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

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Velocity of water column

If an air filled tube 5 km long with a diameter of 20 m was submerged vertically under water one end 5 km underwater and the other end at the surface, how fast would the water column rise if the ends ...
6
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1answer
201 views

Why do flat sheets of paper twist more than paper cones as they fall?

If I cut a 10cm circle out of a piece of paper and drop it, it will twist as it falls, even if it's rigid. If I then cut out a one-quarter wedge of the circle and tape the remaining three-quarters ...
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1answer
114 views

Velocity of water from tap to fill a cracked bucket to brim

Let us consider a real life situation. The bucket in figure below (drawn using MS PAINT) has an irregular crack of essentially small area. And I decide to open a tap above it and start filling it ...
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3answers
37 views

Modelling an Airplane Question

For an assignment of mine I am creating a very basic model of an airplane, where I choose to consider a fixed amount of parameters that affect flight and to disregard others which I find too difficult ...
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1answer
783 views

Conventional definition of ideal fluid

According to Landau&Lifshitz, an ideal fluid is one with zero viscosity and a negligible thermal conductivity. This is also the FR.wikipedia version: En mécanique des fluides, un fluide est ...
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1answer
66 views

Derivation of the relativistic equation of energy conservation for a perfect fluid

I'm currently attempting to struggle through the first chapter of Sean M. Carrol's spacetime and geometry. I'm a bit stuck, most likely because of not understanding the mathematical operation. ...
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107 views

What is the exact value of the constant in the similarity solution for blast waves?

Recently I used the Rankine-Hugoniot equation to reason that the limit of the speed of shock waves for extremely strong shocks is $\bigl(\frac{6P}{5r_0}\bigr)^{1/2}$ where $P$ is the pressure of the ...
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1answer
35 views

Noncoalescingِ drops on vibrating liquid surface [duplicate]

if you set a dish filled with soapy water onto a loudspeaker or other vibrator and make vibration, When it oscillates, it is possible to hold small droplets on its surface for a long time. I mean, ...
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1answer
50 views

Ball touching the side of a tube — DOUBT

I have a small doubt in understanding a physics concept. If a steel ball is dropped in a thin tube of glycerol, it will eventually reach its maximum or terminal velocity. However, if the steel ball ...
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2answers
225 views

Torricelli's speed of efflux law

Torricelli's law states that if we make a hole in a container of fluid open to atmosphere, then the speed of the fluid spouting out is: $$\sqrt{2gh}$$ Does this velocity correspond to the horizontal ...
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1answer
26 views

What is the short time limit of Maxwell viscoelastic fluids?

The Maxwell model for viscoelastic fluids writes: $$ \tau\stackrel{\triangledown}{\sigma}+\sigma=2\eta D(v) $$ where $D(v) = \frac{1}{2}(\nabla v +\nabla v^T)$, $v$ velocity and $\sigma$ stress tensor ...
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0answers
41 views

Flow Rate in a tube with zero roughness [closed]

Assume the following setup. Given the Diameter of the pipe, difference in elevation (z1 - z2), pipe length, what would be the theoretical way of determining the flow rate (Q) within tube? Assume ...
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22 views

Noise created due to change in Air Pressure

Background : My blower in one of the experiments is generating noise due the a short airflow path to atmosphere. The reason is due to a sudden change in pressure (high to low) the high noise is ...
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1answer
443 views

What's the efficency of a steam jet pump?

Jet pumps or venturi pumps are often stated as having a "terribly low" efficiency, steam jet pumps specifically are usually describes as "only justifiable when there's an abundant steam supply anyway" ...
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0answers
73 views

How to calculate velocity of air through a pipe? [closed]

I was wondering if there is any equation that helps to calculate air velocity through a pipe? I cannot find anything although I did find that velocity of air (not in a pipe) can be found by: Is there ...
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1answer
51 views

Noncoalescing and bouncing droplets

if you set a dish filled with water onto a loudspeaker or other vibrator and make vibration, When it oscillates, it is possible to hold small droplets on its surface for a long time. I mean, when you ...
0
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1answer
23 views

Can cyclic acceleration/deceleration be worse for fuel consumption?

Recently I have started to drive my car slower on the highway in order to save money on gas. However, I feel like I am spending at least as much fuel as before. One possible explanation that I thought ...
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2answers
307 views

Does continuity equation hold if the flow is accerelated?

I'm Studying the streamline flow, specifically the continuity equation Bernoulli's Principle. Consider the following system where a liquid flows through the pipe of a uniform area of cross section ...
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0answers
23 views

Bernoulli principle and viscous loss

Imagine I have a fluid flowing at a rate Q in a closed circuit with no viscous losses (Bernoulli's principle applies + total energy is equal to the kinetic energy). Now, I add a resistor with ...
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5answers
3k views

When pressure is exerted on parallel hydraulic pistons, do they start extending at the same time?

If there are two hydraulic cylinders connected in parallel, each with a different load (shown in the picture below), will they start extending at the same time? I'm having a disagreement with my ...
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0answers
60 views

In enthalpy, is PV the pressure energy?

In the case of a fluid, does the $PV$ contribution to the enthalpy correspond to the pressure energy in fluid mechanics? (Related: What is Pressure Energy?)
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3answers
476 views

Why do rain waves form and what is their connection to the texture of the surface they're on?

When it rains and water flows down an inclined street, ripples may form that are carried along with the current. Here's a picture with an example of what I'm talking about I'd like to know what the ...
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1answer
33 views

Why do we need the kinematic viscosity?

Kinematic viscosity is the well known dynamic viscosity divided by density. What difference does it make to divide by density? What is so useful about this?
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4answers
1k views

Is the velocity with which molecules of the medium oscillate same as velocity of the sound in that medium?

I wanted to know that under sound field applied molecules of the medium oscillate with some velocity in the direction of sound propagation. Is this velocity same as velocity of the sound in that ...
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2answers
94 views

What do the differences between spatial and temporal spectra imply about the structure of turbulence?

In the study of turbulence (theoretically, computationally and experimentally), we often appeal to Taylor's Hypothesis, which (very loosely) summarized means taking measurements at one point in space ...
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3answers
667 views

Occurrence of turbulence in fluid dynamics from the equations of motion?

How can it be shown that turbulence occurs in fluid dynamics? I think people imply that it develops because of the $\text{rot}$ terms in the equations of motion, i.e. the Navier-Stokes equations, ...
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20 views

Heat system: Dynamic - quasi-stationary - static

I am an engineer in the field of district heating and in the future I will work together with people from computer science and physics. I have a question regarding dynamic/quasi-stationary and ...
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2answers
608 views

Energy from man-made tornadoes

Peter Thiel just paid $300,000 to Canadian inventor Louis Michaud who is working to construct useful "man-made tornadoes" or "atmospheric vortex engines" which could be components of future power ...
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1answer
36 views

Symmetry Arguments: Flow Through Cylinder

Why can for symmetry reasons a steady, viscous, incompressible flow, obaying the N.S equation: $$\rho(v \nabla)v = -\nabla p + \eta \Delta v $$ That flows through a cylindrical(very long) pipe not ...
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1answer
131 views

Current density in phase space

$\newcommand{\dd}{{\rm d}}$ I have a question which arises from looking at the impact free Boltzmann equation. Let $(\vec{x},\vec{v})$ be a vector in our phase space $\Gamma^N = \mathbb{R}^{6N}$. The ...
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0answers
45 views

Toricelli's law of efflux in moving container

Suppose there is a big tank of water with a small hole near the bottom. Now if this tank starts moving with say a velocity 'v', then will Toricelli's law hold? I tried directly applying Bernoulli's ...
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3answers
993 views

Is Torricelli's law “wrong” for big holes? - Tank draining problem

Consider a tank full of water with a constant cross-sectional area A1 placed vertically on the ground. Now someone drills a hole of an area A2 in the bottom of the tank, and the liquid starts escaping ...
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2answers
82 views

Pressure in a fluid

If a fluid is flowing along a vertical line with a constant velocity, will the pressure at every point be the same and irrespective of height?
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1answer
42 views

How should I think of a liquid in terms of interatomic potential and molecular speed?

A rather simple question for liquids specialists I guess but I have hard time finding information about this. Here is my problem. I understand the ideal gas theory and the Maxwell's speed ...
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1answer
44 views

Question about propellers

A ship moves forwards because a rotating propeller sends water backwards. The diameter of the propeller is as large as possible because in order to be efficient it must push the the greatest feasible ...
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1answer
29 views

How are probe liquids selected for Surface Energy measurements?

Why are water, ethylene glycol and diiodomethane generally used for surface energy measurement?
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1answer
47 views

Conterflow heat exchanger with different flow rates

If we have tube in tube heat exchanger, in classic situation surface area in contact with both fluids is the same (if we ignore wall thickness of the tube). If fluids have significantly different ...
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4answers
60 views

What makes the magnitude of the force of friction velocity dependent in one scenario, but not the other?

When a solid objects makes contact with another solid object, I believe the magnitude of the force of friction between them does not depend on the relative speed of the two objects. When a solid and a ...
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2answers
597 views

Why does this capillary action generator not work?

So I was doing a bit of reading. Apparently the the obstacle to generating energy from the forces driving capillary action is breaking the surface tension at the top of a capillary tube. It is just ...
3
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1answer
2k views

Torque on a rotational cylinder in viscous fluid [closed]

I've been stuck on what I'm pretty sure is a simple part of a larger question. It's a cylinder (radius a) spinning in a viscous fluid. It's rotating at rate $\Omega$ .During this question we get that ...
7
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1answer
275 views

Why Are Normal Shock Waves Unstable in a Converging Channel?

While learning about shock waves in an introductory Gas Dynamics course, it was revealed that normal shocks are unstable if formed in a converging channel. Even if the local conditions ostensibly ...
3
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1answer
785 views

Perfect fluids in cosmology?

In cosmology, it is often assumed that the equation of state of a cosmological fluid is of the form $p=w\rho$. Why is this? Is it the equation of a perfect fluid? Why does $w=0$ for matter $1/3$ for ...
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0answers
26 views

How can frequency of waving in water change the direction object on the surface goes?

In an Australian experiment the physicists studied effects of a simple object that causes waves in fluid. They found that if it vibrates slow, the objects on the surface moves away from the vibration ...
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25 views

Equation of state for a radiation fluid

Can anyone give me (point me to a reference of) a derivation of the equation of state for a radiation fluid: pressure = energy/3 Much thanks.
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1answer
52 views

Terminal Velocity in Water

Another question concerning classical physics. On Earth, the combination of air resistance and gravity interact in a way that creates the phenomenon of terminal velocity. Do other fluids (for example, ...
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0answers
35 views

What makes some air bubbles in water more persistent?

In a plastic bottle of water, near the walls, it is common to observe the presence of little bubbles (I would estimate them to be $\approx0.5$mm in diameter. In my experience, most of these bubble ...
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1answer
108 views

Using water pressure as pushing force in a floating bath tub? [closed]

Does physics allow for water pressure to work in this way? if so What formula can prove this? (backup link 1, backup link 2)
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2answers
46 views

Why do bubbles group when one pops? [duplicate]

I was recently observing the way bubbles move as they pop and disappear. I noticed that when bubbles destabilize and pop, the remaining bubbles immediately surrounding it will move to fill its place. ...
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1answer
119 views

Rain system movements and highways?

In my free time I sometimes enjoy watching the weather or radar and trying to predict how a rain system will move. Pretty often I notice that a small rain system or even a large one will congregate or ...
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34 views

Gas diffusion through a flat plate boundary layer

Set-up Suppose we have a flat plate with a flow of gas parallel to the plate. The flow creates a boundary layer on the surface of the plate. Now, the gas is carrying a reactive species, which is ...