Questions tagged [fluid-dynamics]
The quantitative study of how fluids (gases and liquids) move.
4,188
questions
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1answer
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How do I calculate the pressure $p_0$ on top of the water reservoir?
Can anyone help me with this question, I can't get the right answer :-)
A water reservoir with depth D=200m, which is placed H=500m above on a mountain. A pipe is placed from the bottom of the ...
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23 views
Why do we consider the viscous force to be tangential?
Is it that since it is a friction force, it needs to be tangential as other friction forces like kinetic friction and static friction forces are?
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1answer
28 views
What is the objective and reasoning of no slip condition? [duplicate]
My Professor used to say that there are two aspects to consider when making an assumption: The purpose of making the assumption and the justification as to why it's scientifically valid.
I would like ...
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1answer
22 views
Pressure in Bernoulli principle
In Bernoulli principle we say that as velocity increases the pressure of fluid decreases but it contradicts kinetic theory of gas which says that as velocity increase-pressure increases. And this ...
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12 views
What percentage reduction in water surface area does induced supercavitation begin to limit propeller thrust? [on hold]
Does a surface drive propeller reduce its power running through supercavitating bubbles?
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26 views
Pipe pressure drop question [on hold]
Water at $20^\circ$C is flowing at $0.1$ cm s$^{-1}$ in a $5$ cm diameter pipe. If the pipe has an equivalent length of 10 m what pressure drop would be expected?
Comment on any assumptions made. Is ...
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What is the lowest-energy configuration of a perfect fluid of constant angular momentum under gravity?
What is the lowest-energy stable configuration of a perfect (homogeneous dense incompressible inviscid) non-oscillatory fluid of constant mass and angular momentum under Newtonian self-gravity?
For ...
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28 views
What are the Shallow water equations in differential form and cylindrical coordinates?
I am ignoring bed height or any other extra terms. The version of SWE when written in cartesian is:
$$
\begin{pmatrix}
h \\
hu \\
hv \\
\end{pmatrix}_t +
\begin{pmatrix}
hu \\
hu^2 + \frac{g}{...
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31 views
Why does the wind close doors?
Assume you have two rooms, both with holes in the wall (more commonly known as open windows), which connect each room to the exterior. The two rooms are connected, but the connection can be closed by ...
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1answer
41 views
Why moving train's windows slam shut when another train passes slowly in the same direction?
My question is related to this one but distinct as this case is trains travelling in the same direction.
We're familiar with this scenario. You're sitting in train A and another passes at high speed ...
3
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1answer
35 views
Is there a Coandă effect outside the atmosphere?
For example, when air is blown through a spoon in the atmosphere, the air flow bends toward the spoon. People say it's the Coandă effect. So, outside the atmosphere, when we let air blow through the ...
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15 views
G Force on Saturated Sediment in a Lake - How to Calculate?
Can I calculate a g force on a saturated sediment in a body of water (a lake bed)? I have a hydraulic conductivity of the sediment and a vertical pore water flux. The pore water is moving upwards ...
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2answers
35 views
How to avoid water tension in a hose?
I am doing a project in which I have to flow water between two containers, which are connected at the bottom by a 1/4" hose. Remarkably, the surface water tension is such that water does not flow ...
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0answers
11 views
What is the behaviour of pressure waves in a diverging-converging cylinder?
Suppose that you have a plane pressure wave that is travelling through a gas in a cylinder (this may be a pipe for instance) such as the one showed below.
What is the behaviour in a diverging and ...
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38 views
How do I determine the shape of steam?
When you dip a fork into a plate of hot food right off the stove and pull it out again with a forkful of food, it generates water vapour steam from the temperature difference. I am wondering how the ...
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1answer
38 views
(SOLVED) Calculate the velocity of a gas inputted in pressure difference
I'm trying to make a generally simple calculation but I'm not sure if I'm approaching this correctly. So as I'm making assumptions solving this problem, please comment or correct me wherever I'm wrong ...
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55 views
Actuator disk: how to find the shape of stream-tube? [closed]
I am trying to understand how one can derive the shape of the stream tube created by an actuator disk shown here
To be more precise,can anyone please point out how can I find the area of the stream ...
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0answers
6 views
Lagrangian formalism to create impenetration condition between two different fluids
Assume that we are given two kinds of fluids that are described by their respective Lagrangian field densities $\mathcal{L}, \mathcal{L'}$. In the case when they are not interacting we assume that the ...
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19 views
Why pressures on interface between two liquids are the same
Assume we have a cylindrical container that has a lower part filled with some liquid, say, water, and an upper part filled with another liquid, say, air. Assume that the interface between them is a ...
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1answer
32 views
The definition of control volume regarding fluids
I haven't seen a clear and general definition of control volume. So if you know one, skip the context below and please give me your definition and sincerely, thank you.
Context:
The union of all the ...
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0answers
39 views
How does a sudden acceleration change split gravity waves into a pair of counter-propagating components? (“instantaneous time mirror”)
The Nature article Time reversal and holography with spacetime transformations is cited by IFL Fluid Dynamics' Waves contain lots of information which includes the GIFs below.
While the paper is ...
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0answers
63 views
Is this a mistake in the text? [closed]
In the book "Fluid Dynamics for Physicists" by T.E. Faber, the author claimed the following (see pic below) without much derivation. But when I derived it instead of a 2, I got a $\sqrt2$ instead ...
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Darcy applied to surface and groundwater interaction?
My question is, in which of these two scenarios would the ponded water drain more quickly?
Darcy's law applied to falling head condition appears to indicate that it would be the a) scenario. I'm ...
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19 views
What is the adverse pressure gradient?
What is the adverse pressure gradient?
Is the pressure gradient increasing along the direction of motion of the fluid a adverse pressure gradient? Does it cause the wing to stall?
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0answers
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Fluid rendering technique (C++/3D) [closed]
I'd like to render fluid based on density value. Let's say I have a cube with 8 points (each of thoses points has its proper density value). So, If i want represent the fluid form on this cubic ...
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27 views
Most efficient method of measuring rate of flow
I understand that devices like venturi meters can be used to measure the rate of flow of a fluid in a closed pipe. There are also devices like the flow meters. But, which one gives a more accurate ...
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1answer
48 views
Using heat to lift a liquid – What's a good way of turning heat energy to gravitational potential energy?
Edit: A bit of context... Living in a country with extreme heat and a lot of hills, many farmers need irrigation pump systems (pump up water from a pond up to a reservoir). I have for example seen ...
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26 views
How can you calculate the total time taken for water to completely flow out of a container given the amount of water initially in the container?
I'm doing an experiment on changing the amount of water in the container and seeing how the time is taken changes with it. The container has a little hole at the bottom where the water flows out from. ...
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0answers
23 views
Drag force as a function of shear & normal stresses
I would like to understand the relationship between the drag force of an object in a fluid and the microscopic interactions between the object and the fluid particles.
Specifically, I would like to ...
3
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0answers
47 views
If a hollow sphere connected to a rope and half-filled with water forms a physical pendulum, what does the water surface do?
Suppose I make a pendulum consisting of a long string connected to a hollow sphere, then fill the sphere half way with water and set the pendulum in motion by giving all the water and the sphere some ...
2
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3answers
94 views
Can the flow be irrotational if the viscous forces act on fluid?
I tried to answer the question only using the definitions and the Navier-Stokes equation:
$$\rho \frac{Dv}{Dt} = -\nabla P +\rho g -\mu[\nabla \times(\nabla \times v)] $$
In my opinion if the ...
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1answer
35 views
Flow in parallel vertical pipes
Consider a tank open to atmospheric pressure, with a large cross-section area A1 and height H, that contains an incompressible fluid.
Two vertical pipes with length H and cross-section area A2 are ...
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0answers
25 views
Relationship between pressure, chamber volume, and flow rate? [on hold]
It has been a while since I took any classes involving fluid mechanics, so bear with my phrasing. I am trying to pump water using a peristaltic pump (Masterflex C/L) with tubing that has about a 1 mm ...
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1answer
42 views
Bathtub boat, is it possible to go forward?
I know nothing would happen when it's just floating. But once I somehow pumped the water to flow out from the shower head, would it keep shooting out water automatically and accelerate the boat ...
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1answer
31 views
Are optimal turbine blades also optimal fan blades?
In one case, the air drives the blade, in the other the blade drives the air.
Since each is 'just' the reverse of the other, one might expect that the aerodynamics are the same, with other variables ...
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1answer
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Would I have to add any additional weight at the end of the lever of well pump (B) for it to lift the same amount of water as did well pump (A)?
The question is if I would have to add any additional weight at the end of the lever of well pump (B) for it to lift the same amount of water as did well pump (A)?
My assumption is yes because of ...
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2answers
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Does density vary with time in a steady flow?
Steady flow is defined as the type of flow where density, pressure and velocity don't change with time, as far as my understanding goes. However, in the video below, they say that the density in a ...
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Center of lift in an aircraft
what is center of lift in an aircraft? How is it different from aerodynamic center and center of pressure? Why is COL important?
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2answers
28 views
Could situation where water does not pour out of a bottle change if different liquid is used [duplicate]
I was washing the dishes and came across a situation that was counterintuitive (at least from my perspective). The situation consisted of a bowl of water and a filled bottle of water. When I dip only ...
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1answer
24 views
Why does water freeze radial around an object?
I noticed an interesting fact today while having a popsicle during my lunch break. When I bit the top of, I could see that in the freezer the ice had frozen radial around the stick. Could anybody ...
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49 views
Cosmology and Fluid Dynamics
What will be the relation between the barotropic index (w) of fluid and the velocity (v) of the fluid ??? and please mention some citation or book.
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1answer
32 views
In swimming why does gliding help keep the head out of water
In relaxed non-competitive swimming, it is possible to keep the head out of the water while gliding. This can be breaststroke or backstroke (or doing the Tarzan stroke in waterpolo). What is the ...
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1answer
23 views
Physical meaning of the convection term in the momentum equation of acoustic wave
In deriving the acoustic wave equation, the momentum equation is used.
$$\frac{\partial \mathbf{u}}{\partial t}+
(\mathbf{u}\nabla)\mathbf{u}=-\frac{1}{\rho} \nabla p$$
Intuitively, the convection ...
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0answers
36 views
Analytical solution to damped harmonic oscillator - Fokker-Planck equation
In the paper "Numerical solution of two dimensional Fokker-Planck equations" (available at: https://doi.org/10.1016/S0096-3003(97)10161-8), the authors quote an analytical solution to the damped ...
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1answer
48 views
Deriving the Navier-Stokes Equation in Fluid Dynamics
I am trying to understand the derivation of the following equation which describes the motion of Newtonian viscous fluids:
Equation 1: $\rho \dfrac{D u}{Dt} = \rho g_x - \dfrac{\partial p}{\partial x}...
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2answers
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Momentum density from stress energy tensor in field theory
Question is similar to one in this link 1.
Let us consider very simple Lagrangian that contains only kinetic energy. Its interpretation follows from saying that the field we are varying $\mathbf{u}$ ...
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1answer
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What happens, if a liquid/gas is kept on constant high pressure in a closed container for a long period?
On applying non-increasing constant pressure,
I need to understand the case for liquid and gas.
If container is not inescapable:
Will the liquid/gas heat up?
Will any of their properties change?
...
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1answer
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Find the expression for $η$ (coefficient of viscosity). For the given condition [closed]
A cube is sliding from wedge with a constant velocity and on liquid of $η$ coefficient of viscosity.The perpendicular distance between cube and layer of liquid is $x$ and the Length of cube is $a$. ...
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1answer
42 views
Time taken by bubble to come to surface
Does air bubble take same time to emerge from shallow water and deep water? I think the acceleration due to buoyancy will be the cause.
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3answers
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Why does surface area not matter when calculating pressure
I can not understand why the surface area that atmospheric pressure is acting upon does not matter when calculating pressure.
For example look at the water jug below with 2 openings, one small and ...
