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

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Force of Leaky Bucket over time

Indie Lab Procedure: I attached a cylindrical can to a force sensor. On the bottom of the can I drilled holes of various diameters. I then added a volume of water while collecting data from the force ...
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10 views

Reactor opening and total time to reach a specific temperature

Let's say I have a reactor (we assume that its shape can be approximated by a horizontal cylinder) in which there is air at the temperature of 1000K and at pressure of 1.5 bar. Now, I want to open it ...
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37 views

Fluid Dynamics - How does air behave out a window?

I often smoke out a window, and I know that if you're driving a car, the passing air will affect the pressure inside and "suck" out the smoke for instance. But what if you're in a window pane? I have ...
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44 views

Self similarity for slowpokes

I am struggling with the concept of self similarity. If I google search, I either find examples that don't explain all too much or detailed explanations that go waaaaay over my head. I've found a ...
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1answer
46 views

Friction in a fluid

when an object is moving in a fluid(air for example), the air will resist the object's movement: molecules of the air will collide with the surface of the object (no slip condition) and then we will ...
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295 views

Calculating flow rate of a syringe

I wanted to know how would I go about calculating the flow rate of a syringe with a metal tip that is dispensing water using a pressurized air. I have had a look on internet about this and on this ...
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178 views

Finding diffeomorphism given vector fields [closed]

Given a vector field how do you find the associated diffeomorphisms? Say I am given a vector field in Minkowski space $$\xi = x \frac{\partial}{\partial t} + t \frac{\partial}{\partial x}.$$ How do ...
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73 views

flow rate in split bottleneck

water flows from top to bottom. first there are two pipes, one with 10 LPM max flow rate and another with 20 LPM max flow rate. they both go to another pipe, which is 20 LPM max flow rate. the total ...
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80 views

How viscosity and velocity relate in a pipe?

Assume we have a pipe that there is a fluid stream in it. By increasing the velocity of the fluid the resistance will increase either (because of the viscosity I think). My question is how are these ...
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38 views

Can a compressible fluid flowing , change its speed in the absence of a pressure gradient?

I've heard that in a high velocity nozzle, any random 'fluid particle' experiences an increase in kinetic energy at the cost of internal energy and pressure energy.And I do understand that for any ...
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91 views

If I was to poke two holes in a water filled balloon would it lose water twice as fast a a balloon with one hole?

if I was to assume that the only force behind water coming out of the holes is the pressure i.e., the height of the water remaining which is constantly changing (declining) as water leaves the ...
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61 views

Streamlines and ideal / real fluids

I was going through some basic description of streamlines in which I noticed that streamlines in an Ideal fluid where shown "equidistant" from each other at a place . whereas in the real fluid ...
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116 views

Streamlines and line of flow of fluid particles

I am very confused with this thing can someone clarify these problems given below-- 1 //Do or can the streamlines of a fluid particle show the position of the particle at a time( using the ...
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58 views

Drag Force on a cylinder with its long axis aligned with the flow

yesterday I started looking into equations that link a cylinders diameter $r$ and length $L$ to the force experienced in a highly viscous medium ($Re<<1$). I found the onseen-approximation but ...
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2answers
304 views

Does water follow the path of least resistance

I am having hard time proving this either right or wrong. Let's take for example a river, does the water flowing down follow the least resistant path?
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42 views

Angular momentum transfer in a bottle vortex

A colleague and I were discussing the following fluid mechanics experiment, which most people have probably tried in their kitchen: take a bottle full of water (a 2-litre transparent soda pop bottle ...
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307 views

Piezoelectric water flow detection

Can a piezoelectric sensor detect constant water flow, or just the moment when the water is turned on and off?
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30 views

What is the difference between hydraulic radius and geometrical radius in a cylindrical pore?

What is the difference between hydraulic radius and geometrical radius in a cylindrical pore? I was going through the 'stacks' present in an thermoacoustic refrigerators there I came across the ...
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1answer
179 views

Is there a theoretical limit to the maximum flow through a pipe?

Assuming laminar flow, the Hagen–Poiseuille equation defines the flow rate as a function of the head pressure. However as the flow rate increases so does the head loss due to friction within a pipe, ...
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49 views

What laws of physics apply when a flow of air is divided?

The question is rather simple, but I'm not sure if there is a simple answer to it. Let`s say I've got a flow of air (5 bar, 25 l/min) running through a 6mm hose. Then this flow hits a branch dividing ...
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278 views

Turbulent and smooth flow of water from a tap

When water flows normally from a tap, we can say it is turbulent ( Pic 1 ). But when we attach a piece of cloth to the opening of tap, water flow becomes smooth ( Pic 2 ). We can say that by touching ...
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70 views

How do cyclonic dust separators work? [closed]

I have a background in engineering so I am somewhat embarrassed to say that I don't understand how a seemingly simple cyclonic dust separator works. Here is a link to video of such a device in ...
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1answer
73 views

Perturbations on a fluid thread and hydrodynamic instability

I know that due to fluid instability there are some perturbations ( picture below ) after all of these, my question is the reason of existence of these perturbations. Why exactly they appear? Shear ...
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1answer
75 views

growth rate of the instability of a laminar flow?

I was just studying something about The Plateau-Rayleigh Instability that I saw something called Growth rate of the instability. My question is the exact physical definition of growth rate of ...
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1answer
49 views

Is there an equivalent of probability current for the Wigner distribution?

I know that for a wavefunction, I can derive a probability current $\mathbf{J}$ that satisfies the continuity equation: $$\nabla \cdot \mathbf{J}=-\frac{\partial}{\partial t} \big|\psi\big|^2$$ Can a ...
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1answer
100 views

Why in fluid interface, liquids tend to reduce their surface?

I've read something about fluid interface and know that liquids tend to reduce their surface but my question is that why do they tend to reduce their surface?
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1answer
114 views

Stationary waves on a laminar liquid flow near collision with a surface [duplicate]

Look at the picture below I know about plateau rayleigh instability. And my opinion is that the reason of this phenomena is plateau rayleigh instability. But there's a question, in the picture ...
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33 views

How to calculate the depth of a flow meter so that there are no air bubbles in the stream

A mix of air and water (foam) is flowing into a tank from the left and going out to the right. To the right there is a suction pump. The tank is divided by a middle vertical wall that stretches from ...
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129 views

What is the difference between flow and expansion?

Fluids (both liquids and gases) will move from one point in space to another due to a potential gradient. Some examples may be: 1) horizontal pipe flow, a fluid will move from a region of high ...
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88 views

How do I convert pressure and flow from Imperial to metric units?

I'm not a physicist or have much experience in engineering. However, for a programming task, I need to change code that calculates "pressure, head, feet of fluid, gauge" into "meters of head, ...
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83 views

volumetric flow rate due to Bernoulli's principle

for calculating the volumetric flow rate of a liquid coming out of a tube, I know that If the pipe is too short, the Hagen–Poiseuille equation may result in unphysically high flow rates; the flow is ...
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63 views

Why is temperature a function of $y$ and $t$ only?

Say you have an incompressible thermal conducting fluid contained between two infinite horizontal plates separated by a distance $H$. Initially both the plates and the fluid are at rest at ...
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1answer
101 views

Find the separation distance for a line of oil being squashed between two flat plates [closed]

I was wondering if someone could give me some help on how to start this problem, I'm really struggling to get my head around it. A long line of oil is being squashed between two flat plates of length ...
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77 views

How to make two equations dimensionless? [closed]

I recently got set this problem and am having trouble scaling the resulting equations. Any help would be appreciated. An incompressible thermal conducting fluid is contained between two infinite ...
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62 views

Open systems (Conservation of Energy): is a temperature change possible if a tube is thermally isolated?

Full question: consider an perfectly thermally isolated cylinder. Water is flowing through this cylinder from the entry to the exit. Is it possible for the water flowing through the exit to have a ...
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450 views

The pressure in a container of water is based on depth. So what happens if I remove the bottom of the container?

So I understand that if we have a system that involves a container of water the pressure will equal atmospheric pressure at the top and as we go further down the container the pressure will increase ...
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38 views

How can I interpret $P(t) = \frac{1}{Q(t)} \frac{dW(t)}{dt}$ physically?

Generally speaking, one can calculate the work, $W$ (energy) required to compress a volume, $V$ of gas by integrating the pressure-volume 'loop' in a phase-space as $$W=\oint PdV$$ where $P$ is the ...
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78 views

On deriving a fluid flow pressure drop model using either physical theory or empirical methods

I'm trying to derive a model from physical principles of fluid flow, a simple quadratic model that tends to well fit actual pressure-flow data. For (real) subsonic air flow (ideally adiabatic) ...
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68 views

Pressure profile and output of a coil heated burner

In a hot air balloon burner (and probably lots of other burners) liquid gas is passing through a heating coil before it exits at a hose. I realize that the point of having a heating coil is to ...
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141 views

What is the meaning of the point of inflection in this?

Consider the following flow velocity profiles near a boundary, and the boundary profile point of inflection,PI Regarding the effect of pressure gradient on boundary-layer profiles does the point of ...
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3answers
896 views

Laminar vs Turbulent flow separataion

(Left is a laminar separation, Right is a turbulent separation) I have been having a bit of trouble understanding this concept. How come the laminar separation involves a much larger wake than the ...
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50 views

Constant RPM of Gas Compressor

I would like to improve my understanding of gas compressors. If the compressor is moving at constant RPM, does it mean that it can only allow the same volumetric flow rate at all times? So the power ...
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155 views

Magnus effect, Coanda effect, and the Bernoulli principle: What is balancing gravity on a spinning sphere vs. a stationary screwdriver?

I've seen videos of golf balls and screwdrivers levitated by a focused air stream. Reading the comments of these videos (and others), I see explanations of the machanics at work and their cause and ...
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2answers
507 views

Why does the vortex form in the von Karman Vortex Street?

Why does the vortex form in the von Karman Vortex Street? So far I have this for the reasoning: 'It occurs when a fluid flows around a cylindrical object. The pressure on a fluid particle rises to ...
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2answers
589 views

Calculating the drag force provided by a laminar flow [duplicate]

If I drop a ball into viscous fluid (e.g. oil), by calculation I know that the fluid flow is laminar. So which equation do I need to calculate the drag force provided by fluid? The drag equation, ...
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97 views

Connection between gas flow rate and diameter of tubing

First time poster, long time troller and curious student. I have a bit of a conundrum that I would love some input on... Here's the problem. I have an air flow system is under constant pressure of ...
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115 views

Symmetry considerations in Plane Poiseuille Flow

I'm taking a first course on fluid dynamics, and I have this (sort of) conceptual question that's been nagging me for a moment now. I can completely follow the mathematics behind the derivation of the ...
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3answers
171 views

Why are vehicles not pitted like golf balls?

I have read that non-laminar flow reduces drag on blunt bodies. Given that, why is pitting not used on motor vehicles?
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98 views

2D aerofoil fluid analysis - find velocity ratio

I just wondered if you could help me out on this fluid mechanics question? I have worked through it myself but am very unsure of my answer (not yet found the pressure difference) the question is ...
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1answer
2k views

Will changing the pipe diameter reduce the pressure head loss?

I have this system installed in my house (fig 1), and I'm having problems with the shower. I want to know whether, if I change the PEX tubes shown in red from 1/2" to 1" as shown in fig 2, I will have ...