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Questions tagged [flow]

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

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3
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2answers
68 views

What is irrotational flow? How to judge?

For example, when the wing moves horizontally, the direction of fluid flow changes first to upward at the leading edge of the wing and then to downward at the trailing edge. Does it rotate? If the ...
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0answers
35 views

calculate CFM of a ceiling fan

I'm trying to calculate, or even understand what data do i need to calculate the CFM of a ceiling fan. in many countries this is a given data in the product details but not where I'm from. I have the ...
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0answers
18 views

Acoustics air flow vs the human body

My question to you all is... Is it possible to move air acoustically. ie to move air over a 2.1m distance to be felt by the human body with a cooling effect but not heard by the human ear ? I'm just ...
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0answers
91 views

Problem estimating the flow rate in natural draft chimney using Bernoulli equation including heat and friction losses

I am trying to build a simple model for fluid flow and heat transfer in a natural draft chimney. I've found some literature about it (most of them giving the same result as the equations on the ...
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1answer
50 views

Why does blood pressure drop when blood vessels rupture?

Some people say that because the flow is large, the pressure is low. Is that right? Why does the pressure drop when the flow rate is high?
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1answer
31 views

How to measure flow rate using Toricelli's law?

For my experiment, I want to investigate the relation between height and velocity using Torricelli's law. I would like to know how I would measure the flow rate from volume in a spouting cylinder.
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62 views

Viscous losses in loop helical flow

Imagine flow of the following kind. The flow line for each flow particle is a helix with its axis bent so that the beginning attaches to the end. How can I determine the viscous losses in this flow ...
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3answers
110 views

Do drones fly because of low pressure above them or high pressure below them?

I was working on some drone battery life solutions and was stuck with the question whether drones fly because of low pressure created above them by the rotor or due to high pressure created below them....
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0answers
50 views

A doubt on this paper regarding Ricci flow on space-time

https://arxiv.org/abs/1812.06239 In this paper,the authors use ricci flow to construct Lifshitz spaces. But it is known that ricci flow is limited by Riemannian manifold, which has a positive metric....
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17 views

Macroscopic hydrodynamics, is there a fluid “vacuum” force?

Background I was looking at the following simulated fish movement article and how the physics could be improved (ie, made more realistic) with out a huge impact on performance. It looks like they ...
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1answer
144 views

Is it correct for me to understand why air moves along a curved surface?

As shown in Fig. 1, water flows horizontally from A-A section, and it flows along the surface under the action of gravity. As long as the velocity is not high enough, the water will not leave the ...
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2answers
181 views

What does the pressure term in Bernoulli's equation signify?

Consider the Bernoulli equation of fluid dynamics. One of the terms is $p$. I know it is pressure. But what type of pressure is it? Is it pressure due to height or a completely different concept?
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1answer
38 views

Bernoulli's theorem in water flow through a burette

Consider a burette (like the one in a chemistry lab) with uniform cross-section and open at both ends so that they are exposed to the atmosphere. Once we open the stopcock/plug (P in the diagram) the ...
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0answers
20 views

Surface refresh rate

How does one determine the refresh rate of a fluid in the following example: A laminar flow of a certain (lets say 10 ml/hour) volume/time of a certain fluid goes along a certain surface area (lets ...
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1answer
87 views

Bernoulli's equation's contradiction

Using Bernoulli's equation P Pressure p density V velocity of fluid $$P_1+ \rho gy_1+\frac{1}{2}\rho V_1^2 = P_2+\rho gy_2+\frac{1}{2}\rho V_2^2$$ $$V_1^2-V_2^2 =\left(2g(y_2-y_1) +\frac{2(...
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0answers
17 views

Does a rubber pipe bears more weight when the pressure of water inside it is high?

I have passed a rubber pipe across a road to my home temporarily. The pressure of water inside the pipe is very high, the vehicles and school buses passes over it! i am interested to know that "In ...
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2answers
98 views

Can Bernoulli's theorem be applied to laminar flow?

Since in streamline flow the velocity of a particle at any point is same, Bernoulli's theorem can be applied to streamline flow, but could it be applied to laminar flow?
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36 views

Non-viscous incompressible Fluid between two coaxial cylinder

Consider a non-viscous incompressible fluid lies between two coaxial cylinders. The domain occupied by the fluid is defined as $0<z<\xi$, $A<r<B$. The coaxial cylinders slowly rotate ...
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47 views

Air Flow through non-uniform size Duct with Holes

We are a manufacturing plant and this is one query which we could not find the answer too. So, came here asking for help. Problem: In the attached image, you can see the air/steam inlet from the top ...
3
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1answer
54 views

Is a hole better for ceating a toroidal vortex than a pipe?

Does a hole work better for creating a toroidal vortex, where the fluid starts to turn as it exits, than a pipe, where the flow inside is more laminar. Some high power vortex guns have a cone shaped ...
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0answers
25 views

Frictional losses in flexible tubing with multiple branches opening up to a large tank

I am working on designing an experiment where I will be creating a wall-jet flow where the wall is a rotating wing. After some thought I realized I need to estimate the pressure losses due to the pipe ...
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4answers
114 views

Please explain airflows above and below aerofoils for a layman

I have read about the lift of airfoils a lot recently and just want a few things cleared up. When incoming airflow hits a typical cambered airfoil and diverges into “top” and “bottom” air flows, why ...
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0answers
16 views

Bubble flow in vertical pipe

I have an application where I would like to keep a bubble flowing freely within a pipe. Assume a single small, spherical, non-deforming gas bubble in a viscous, laminar fluid flowing in a vertical ...
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0answers
26 views

Is it possible to create an ongoing vacuum?

This is a crazy thought but here goes. We all know about creating a vacuum in a jar but it is feasible to create a continuous vacuum or low pressure to reduce drag by dispelling or otherwise creating ...
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1answer
55 views

Interpretation of critical points (or sonic points) in fluid flows

In the study of transonic flows in astrophysics, we come across critical points (also known as sonic points) where the fluid velocity equals the velocity of sound. Across such critical points, a ...
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2answers
44 views

How to calculate pumping pressure for backfilling of a borehole?

I am trying to calculate the pumping pressure needed to backfill a borehole with geothermal grout. The hose is pulled up at the same rate as the borehole fills, so pumping pressure will get lower as ...
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1answer
202 views

Bernoulli's equation in system of coupled tanks

Problem statement. Consider a system of two coupled tanks as the one shown below Several authors such as Bistak and Huba, 2014, Sim et al, 2017, Khalid and Kadri, 2012, Essahafi, 2014 claim that ...
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1answer
115 views

Flow equation for system of coupled tanks

Consider the following system of interconnected tanks: The two tanks have cross-section areas $A_1$ and $A_2$ respectively and the levels of the liquid are denoted by $h_1$ and $h_2$ respectively. ...
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1answer
62 views

Why is the rudder of a ship shaped like a wing?

I don't understand why lift gives an advantage, it could be working the same even if it was just flat.
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1answer
156 views

How to find drag of a cylinder?

How can I find a drag on the cylinder placed in uniform water flow, if I know a velocity field around it?
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2answers
191 views

Convective derivative vs total derivative

I was wondering what is the difference between the convective/material derivative and the total derivative. We were introduced to the notion of material derivative $$ \frac{D\vec{u}}{Dt}=\frac{\...
2
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0answers
131 views

Can you explain the perfume bottle with the Bernoulli effect?

Someone explained the perfume bottle with the Bernoulli effect: squeezing the bulb over the fluid creates a low pressure area due to the higher speed of the air, which subsequently draws the fluid up. ...
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1answer
36 views

simple gas flow between regions

How does gas flow between regions of differing pressures? How does the momentum of the gas effect that flow between regions of differing pressures? I am trying to program a simple simulation of gas ...
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1answer
73 views

Is it correct to use Bernoulli's theorem to explain that a disk floats in the air? Should the correct explanation be based on Boyle's law?

In this video, a device is introduced from 1 minute to 18 seconds. After entering the air, the disc at the bottom of the device will be suspended in the air. The video explains that this is because of ...
2
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4answers
72 views

How can I calculate the speed at which a gas flows from one volume to another?

Suppose that there are two rigid Volumes A and B. Each of these contains a gas with know properties (pressure, temperature, number of moles, volume, composition). Suppose also that there is a pipe ...
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0answers
71 views

Gas Flow Between Two Pressure Vessels

I am trying to determine the volumetric flow rate between two pressure vessels at different pressures and volumes. Nitrogen gas is stored in a K bottle at 2640 psi (P1)and 3045 in$^3$ (V1). The tank ...
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2answers
70 views

Replace warm air with cold air

In summers i.e. now, my room has hot uncomfortable air in night,but outside air is cold 4-5 degrees Celsius colder than inside, my room has windows parallel to wind flow, so though wind flows in night ...
2
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5answers
216 views

Why can water be sprayed farther when the pipe outlet is narrowed?

Someone told me: This is because the flow rate remains unchanged, so the flow rate of small diameter pipelines is faster. I don't think this explanation is right: the diameter of the pipe outlet is ...
0
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1answer
99 views

Can Bernoulli Equation be applied across two fluids?

There is a beaker with two liquids placed above another. The beaker has a hole at bottom. So can I use Bernoulli equation across the interface of liquids.
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2answers
117 views

Complex Potential describing inviscid fluid flow

I'm a Mathematics student, working through a homework sheet for a Fluid Mechanics module. The question is given: Consider the flow described by the complex potential $$w=4z+\frac{8}{z}.$$ ...
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2answers
37 views

Which way does the fluid flow? [closed]

In the given siphon arrangement if a hole is made at D, will water leak out or will air leak in? I think air should leak in as fluids flow from high to low pressure but I'm not sure... Any help ...
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1answer
31 views

Potential Flow integration (no-voice and very beginner!)

Let's say I managed to compute a velocity field that is divergence-free. How do I integrate it over time? meaning, I created a potential function, set v to be curl of potential function, so I have now ...
3
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2answers
168 views

How should energy loss in a hydraulic jump be calculated?

The energy loss in a hydraulic jump is still calculated with the old equation of Bresse from year 1860; (I.e., equation 7 in this paper from 2017) $$ \frac{\Delta E}{E_1} = \frac{(\sqrt{1+8Fr^2}-3)^3}...
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1answer
106 views

Why does the flame of a gas stove not spread backwards?

On lighting a gas stove the flame is active only above the burner. However, the gas input from beneath the burner and all the way to the pipeline contains gas fuel. Why doesn't it all ignite up ? I am ...
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2answers
169 views

How pressure and velocity is related? And its effect in cavitation

As per my knowledge I think when velocity increases and discharge is constant,the fluid(liquid) molecules get away from each other in the region where velocity is high and that's why they get ...
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1answer
65 views

Bernoulli Experiment- why is the pressure on the left greater? [closed]

Is the Pressure $P_2$ caused by a reaction force to the fluid-fluid collision, or is it the result of the collisions of the water molecules with the walls at the neck of this experiment. The part ...
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1answer
47 views

Energy balance in a thermodynamic system

I think I've missed this point in class but I was wondering how to determine for example if I have a turbine, the Energy balance would look something like this: $W$ as work $h_1$ as intake and $h_2$ ...
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1answer
45 views

Expression of mass flow rate for steady flow

According to Wikipedia the mass flow rate is given by: $${\dot {m}}=\iint _{CS}\rho \mathbf {v} \cdot {\rm {d}}\mathbf {A}$$ And using the Reynolds Transport Theorem (if there is no sources): $$\...
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1answer
42 views

Streamlines equation in a fixed frame

In this wikipedia article about potential flow around circular cylinder, the stream function is given by: $$\psi =U\left(r-{\frac {R^{2}}{r}}\right)\sin \theta \tag{1}$$ But in another article we ...
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2answers
84 views

What causes my “kitchen witch” to move? [closed]

Not a physics person but curious about something going on and hoping someone can explain. I have a kitchen witch hanging from my kitchen ceiling on some fishing line and it’s constantly swaying and ...