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Questions tagged [flow]

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

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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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How can the velocity field $V_z$ be obtained with this equation? [on hold]

I need to obtain the formula for the velocity field between 0
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35 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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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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1answer
22 views

Volumetric Flow with Air Compressor [on hold]

If I have a 5 gallon, 125 psi air compressor and I connect that to a pvc pipe with holes in it, how would I go about determining the amount of air flow through each hole in that pipe. It might be ...
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24 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 ...
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27 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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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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3answers
50 views

Please explain airflows above and below aerofoils for a layman

I have read about the lift of aerofoils a lot recently and just want a few things cleared up. When incoming airflow hits a typical cambered aerofoil and diverges into "top" and "bottom" airflows, 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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25 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
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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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2answers
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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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1answer
47 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
53 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
55 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
58 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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1answer
50 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{\...
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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
30 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
67 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 ...
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4answers
58 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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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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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 ...
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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 ...
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1answer
56 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
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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
34 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
30 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 ...
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2answers
133 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
59 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
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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
63 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
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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
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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
33 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
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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 ...
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1answer
28 views

Two containers that have the same volume (let say 500 liter) but are different in shape

I remember from school, one time a teacher explain us the following: two containers of the same volume, but one is thin and tall, and the second is short and wide. then if we fill them with water from ...
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2answers
120 views

Continuity equation, differential form vs integral form in 1D flows

The continuity equation for fluid flow assuming steady-state and constant fluid density, that is: $\rho = \text{constant}$ and $\partial_t=0$ can be written in the two following forms (differential ...
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2answers
90 views

Why does the flow of charge even create electricity? [closed]

Okay this is a question I’ve asked a lot of places but I always get its the flow of charges and it’s like a property. What I don’t really understand is how is this flow of charges creating electric ...
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38 views

Air pressure drop off rate

I’ve been thinking about this for a while, and at first, I assumed that the inverse square law applied, but seeing as how air isn’t a form of radiation, I’m not sure that it still applies. So if we ...
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Heat transfer in Steady vs Oscillating flow through a Matrix material (Conceptual Input needed)

I have been trying to model heat transfer and pressure drop for oscillatory flows inside a closed channel flowing past a matrix material. My intuition and experimental results (in journal papers) tend ...
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2answers
55 views

Pressure in a moving fluid

I’m having some quite large conceptual difficulties which I hope can be resolved by considering this example. When considering the pressure in the sheet very far away from the impact zone the ...
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1answer
54 views

Heat flow for an ideal gas in Isothermal Expansion

I'm having a bit of difficulty grasping the concept of heat flow in isothermal expansion -- most likely because I don't fully grasp the concepts yet. We were given a problem that the professor ...
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3answers
93 views

Why is blowing so different than sucking? [duplicate]

Why is it so easy to blow out a candle from a significant distance, but nearly impossible to suck enough air to do the same? Even without focusing the airflow through a nozzle or something, this ...
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1answer
37 views

Unclear assumption in deriving fluid energy conservation laws

I am currently working through Alexandre Chorin's Mathematical Introduction to Fluid Mechanics. In the first chapter, he treats the change in Kinetic energy of a fluid region $W\subset D$ subject to ...
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0answers
61 views

Pressure buildup in a pipe

How to model the fluid's pressure evolution over time and distance in a pipe, from inlet to outlet, assuming the fluid is water. Say that I have a pipe filled with a fluid with pressure P1 and ...
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1answer
64 views

What is a precise definition for laminar flow that includes “laminar vortex-shedding”?

I can't find a definition for laminar flow that includes vortex structures. See paper: Numerical calculation of laminar vortex-shedding flow past cylinders and countless others when googled.
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Bernoulli Experiment, unanswered questions

In the bernoulli experiment, the pressure on one side is greater than the other, thus the fluid flows faster through the thinner nozzle.In the image, is the pressure created shown correctly? Since ...
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2answers
111 views

Potential flow pressure on a smooth surface

For an incompressible potential flow around a smooth rigid body, is it true that the pressure on the surface of the body is proportional to $a\cos^2\theta+b$ where $\theta$ is the angle the inward ...