginning, I thought that the bubble would expand, for sure, because of the ...
11
votes
2answers
222 views

Why pouring milk from a height makes a chain shape? [duplicate]

I have noticed a chain-like shape when milk is poured from a height into a cup. Actually the chain pattern repeats itself after some distance and again till it reaches the milk in the cup. Any ...
1
vote
1answer
62 views

Why Benard cells are usually hexagonal?

Solution of equations of convection (hydrodynamics equations in Boussinesq approximation) involves existence of convective cells, so-called Benard cells. They are represented by superposition of ...
2
votes
1answer
47 views

Is, in terms of sound, pouring water in a bottle the analogous of blowing into it?

When we pour some liquid in a closed container, for instance a jar or a bottle, we usually hear two (acoustical) noises: one is the classical turbulent (I guess white) noise, that in my view is ...
0
votes
1answer
35 views

Amount of unknown parameters in compressible Euler equations

I'm looking at this page for the compressible Euler equations. To me it seems, in the 1-dimensional case, there should be 3 unknowns: density, velocity, and pressure. This is because the energy $E$ ...
1
vote
0answers
22 views

The free surface of the wave is a material surface

If we define the free surface by: $F(x,y,t)=y-h(x,t)=0$ Then for this to be a material surface $\frac{DF}{Dt}=0$ on $y=h(x,t)$ However on $y=h(x,t)$, $F=0$, so doesn't this just imply ...
1
vote
0answers
149 views

Static pressure in relation to CFM

I’ve scoured the internet in search of an answer to no avail, so it’s time to ask the experts! My background is more Chemistry and Biology, not Physics, or specifically fluid dynamics, so bear with ...
0
votes
1answer
91 views

Metric inside a sphere of uniform density?

Is an exact solution to Einstein's Field Equations known for the interior of a sphere of uniform density (to approximate a star or planet, for example?)
0
votes
1answer
64 views

Rate of evaporation of water with mass loss at set temperature and pressure

I have a cylindrical tank with an 'm' amount of water in it. The tank is sealed except through an exhaust with a fan that keeps a lower than atmospheric pressure (but not vacuum) inside the tank. The ...
1
vote
2answers
86 views

Given airplane mass, velocity of air under wing, and a wing area, find velocity of air over wing

I attempted to solve this problem as a tutor for a student and struggled, but want to be convince the professor didn't provide enough information. The problem is essentially: We wish to maintain a ...
0
votes
2answers
56 views

Eulerian mass conservation on a stream line to Lagrangian mass conservation

if the density of a fluid particle is conserved on a streamline, $$\frac{d\rho}{dt}=0.$$ Why does this mean $$\frac{\partial \rho}{\partial t}+(\mathbf{v}\cdot\nabla)\rho=0$$ is true everywhere? Why ...
0
votes
0answers
29 views

How can a rotating cylinder produce lift? [duplicate]

In the air, the velocity and angular momentum that causes a force against gravity is lift. How can a rotating cylinder make lift with angular momentum?
0
votes
1answer
32 views

Can the fluid volume in a control volume change over time?

For a control volume, am I right in thinking it's just the boundary of the volume that is fixed? The volume of fluid inside the control volume can change, over time?
0
votes
0answers
30 views

The velocity of air on an airfoil

They say that velocity of the top layer on an airfoil is higher than the lower layer. But, according to the continuity principle of fluid, the velocity of air is inversely proportional to the surface ...
2
votes
2answers
172 views

Backwards airflow in a Venturi tube

When air is flowing through a Venturi tube, it's speed increases at the narrow section. If the airflow is arranged by moving the Venturi tube through calm air, this means air will momentarily flow ...
1
vote
1answer
44 views

Does air speed vary in a jet engine axial flow compressor?

Does it get slower and slower after each stage because of the pressure increase? Or does the shrinking of the space after each stage compensate for this and the air speed at the last stage of the ...
0
votes
1answer
47 views

Using the continuity equation against gravity

Studying Fluid Mechanics right now and in my textbook there is an example of getting water up to a bathroom in a house. We're given the diameter of the inlet pipe and bathroom pipe, but only the ...