# Questions tagged [fluid-dynamics]

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

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### What are some good resources to learn fluid mechanics? [duplicate]

I know that there are a lot of resources out there to be explored and I have gone through several of them. What I want is some resource where fluid mechanics is treated, from a geometric viewpoint, ...
32 views

### Is vorticity in ordinary liquids such as water quantized?

In superfluid helium, vortexes are quantized. A whirlpool of superfluid helium contains an integer number of these individual vortex quantas. But all physics comes from quantum mechanics. So it would ...
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### Interesting Aerofoil Logical Fallacy

I am new to physics in general having just finished AP Mechanics and have limited knowledge of how fluid dynamics work. But just using forces and a simplified understanding of drag if have come to the ...
1k views

### Open or closed windows in a tornado? [closed]

Should one have the windows open or closed when a tornado is nearby? B.S. in Physics but very rusty in this day and age. I have always been taught that one should keep windows cracked open because of ...
47 views

### Are there any substances that exist as plasmas or supercritical fluids at STP?

If not, why If so, please give some examples
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### Why don't disturbances/wind move at the speed of sound in air?

Why don't sound waves move at the same speed as air that has a pressure differential? Imagine you have a box that is filled with air. One half high pressure air, the other half low pressure. They are ...
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### Calculating tension in a pressurized container [closed]

Suppose I have a pressurized spherical container made of 1 mm thick aluminum. The container has pressure P and internal volume V. How would I calculate the tension in the aluminum? The aim of this is ...
1 vote
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### Can siphons improve the efficiency of hydroelectric dams?

Suppose we have built a hydroelectric dam where the water inlet is 100m above the outlet. We can now use the gravitational potential of the water to spin a turbine. However, suppose we install a ...
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### Why will low pressure pulling higher pressure air towards it make "thrust"? [closed]

Low pressure air means a lack of air molecules. Normal pressure air means a normal amount of air molecules. Say you have a stationary (can't move no matter what) cube of say steel, with low pressure ...
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### Why does the pet's water bowl overflow?

So when i give the pet fresh water in a stainless steel bowl that i place on a mat according to the attached picture, from $t=0$ the bowl is at rest, the water normally oscillates in the bowl like a ...
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### Calculate number of air particles going through a hole in high vacuum at molecular flow

I have a vacuum chamber, connected to a vacuum pump with a pipe of diameter 50mm and need to create a high (0.0001mBar) vacuum. I need to calculate the total suction time, and since I was not in the ...
1 vote
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### Why there is a delay before canned fruits float to the top?

This question may appear silly compared to others asked on this site, yet, I can't get my head around it. After pouring boiling water into a canning jar with berries, berries stay at the bottom of the ...
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### Is air resistance truly linear in surface area?

Air resistance is generally said to be linear in the surface area of the moving object. Out of pure curiosity, I am wondering to what degree this is an approximation, i.e., when this assumption begins ...
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### Incompressible flow condition intuition

The derivation of the continuity equation leads to $$\frac{D\rho}{Dt}=-\rho(\vec\nabla\cdot\vec u)$$ as shown in this wiki article. If we assume that the flow is incompressible, it implies that $\rho$ ...
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### Can one make a jet of air bounce without spreading?

Similar to this reaction on this image (left most) how it keeps its mass without spreading: (Video Link) Is there a way to make a jet of air bounce without spreading? (source)
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### Is there a way to achieve a long jet of air?

As can be seen in the image bellow from a fog/smoke generator machine, the smoke spreads as soon as it leaves the nozzle. (source) Is there a way to achieve a longer jet of air with less dissipation ...
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### Is there any phenomenon where opposite reaction (Newton's 3rd Law) is not fulfilled?

I'm wondering if there is any case in nature/physics where it has been observed "where there is an action, there is not necessarily an exact equal and opposite reaction". Or is there some ...
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### Diffusive momentum transport as overlap of acoustic peaks?

In the context of molecular dynamics simulations of soft or hard spheres in the fluid phase (e.g., with Lennard-Jones interactions), it is known that the velocity autocorrelation function (VACF) ...
1 vote
42 views

### Does the isotropy definition of a perfect fluid imply no heat conduction?

Weinberg defines a perfect fluid (Chapter 2, Section 10) as one where each fluid element appears isotropic in a reference frame moving with that element. From the definition of the stress-energy ...
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1 vote
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### Wave interference and fluid dynamics question

I'm curious to find an answer to this question: In the college canteen I would often slide my Styrofoam cup of milky coffee across the melamine table top. (unlike paper or plastic, Styrofoam is a ...
42 views

### Is the pressure at the top of the wings on Mars also lower than the local atmospheric pressure on Mars?

Generally speaking, on Earth, in order to fly, the pressure on the top of aircraft wings is lower than the local atmospheric pressure. So if we fly an airplane on Mars, will the pressure on the top of ...
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1 vote
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### Boat efficiency [closed]

Recently I was watching a boat race for "all electric boats" that use solar power to drive the engine (no sail only electric motor with solar system). in this race all boats have to be less ...
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### What happens with the water in a pipe when I quickly turn the tap

Assume I have a long pipe of diameter $D$ (e.g. 2cm) and length $L$ (e.g. 10m). The pipe is filled with water. There is a tap at the start of the pipe, which regulates its flow rate. I measure the ...
33 views

### Is Steady Flow necessarily Streamlined Flow? or Vice Versa?

Is Steady Flow necessarily Streamlined Flow? What about vice versa? What is the difference between the two? What conditions should be satisfied for a flow to be streamlined?
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1 vote
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### Add pressure gradient to Falkner-Skan (FS) boundary layer (BL) equations and solve numerically for arbitrary $P(x)$

I have read quite a few tutorials / watched several clips on the derivation of the Falkner-Skan boundary layer equations using similarity and then solution using RK solvers such as ...
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1 vote
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### Why the density have anything to do with initiation of subduction?

No matter wherever I read the process of subduction, I always find this one sentence which says "when the two tectonic plates collide the denser plate gets subducted under the lighter plate ...
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### Which is the cause and which one is the effect between the shear stress and velocity gradient in a fluid flow?

Take a Newtonian fluid flow between two parallel plates, one at rest and one at constant velocity, then there will be a linear velocity gradient between those two plates. Is it due to the no-slip ...
1 vote
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### Bubble behaviour during water / vapour coexistence in the most idealised scenario without boundaries

Consider the following statement: during a 1st order phase transition, the temperature of the system stays constant and any extra heat goes into turning a larger portion of the system into the new ...
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### How to calculate the evaporator and condenser pressure in a vapour compression refrigeration cycle?

Imagine a basic vapour compression refrigeration cycle. A compressor which sucks gas from the evaporator and pumps it into the condenser at high pressure. The gas loses heat and becomes liquid in the ...
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### How to find out if Water Droplet will peneatrate Water Umbrella?

Imagine a scenario. we are pouring water from sink on the spoon, because of that some kind of water umbrella is created by water. Like in this video: https://www.jsme-fed.org/experiment-e/2017_6/001....
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### Will the divergent section of the tube generate pressure below atmospheric pressure?

I noticed the Venturi tube, which is said to generate pressure below atmospheric pressure. It has a convergence section and a divergence section, and I believe that the convergence section will ...
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### A pop pop boat heated with a self-contained heat source and run in a superfluid appears to show a preferred frame [closed]

Suppose there is a pop pop boat but the water is replaced by a superfluid and the candle is replaced by a radioactive heat source The pop pop boat should accelerate forwards; Now let’s imaging a ...
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### Avoiding secondary flow in rotating fluid

I am required to create an annular flume for an experiment. The flume is to be filled with water, and a paddle is to be dipped into the water and rotated along the flume at some fixed angular velocity ...
378 views

### Why do most fish wiggle their tails side to side, and not up-down?

Is moving a vertical fin side to side more efficient than moving a horizontal fin up and down in water for fish locomotion? The answer might lie in how fish propel themselves using vortices, but I don'...
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1 vote
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### Where exactly is the friction with the pipe walls and the fluid? [duplicate]

Is the friction between the walls of the pipe and the no slip layer? Or is it between the no slip layer and the rest of the fluid above?
91 views

### Why does my curry "bounce back" after stirring?

I recently cooked a big pot of curry, consisting largely of coconut milk, a bit of chicken stock and some vegetables. You can probably imagine that it was somewhat thick in consistency. The cooking ...
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1 vote
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### In turbulent flow, where is the friction of the pipe exactly? Is it between the laminar layer and the pipe walls or the turbulent layer and laminar?

In turbulent flow as we get closer to the pipe walls we encounter an overlap layer and then a layer of laminar flow. Also at the walls of a pipe, in turbulent flow, the laminar shear stress dominates. ...
74 views

### Given the same cross-sectional area, is fluid velocity constant?

I'm currently studying a introductory section on fluids and was given this principle of continuity: $$A_1 v_1 = A_2 v_2$$ I understand the logic behind it (viz. the conservation of mass and whatnot). ...
41 views

### Calculating aerodynamic forces on a random object

I've set out to designing a game that would let the user design a vehicle/plane and then fly it around and I'm interested in what would be the best way to go about the physics aspect of it. The 3d ...
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### Fluid flow through a pipe system with diffuser [closed]

I'm brand new to this platform, hope I'm right here. I'm calculating big pipe networks (open systems) with fans using the Hardy Cross method. In this method, I have to sum up all the pressure losses. ...
332 views

### Bernoulli principle (classic form) in irrotational viscous flow (a paradox?)

We derive the Euler equation for inviscid flow. Then, for irrotational flow, we use the Euler equation to get Bernoulli equation (classic form) and show it holds in the irrotational region (still ...
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For an angular velocity function derived by Navier-Stokes, $$\omega \left(r,t\right)=\frac{\omega _0R_0^2}{R\left(t\right)^2}exp\left(-\frac{r^2}{R\left(t\right)^2}\right)$$ from which the azimuthal ...