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Questions tagged [flow]

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

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Convergent Flow [on hold]

Need some help with this fluid dynamics question please. A high-speed drill required cooling to ensure that it does not overheat while in use. To achieve this, high-pressure air is directed through ...
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Problem about fluid flow in a pipe [on hold]

Water at 15°C flows by gravity from one deposit to another, which has its water level 20 meters lower than the first one, on a smooth pipe with a 50 mm diameter and a 100 meters length. Calculate the ...
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4answers
65 views

Calculating value of $g$ from Torricelli's law

For my Physics project, I decided to do an experiment with fluids. I'm using the Torricelli's law to verify that the value of acceleration due to gravity on earth is $9.81m/s^2$. I am using the ...
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1answer
43 views

How long for released dye to uniformly saturate the oceans?

Suppose a supertanker filled with purple dye breaks open at a particular point in the middle of the Pacific Ocean and spills an enormous volume of purple dye into the ocean all at once. Imagine that ...
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1answer
39 views

Laminar Flow From Outdoor Faucet

I ran across a video recently that really caught my attention. It's been circling the internet over the past couple weeks, but I'm trying to figure out what's going on. Basically, it's a video of an ...
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1answer
33 views

Water / Air flow via thermal difference

This is a simple water/air flow thought experiment I had that I'd like to understand better... The basic idea is that you have a closed loop of water or air standing vertically. One side is heated to ...
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1answer
47 views

Is the velocity gradient of a homogeneous viscous fluid constant?

The formula for the viscosity of a fluid (or even a gas) is equal to \begin{align*} \frac{F}{A} =\mu\frac{du}{dz} \end{align*} where $F$ is the force applied to the top layer of the fluid, $A$ is the ...
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19 views

Why there is a difference between same components of 2 parallel planes?

In this context the author is deriving the net outflow through 2 surfaces.to do so he is calculating the difference between x components ofthe vector V. so now my question is here the 2 surface are ...
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42 views

Shear stress and surface heat transfer rate with various Pr values

I'm revising for my Fluid Mechanics exam, and came across a question that ask us to explain the behaviour of the shear stress and surface heat transfer rate with various Pr values. The question is ...
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3answers
43 views

Question on mass flow and Betz's law

On Wikipedia I was reading an article on Betz's law, where has a statement that lost me: So the density times the area and speed should be equal in each of the three regions, before, while going ...
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1answer
52 views

How can one experimentally measure the velocity of water flowing through a pipe?

I am planning to investigate the effect of bend curvature of a pipe on velocity of water. For this, I will need to find the velocity of water through various pipe bends. Would placing an object in the ...
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3answers
103 views

Strange behavior of water flow

So recently when I was in a toilet, I noticed a strange behavior of the water that flowed down a nearly vertical pipe of my friend house. Instead of flowing straight down on the nearly vertical pipe, ...
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0answers
20 views

How would you model a single point outputting fluid in all directions whilst enclosed in a sphere?

The idea is this: There is a point at the center of a sphere. This point is releasing a fluid (say water) in all directions towards the edges of the sphere. The fluid can collide with the sphere's ...
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0answers
21 views

Difference between von Karman vortex street & shedding

I want to know if there are any differences between von Kármán vortex street and vortex shedding ? If so, what are they?
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0answers
26 views

Levitating water wheel/ball

Recently I have come across this interesting YouTube video regarding this phenomenon. A huge ball is able to be levitated when a part of it is in contact with a water jet shooting upwards. After ...
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0answers
50 views

Proof that pressure rises in a fixed control volume

I am looking for a proof using Bernoulli's equation that that for $Q=(Area)(Velocity)$, $Q_{in}>Q_{out} \Rightarrow P_{inside}>P_{outside}$. I read that for a computer, if the case fans blow a ...
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9answers
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The water analogy seems to imply that power = current. Why is this incorrect?

Many people think of the water analogy to try to explain how electromagnetic energy is delivered to a device in a circuit. Using that analogy, in a DC circuit, one could imagine the power-consuming ...
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1answer
34 views

How to use General Energy Equation in parallel pipes?

My question comes from exercises with parallel pipes such as this. I know that to analyse internal flow, we use general energy equation which origins from the 1st law so each time we apply it we are ...
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0answers
20 views

Finding the Equation for Water-flow Experimentally

I am interested in finding the formula for water flow experimentally. I used different pipes for this. 3 pairs, each pair has two pipes, same diameter, different lengths. The taller one of pipes in ...
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3answers
46 views

Would it generate a lift if wind is circulating inside a nearly closed tube?

For a setup like the below image, would there be a lift generated to the tube, due to bernoulli effect?
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1answer
28 views

Angle of Attack of a propeller blade

What will be the best angle of Attack for a propeller blade that is in the airfoil shape?
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0answers
16 views

Horizontal and Vertical Velocity of point on arbitrary wave profile $\eta = \eta(x,t)$

Say I have for any position $x$ and any time $t$ that I want I know what is the height $\eta$ of an arbitrary wave so that I basically have the function $\eta = \eta(x,t)$ that describes the free ...
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1answer
20 views

Question about Divergence of Disturbance Flow

If we break down a flow past a particle into both the incident and disturbance flow like:$$\mathbf{u}^\infty+\mathbf{u}^D=\mathbf{u}^{total} $$ Can we show that: $$ \nabla\cdot\mathbf{u}=0 \...
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1answer
39 views

Why are the diagonals of the pressure tensor non-negative?

I understand that the pressure tensor is simply the momentum flux which makes sense to me (pressure is force per unit area which is momentum change per unit time per unit area). From this, a simple ...
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2answers
65 views

Combined Poiseuille-Couette flow

I stumbled upon this exercise in James Fay "Fluid Mechanics" book, which I'm using to learn fluid dynamics by my own, and I am struggling a bit with it, any help will be appreciated: The figure ...
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2answers
88 views

How do “divergence” and “curl” relate to the three states of matter?

A fluid is said to have divergence (the ability to flow) and curl {the ability to rotate). Do these two characteristics fully define a fluid, or are there other important properties that I am missing? ...
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0answers
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At what concentration do dispersed particles begin behaving like a fluid?

Suppose that I have a nearly insoluble metallic compound in a solution, and that what little of this compound does dissolve aggregates to form nanoparticles. The number of nanoparticles is ...
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2answers
19 views

Relationship between flow rate and pressure in fire service pumps

I'm trying to get an explanation (at a suitable level please!) for something we have recently come accross. In general in the Fire Service we are taught that if you increase the presure of water ...
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3answers
96 views

What is the shape of a stream of water coming out of pipe?

As shown in the photograph below, when water comes out of a pipe (located on the surface of the earth) it travels downwards in an arc. What is the shape and size of this arc as a function of D, the ...
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0answers
32 views

Doubts in work done in a control volume [closed]

For a control volume, in a general steady state steady flow process, we can write the generalized equation as- \begin{align} \dot{Q}_\text{CV}+\sum\dot{m}_\text{in}\times\theta_\text{in}&=\sum\dot{...
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3answers
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Why does the increase in velocity result in decrease in pressure in a flow? Are there any explanations behind?

So I have been searching for this answer that why would increase in velocity result in pressure drop and found no explanation, please help, thanks!
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1answer
41 views

How fast do the aerodynamic forces on a surface build up?

I`m currently working on my thesis in the field of active car aerodynamics. In order to design a controller to move parts of the cars body I need to know how fast the drag and downforce acting on this ...
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1answer
23 views

Reconciling various expressions of flux and flow in kinetic theory

There are a few expressions I have been shown to describe the flux $\vec{\Phi}_A$ of some quantity $A$ described in kinetic theory. I am having trouble understanding how they are related or if they ...
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2answers
49 views

Pressure distribution around an aerofoil

Some notes that I'm reading right now show a picture of the distribution of pressure around an aerofoil with zero angle of attack. The notes say that the pressure is identical at the top/bottom ...
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1answer
33 views

How does a viscous fluid flow?

In all problem involving viscosity, while applying $f=nA \frac{du}{dz}$ why do we consider velocity of the bottom layer to be zero?
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1answer
43 views

Fluid mechanics

i have seen the following equation of continuity for fluid dynamics for compressible as well as incompressible fluids $\rho_1V_1A_1 = \rho_2V_2A_2$ and it is derived from conservation of mass ...
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1answer
32 views

Airflow velocity and volume loss due to friction

I have a vacuum that the manufacturer claims capable of moving 20,000 cfm of air. In my application we often connect 150 feet of 6 inch diameter, smooth bore, flexible tubing to the vacuum. I know ...
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0answers
60 views

Derivation of the Euler fluid equation

I'm currently taking a class on Thermodynamics where we now briefly touched upon Hydrodynamics. On of the major points of the chapter is deriving the Euler fluid equation and there I found my self a ...
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1answer
72 views

What is the physical meaning of irrotational flow?

I am studying fluid dynamics and while searching on the internet, found many videos explaining the mathematical aspect of rotational and irrotational flow, but i need more clarity on what actually it ...
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Volumetric flow rate between two infinite, horizontal, parallel plates

Two immiscible, incompressible, viscous fluids with different viscosities ($\eta_1$ and $\eta_2$), but same density, are contained between two infinite, horizontal, parallel plates as shown in the ...
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1answer
65 views

What happens to the fluid flow velocity and concentration in a tube that branches out

Suppose that liquid is flowing through a tube with a constant velocity of, say 10 m/s. Within the liquid, there is a constant concentration of some substance, [S], lets say of 20 uM. Then, at some ...
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1answer
72 views

Why textbooks use geometric center/centerline of the pipe when calculating/measuring pressure?

Studying Fluid Mechanics, I started to notice that almost every textbook/website uses a specific point to make calculations about the pressure in a liquid at a given depth (hydrostatic pressure): the ...
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1answer
68 views

Transitioning between Lagrangian and Eulerian fluid variables

I'm having trouble understanding the motivation between wanting to transition between the two descriptions. I figure that switching from Eulerian to Lagrangian fluid variables is useful if we want to ...
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1answer
127 views

Why using average pressure in calculations gives the most accurate results?

In the saga of trying to answer the question that came into my mind while studying the basic concepts of Fluid Mechanics, "Why textbooks use geometric center to calculate hydrostatic pressure when ...
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1answer
59 views

Does the drag equation only apply to turbulent flow

I am doing an analysis of the motion of an object in air and so I'm first finding whether the flow is laminar or turbulent. From my research, I'm still a bit confused as to whether the drag equation ...
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1answer
42 views

How to calculate the power required by a fountain pump?

How can I calculate the power required by a fountain pump, if just the efficiency of the pump, the height of the fountain and the diameter of the water jet is given?
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1answer
60 views

Continuity equation in the Lagrangian flow picture approach

In deriving continuity equations using Lagrangian. We consider the element of fluid which occupied a rectangular parallelopiped having its centre at the point $(a,b,c)$ and its edges $\delta a$ , $\...
3
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1answer
239 views

How is the power of water flowing through a pipe directly proportional to $v³$ and not $v²$?

How is the power of water flowing through a pipe directly proportional to $v^3$ and not $v^2$? (Where $v$ is the velocity of water) I have been trying to write power in terms of $v^3$ but I'm ...
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1answer
29 views

Introducing stream function with given velocity equation

Bit information about the problem We are dealing with the slide coating process - where basically a polymer is being put onto a slot, which is moving in the $x$-direction with velocity $v_0$. The ...
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0answers
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When exactly can the concept of stagnation pressure be applied?

Although I've attached a homework problem here, I'm only using it for reference for a conceptual question on stagnation pressure. From my understanding, in the photo attached above, the pressure at ...