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

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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 ...
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40 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 ...
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19 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 ...
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21 views

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

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.
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35 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. ...
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94 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 ...
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15 views

water pressure relationship to volume [on hold]

I have a one inch pipe 120 feet long and caped. I have a 60 pound input of pressure. I put a half inch pipe at the end and open it. What happens to the pressure in the one inch pipe? If I add another ...
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38 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 ...
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frequencies that affect newtonian and non newtonian liquids [on hold]

I have a science fair coming up and i need to know which sound frequences affect liquids, both newtonian and non newtownian. i also need to know the science and formulae behind it. Your answers will ...
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19 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 ...
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21 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 ...
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39 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 ...
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69 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 ...
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39 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)?
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1answer
39 views

Velocity field of solid body rotation [closed]

Consider a fluid in solid body roation about the z-axis with angular speed $\varOmega$ Derive an expression for the velocity field (u(x,y), v(x,y)) and show the vorticity of this velocity ...
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47 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?
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28 views

Wind blows to surface, how long legs I need? [closed]

Wind blows onto the surface normally at at speed of 20m/s. The frame (in vertical plane) has two supporting bars in the plane of the ground as shown welded rigidly. What is the length of horizontal ...
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16 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 ...
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13 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 ...
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36 views

How can I add a rounded trailing edge to an airfoil? [closed]

I have an airfoil coordinates file (NACA 65(4)-421) with a sharp TE. I need it to be rounded. It doesn't seem that there are any tools available to help with this, so I've tried making my own Python ...
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2answers
78 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
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15 views

Find parameters of blood constitutive equation [closed]

I used a viscosimeter to study the rheology of blood. I have data of viscosity, speed, shear stress and shear rate. I want to find the parameters of the constitutive equation of blood: , where ...
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2answers
30 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 ...
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107 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 ...
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365 views

Why does the lake surface appear darker in some areas?

My question: What causes the surface of the lake to appear darker in some places? My take on the matter: Firstly, I don't dare to say it's fishe which cause it. Secondly, the dark surfaces move ...
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28 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 ...
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225 views
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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 ...
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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 ...
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22 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 ...
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42 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 ...
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23 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 ...
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53 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?
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1answer
19 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 ...
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1answer
19 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 ...
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130 views

Why pouring milk from a height makes a chain shape?

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 ...
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1answer
39 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 ...
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1answer
28 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 ...
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26 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 $E$ ...
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20 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 ...
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33 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 ...
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1answer
64 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?)
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34 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 ...
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2answers
48 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 ...
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2answers
43 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 ...
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24 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?
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1answer
24 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?
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26 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 ...
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2answers
86 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 ...
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1answer
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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 ...
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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 ...