The motion of fluids (gases, liquids and granular material).

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What about negative Pressure?

Here is something I see : Let's say the ideal fluid(water here) of density $\rho$ is drawn from a source by a motor and thrown upwards with a velocity $v$. Now we take the power of motor be ...
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4answers
560 views

Zigzag flow of water along a vertical glass window

I've observed this behavior many times. When it rains, the rainwater will form vertical channels along a glass window. The flow of water is mostly confined within these vertical channels and the ...
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2k views

Why does water gulp out of a water bottle with a narrow opening instead of a steady flow?

For example, take a water bottle. Fill it with water and then turn it upside down. Instead of flowing steadily downward, it gulps down in parts. Why?
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30 views

Intuitive explanation of Poiseuille's law — why $r^4$?

According to Poiseuille's law, the effective resistance of a tube is inversely proportional to the fourth power of its radius (as given by the following equation). $$R = \frac{ 8 \eta \Delta x}{\pi ...
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1answer
277 views

Why do air bubbles stick to the side of plastic tubing?

I'm watching water with air bubbles flow through transparent plastic tubing. The inner diameter is a few mm. Bubbles typically are the same diameter as the tubing, with length about the same or up ...
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884 views

When is a flow vortex free?

To solve problems in fluid dynamics one states often the assumption that the flow is vortex free i.e. $rot(u) = 0$ It is a basic assumption which is needed for potential flow problems etc.. My ...
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How is possible for current to flow so fast when charge flows so slow?

How is possible for current to flow so fast when charge flows so slow? We know electrons travel very slowly while charge travels at ~the speed of light.
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Flow of liquid among branches

If water is flowing through big pipe is branched into 4 branches of small pipe. Lets say the flow is around 4 m/sec. I have the following questions: What will be the flow rate in each of the ...
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1answer
147 views

Velocity of a viscous fluid through a tube

When a viscous liquid flows through a tube in a laminar flow, why is its velocity highest at the center? I understand the concept of shear viscosity and why the liquid in contact with moving plate ...
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1answer
710 views

What's the shear rate in a turbulent flow?

The explanation of shear rate in laminar flow is straightforward: We imagine small layers of fluid that glide on each other. Now, in turbulent flow, this does not work as there are no layers. I'm not ...
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736 views

Physics behind the flow of gas coming out of a balloon

I'm working with stratospheric balloons (latex ones) and I want to put a valve on it so it can float for a longer time. I'm trying to define which valve I should use, which demands I estimate the flow ...
4
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1answer
860 views

Air flow coming out of a fan feels much stronger than air flow coming in. Why? [duplicate]

Possible Duplicate: Why is exhaling more forceful than inhaling? If I put my hand behind my computer's system block, I can feel a very strong flux of air coming out, as it is being pushed ...
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1answer
326 views

Compressible fluid flow through a branched pipe junctions

Backdrop: Designing a dust extraction system (LEV) with a branched junction. What principles allow for the calculation of volume flow rate and pressure at the inlets if the volume flow rate and ...
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5answers
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Will adding heat to a material increase or decrease entropy?

Does adding heat to a material, thereby increasing electrical resistance in the material increase or decrease entropy? Follow up questions: Is there a situation were Heat flux ie. thermal flux, ...
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2answers
641 views

Vortex street and Reynolds number

Its been stated in Wikipedia regarding Reynolds number(Re) that "laminar flow occurs when Re<2300 and turbulent flow occurs when Re>4000. In another wiki file related to Kármán vortex street it has ...
3
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1answer
66 views

Mathematically impossible for a vortex line to have loose ends?

Could someone show the math behind it? Source : "A vortex is a bunch of air circulating around itself. The axis around which the air is rotating is called a vortex line. It is mathematically ...
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1answer
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how to determine if a vortex is laminar or turbulent

In a cylindrical chamber with a high diameter-to-height ratio; a fluid is tangentially injected. there is an axial exit to the cylinder. how do I determine if the vortex so formed is laminar or ...
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3answers
192 views

Analogies between physics and packet-switched networks

Suppose two entities in a communication networks (sender and receiver) are connected with a tube so that water can be pumped from the sender to the receiver. If we also assume that between sender and ...
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1answer
832 views

Static flow of water in the presence of a loudspeaker

The title, I don't know whether it's correct or not, but I came across a video in youtube, http://www.youtube.com/watch?v=_PkgQQqpH2M. The author of video used the title and hence I used the same. ...
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1answer
118 views

What is the math/physics behind maximizing tinker's damage?

Tinker is a hero in the popular game Dota 2. He has a spell called 'March of the Machines' that creates a stampede of little robots in a rectangular area. The robots do damage on impact of an enemy ...
3
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1answer
53 views

Torque on a rotational cylinder in viscous fluid

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 ...
3
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0answers
138 views

SU(2) critical point and volume dependence

I am doing multi-dimensional plots of $\beta_j$ for SU(2) for infinite volume to understand the flow behavior and I was wondering, before I go too much further, if anyone knew off the top of their ...
3
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2answers
67 views

What makes laminar cascade break?

Near my house there is a mall that have a cascade, which has a pratically constant flow, and doesn't seem to have perturbations (at least near the edge where water falls), between its two levels. ...
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3answers
1k views

What is the velocity area method for estimating the flow of water?

Can anyone explain to me what the Velocity Area method for measuring river or water flow is? My guess is that the product of the cross sectional area and the velocity of water flowing in a pipe is ...
2
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1answer
78 views

Whirlwind/tornado/dust devil in the middle of nowhere

I live in area which have many properties similar to desert. Many times when I drive by I see a whirlwind/tornado/dust devil of sand or other garbage parts. I would like to ask how this was normally ...
2
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2answers
172 views

The criteria for potential flow theory

I am learning aerodynamics. In this course a potential flow is denoted that a flow in which the rotation is zero everywhere. But the book told me that we can add vortex into a flow field, and we can ...
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1answer
941 views

What is the shear stress of a fluid?

One book defines the shear stress $\tau$ of a (Newtonian) fluid as $$\tau = \eta \frac{\partial v}{\partial r} $$ where $\eta$ is the viscosity. There is not much context, so I've made some guesses. ...
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1answer
61 views

Continuity and Blood Flow

Consider a tube with two different diameters (one section wider than the other). Because what comes in must go out (conservation of mass), the flow rate in the wider section must be the same as the ...
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2answers
4k views

Does pressure drop across pipe affect flow rate?

Let's say there is a main pipe containing $100\: \mathrm{m^3/hr}$ a fluid of density $750\: \mathrm{kg/m^3}$ and it's gonna be branched into 2 pipes (Pipe A and Pipe B) of the same diameter. If Pipe A ...
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3answers
432 views

Steady isothermal flow of an ideal gas

So I have a steady isothermal flow of an ideal gas through a smooth duct (no frictional losses) and need to compute the mass flow rate (per unit area) as a function of pressures at any two different ...
2
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1answer
58 views

Is there a name for a quantity that represents (volumetric) flow per unit of mass?

In a lot of medical literature about blood flow in the brain, researchers denote the amount of volumetric blood flow that passes through a certain amount of brain tissue as "cerebral blood flow". ...
2
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1answer
210 views

Experimental measurement of volumetric flow rate

The other day I with my team had to measure the volumetric flow rate through a pipe only using a 2000 mm$^3$ volumetric flask and a chronometer. The end of the pipe discharged to the atmosphere. As we ...
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3answers
416 views

Is there other uses of flow-straighteners than flow-metering?

Flow-straighteners are used before flow-meters because they remove disturbances from the flow and achieve nearly-fully developped velocity profiles. But is there any other uses of flow straighteners ...
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1answer
63 views

Why does (potential) fluid flow bend around a solid surface in the flow?

Potential flow obeys Laplace's equation with certain boundary conditions (i.e. no fluid penetrates the solid body in flow, and far away from the body, the flow is uniform with a given velocity and ...
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1answer
76 views

Non-determinitric flow of water stream on vertical porcelain surface

I noticed several times while washing my hands that accumulated water when starts streaming vertically does not flow vertically in straight line on vertical porcelain surface under the force of ...
2
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1answer
145 views

Application of plasma actuators for flow control of moving objects

I've recently been to a converence on plasma physics were, to my surprise, a lot of presentations were concerned with plasma actuator. Could someone, preferably in the field, tell me how long people ...
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3answers
803 views

Riddle: can you swim faster upstream than downstream (with respect to the water)?

A friend of mine posed a riddle to me: A man swims upstream in a river, which is flowing at an unknown rate. He is wearing swimming goggles. At a certain point he loses his goggles. 10 minutes later ...
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1answer
341 views

Calculating spacecraft water leak flow rate

A large container of heated water is floating in space. How can I calculate leak rate if a small puncture is opened? I'm assuming the water is kept at 298K and in the liquid state inside the chamber. ...
2
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1answer
67 views

Laminar flow in low-permeability material. Which is faster, gas or a liquid?

I consider a simple low-permeability material $(k \sim 10^{-18}\;\text{m}^2)$. Now I either apply a gas (e.g. nitrogen) pressure or liquid (water) pressure of - let's say $10\;\text{MPa}$ - on one ...
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Modeling Syringes e.g. with the ideal gas law

Gentlemen I have a similar yet very practical problem that might provide further insight. I'm trying to model a moving plunger in a syringe (something like a piston in a cylinder). At time zero the ...
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60 views

Contraction and expansion after constricting flow though a pipe

If an orifice is placed inside a pipe with a smaller diameter than the rest of the pipe, fluid will follow a curved path in order to enter the orifice, and then expand. I was wondering at what ...
2
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1answer
847 views

How much water must flow trough canal to maintain a constant water deep?

In order to maintain a constant water deep in canal, how much water must flow trought the pipe ? As shown on picture, canal have a rectangular shape. I don't know if canal length have an influence. ...
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30k views

Relation between water flow and pressure

Is there any equation that states the relation between pressure and water flow. I.e. Let's say that in 1 hour with 8mca (water collum meters) pressure I obtain 50m3. What if (giving the same ...
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1answer
325 views

Hamiltonian Flow Map

I'm reading this article and am struggling with some of the terminology. What is the flow map for a Hamiltonian system? I'm looking for a rigorous definition really! Many thanks in advance.
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1answer
107 views

Computational Fluid Dynamics methods

I have read some articles about the finite difference method on a cartesian orthogonal grid. I understand how it works when Dirichlet boundary conditions are used, or when Neumann boundary conditions ...
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1answer
92 views

Bernoulli's principle

In steady flow, the air that flows faster causes a lower pressure, the lower pressure causes it to move faster, or exactly both at the same time? Also how is it that we're talking about the pressure ...
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3answers
108 views

Does the equation of continuity hold for turbulent flows?

My textbook mainly deals with laminar flows. The book derives the equation of continuity, which states that the cross-sectional area times the velocity of a flow is always constant. But nowhere in the ...
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2answers
244 views

Water draining from a height into the bottom of a reservoir

If I hang one 5 gal. Bucket directly above another, put a hole in the bottom of the upper bucket with a tube inserted just inside hanging all the way to the bottom of the lower bucket and fill the ...
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1answer
154 views

What is the term for heat generation by a flowing fluid?

I would like to know more about the heat distribution over time in a flowing liquid. To this end, I consider the Navier-Stokes equation (where the coefficients may be temperature dependent) and the ...
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2answers
31 views

principle in a water Faucet [duplicate]

If you try to block with your finger the flow of the water out of the faucet or a water hose, the water's speed increases. But while you're blocking the water flow out of the faucet by turning the ...