Questions tagged [flow]

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

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32 views

Why does the wind close doors?

Assume you have two rooms, both with holes in the wall (more commonly known as open windows), which connect each room to the exterior. The two rooms are connected, but the connection can be closed by ...
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Is there a Coandă effect outside the atmosphere?

For example, when air is blown through a spoon in the atmosphere, the air flow bends toward the spoon. People say it's the Coandă effect. So, outside the atmosphere, when we let air blow through the ...
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How to avoid water tension in a hose?

I am doing a project in which I have to flow water between two containers, which are connected at the bottom by a 1/4" hose. Remarkably, the surface water tension is such that water does not flow ...
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39 views

(SOLVED) Calculate the velocity of a gas inputted in pressure difference

I'm trying to make a generally simple calculation but I'm not sure if I'm approaching this correctly. So as I'm making assumptions solving this problem, please comment or correct me wherever I'm wrong ...
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How can you calculate the total time taken for water to completely flow out of a container given the amount of water initially in the container?

I'm doing an experiment on changing the amount of water in the container and seeing how the time is taken changes with it. The container has a little hole at the bottom where the water flows out from. ...
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Can the flow be irrotational if the viscous forces act on fluid?

I tried to answer the question only using the definitions and the Navier-Stokes equation: $$\rho \frac{Dv}{Dt} = -\nabla P +\rho g -\mu[\nabla \times(\nabla \times v)] $$ In my opinion if the ...
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35 views

Flow in parallel vertical pipes

Consider a tank open to atmospheric pressure, with a large cross-section area A1 and height H, that contains an incompressible fluid. Two vertical pipes with length H and cross-section area A2 are ...
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Relationship between pressure, chamber volume, and flow rate? [closed]

It has been a while since I took any classes involving fluid mechanics, so bear with my phrasing. I am trying to pump water using a peristaltic pump (Masterflex C/L) with tubing that has about a 1 mm ...
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Does density vary with time in a steady flow?

Steady flow is defined as the type of flow where density, pressure and velocity don't change with time, as far as my understanding goes. However, in the video below, they say that the density in a ...
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1answer
24 views

Physical meaning of the convection term in the momentum equation of acoustic wave

In deriving the acoustic wave equation, the momentum equation is used. $$\frac{\partial \mathbf{u}}{\partial t}+ (\mathbf{u}\nabla)\mathbf{u}=-\frac{1}{\rho} \nabla p$$ Intuitively, the convection ...
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176 views

Conversion between Power and Flow rate of Fan taking into consideration the geometry of the fan

I need to find the relation between two properties of a fan, that is between power and flow-rate. I expect such a formula to depend on the pressure and on the geometry of the fan. I have found in ...
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71 views

Grad student needing help with a fluid mechanics issue in project

As the subject states I have hit a wall in a fluid mechanics associated problem in designing an experiment for my grad project. Long story short, I'm an engineering undergrad who got a broad ...
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Specific total enthalpy VS Specific enthalpy

What is the difference between specific enthalpy and specific total enthalpy in the context of fluid flow?
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Does laminar flow of a mixture tend to result in mass separation?

In a laminar flow regime, a fluid separates into streamlines with a parabolic flow profile. Do particles within such a flow tend to become aligned by mass (e.g. lighter molecules travelling together ...
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26 views

Most effecient negative shape to create laminar flow

I was looking at laminar flow filters to aid in my mycology work I'm doing. Most filters use an aluminum extrusion with fins. I figured the options out there are pretty expensive for what you get and ...
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Wich is the correct flow rate $Q$ solved with iterations?

I have a little question about this problem I computed the right answer this way First I applied Bernoulli between the top and the exit $$\frac{P_{t}}{\rho g}+z_{t}+\frac{v_{t}^2}{2g}-H_{1}-H_2-H_{\...
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Flow velocity ambiguity in transition region

I have calculated the following short table concerning the stationary flow of water in a 1 meter long pipe with a diameter of 16 mm and a completely smooth inner surface. The flow is driven by the ...
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$Gm/r$ in momentum equation of compressible flow for cylindrical geometry

In the case of compressible flow, due to the gravitational field, the source term added in the momentum equation (which is gravitational potential) is $Gm/r$ in the case of cylindrical geometry and $...
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Flow in bend pipe

What happens to a flow in a bent pipe of uniform cross sectional area? Will there be any change in flow velocity at the outlet? If yes, why does it happen? What happens at the bent area of the pipe? ...
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What is the shape of the upper boundary of water hitting a screen?

When I saw that thing I did not understand how that shape is formed? To be ideal, take a vertical smooth plane. Now aim at the wall with a thin water tube. Then the outer layer forms a "parabolic ...
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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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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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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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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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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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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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61 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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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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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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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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115 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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174 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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27 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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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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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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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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Adiabatic and isothermal astrophysical flows

Astrophysical flows around black holes (like accretion and winds) can be adiabatic as well as isothermal. In adiabatic flows, the flow is non-dissipative except at the shock location. However, in case ...
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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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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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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 ...
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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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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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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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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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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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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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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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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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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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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.