Questions tagged [flow]
The motion of fluids (gases, liquids and granular material).
-1
votes
0answers
22 views
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 ...
-2
votes
0answers
30 views
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 ...
0
votes
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 ...
4
votes
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 ...
1
vote
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 ...
0
votes
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 ...
0
votes
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 ...
0
votes
0answers
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 ...
0
votes
0answers
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 ...
0
votes
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 ...
0
votes
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 ...
3
votes
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, ...
0
votes
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 ...
0
votes
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?
1
vote
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 ...
2
votes
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 ...
20
votes
9answers
6k views
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 ...
0
votes
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 ...
0
votes
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 ...
2
votes
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?
-1
votes
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?
-1
votes
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 ...
0
votes
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 \...
1
vote
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 ...
1
vote
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 ...
0
votes
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? ...
1
vote
0answers
22 views
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 ...
0
votes
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 ...
4
votes
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 ...
1
vote
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{...
-1
votes
3answers
40 views
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!
4
votes
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 ...
1
vote
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 ...
0
votes
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 ...
-1
votes
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?
0
votes
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 ...
0
votes
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 ...
0
votes
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 ...
0
votes
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 ...
-1
votes
0answers
32 views
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 ...
0
votes
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 ...
1
vote
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 ...
2
votes
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 ...
0
votes
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 ...
0
votes
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 ...
-1
votes
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?
2
votes
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
votes
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 ...
0
votes
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 ...
1
vote
0answers
32 views
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 ...
