# Tagged Questions

The quantitative study of how fluids (gases and liquids) move.

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### How the flow is distributed when the water flow from one river/drain to multiple rivers/drains?

Assuming that water ( total amount $Q$) flows down from one river/drain, into multiple rivers/drains, under the action of gravity, as shown below: How the flow ($Q$) will be divided among different ...
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### Why the meandering ratio of river different from different study?

Referring to this question Is the meander ratio of a river $=π$? According to the accepted answer, based on a paper by Leopold and Langbein The resulting curve is not quite a semi-circular curve,...
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### Would a hybrid mixed medium balloon allow you to use less helium to lift equivalent weight?

Suppose you had two balloons, one inside the other (a inside b). Would filling balloon "a" with the 80% nitrogen/20% oxygen mix you find in the surrounding air at ground level, and then filling ...
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### Example of basic(?) fluid dynamics [closed]

I am completely new to the world of fluid dynamics, I have tried to come up with what I hope will be a simple case. How does one go about calculating the following? I am far more interested in the ...
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### Resonant frequency(s) of system of resonant objects?

I am trying to gain a better understanding of resonance when we are dealing with a coupled system of resonating objects. For example, say we have a single gas bubble in liquid and suppose it ...
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### What causes fizz?

When you go to a soda fountain and pour some soda into your cup, frothy fizz is generated at the top of the cup. What causes this? Obviously has something to do with carbonation, but when my cup is ...
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### How do I find a stream function given a volumetric flow rate?

How do I find a stream function given a volumetric flow rate? The flow only occurs in one direction, between 2 plates, and I have no knowledge of velocity. I know that volumetric flow rate = ...
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### External v.s. internal Reynolds number for cylindrical pipe

When calculating Reynolds number for cylindrical pipe, we were taught: $Re=vd/\nu$, where $v$ is the fluid velocity, $d$ is diameter, and $\nu$ is kinematic velocity. If you reorient the cylinder so ...
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### Why does wind sound the way it does?

You can obviously hear wind. From everyday experience, the stronger the wind, the louder its sound. But this sound is always similar, and quite distinctive, noise-like. Can one compute the spectrum ...
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### Normal Modes for Standing Waves in 1-D Acoustic Ducts with Arbitrary (but real) Impedance Jumps

Let's say we have a 1-D duct, such as this: Where $Z_i \equiv \frac{P}{US}$ is the acoustic impedance, L is the length of the duct in question, and S is the area of the cross-section. In general, ...
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### Pulse wave velocity

I heard that the pulse wave velocity is higher than the speed of blood flow through the arteries. This is obviously due to the ellastic properties of vessel walls. I would like to have the most ...
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### Derivation of Kelvin's circulation theorem

In the derivation of Kelvin's circulation theorem, I take the material derivative of circulation, or \begin{align} \dfrac{D\Gamma}{Dt} = \dfrac{D}{Dt}\oint_C \vec{u} \cdot d\vec{\ell}. \end{align} ...
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### What is the force exerted by a fluid on the corner of a right-angled tube? [closed]

It is to be considered that the water is entering and leaving at the same velocity v. I have found a solution but cannot understand it as it is using a term dM/dt which I cannot understand in this ...
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### Is surface tension characteristic of a fluid?

Does surface tension depend only upon the nature of the fluid or on other factors too like the liquid-solid or liquid-gas interface? I saw in my book definition that $$S = U/A,$$ where $U$ is the ...
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### Entropy in ideal fluids [closed]

Can you derive a conservation law for entropy per unit mass? I know that there is a proof for this conservation. My assumptions are: $(\nabla p)/n = D \vec{v} + \vec{v} \cdot \nabla\vec{v}$ (Euler ...
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### How many water wheel can fit on a river until another one produces zero energy?

Mostly what I'm after are the factors I need to know to do the problem. Imagine we're in the days of Leonardo Da Vinci. And pizza is everyone's favorite food. And there's a river that goes on ...
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### Would a Tesla Valve create a pressure differential?

Start with two sealed boxes that are the same in every way. Then connect them by a tesla valve so that air could flow between them. Over time through entropy would the one-way preferential flow of ...
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### Reconciling the Temperature and Pressure Relationship in Gasses vs Fluids

I've been trying to wrap my mind around this for the last couple of days to no avail. I suspect that much of my confusion comes from the fact that I have not yet taken a class specifically focused on ...
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### reynold's transport theorom contradicting bernoulli equation

I am considering a funnel with two areas $A_1$ and $A_2$ with velocity at the interface as $V_1$ and $V_2$ respectively. let pressures at those areas be $P_1$ and $P_2$ . For simplification we assume ...
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### If I Blow smoke out my window, will any come inside my room?

My girlfriend and I have got into a lively debate about whether or not my flatmates can smell the smoke I blow out my window. Can you help us? Here is the scenario. The smoker, places himself ...
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### Total energy of the fluid

Consider a one dimensional system with fluid in it. Mass and momentum balance equation of the system are (in the absence of external forces and assuming Newtonian behaviour valid for viscocity), \...
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### What is the definition of governing equation? [closed]

What is the exact definition of the governing equation? What is its purpose? What makes it different than other equations of physics? Why they are necessary?
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### physical constraints on fluid models based on shannon entropy/information

Is it possible to use the idea of entropy to constrain mathematical objects meant to describe physical fluid motion which is virtually incompressible and virtually without friction. More precisely ...
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### Drag in Free Fall [duplicate]

I was recently thinking about how I might go about describing projectile motion with air reistance. The problem I encountered was that air resistance might cause some acceleration for a short period ...
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### Mathematical understanding of vortex solitons

I am wondering if anyone has ever come up with a mathematical description of something that (to me, and I am no expert) look like soliton vortexes. The example I can think of is if you create two ...
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### Diffusion (2 species) versus advection (1 species)

Why do we see diffusion with 2 species but advection with a single species if both cases involve molecules spreading to increase entropy? To take a physical example: Let's say I have a box with two ...
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### Velocity of water column

If an air filled tube 5 km long with a diameter of 20 m was submerged vertically under water one end 5 km underwater and the other end at the surface, how fast would the water column rise if the ends ...
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### When I open a window to air out the room, how does the smell disperse?

Let's say I'm in a room with some kind of noxious stink, possibly of flatulent nature. The quickest way to right the world that comes to mind is to open a window. When I open a window, how do the ...
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### What is the use of thermal boundary layer and velocity boundary layer?

In heat transfer by convection, why must we show the thermal boundary layer and the velocity boundary layer. What do they signify? Also how are these terms related to the Prandtl number? And what is ...
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### How does submerging tubing affect 'airflow' when the tube is filled with water also?

The question probably isn't asked well and I feel sort of stupid asking it but... So I have a small piece of tubing connecting two chambers (where both the chambers are partly filled with water and ...
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### What is the “flow area” for a screen/mesh? [closed]

I'm trying to find out, for a given duct area, how large an area of woven mesh (like bug screen) do I need for minimal pressure drop? Is there a rule of thumb or approximation for "effective flow ...
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### Flow in a cylindrical pipe

A cylindrical pipe is, at the left of section A, divided by a plane passing through its axis. The upper half is supplied with water at a velocity $V_1$, the lower half is supplied with water at a ...
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This is not intended as a realistic way for propulsion of submarines, it is just an interesting thought experiment. Say I want to travel directly towards the wind, only powered by the wind. This is ...
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### Relativistic blast waves in medium of non uniform density

The relativistic outflow of a gamma ray burst drives a shock into the circumburst medium. This medium could have a uniform density $n_0$ or a density profile of the form, $n(r) \propto r^{-2}$. For ...
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### Acceleration of an bubble under the sea [duplicate]

An air bubble arises from the bottom of the sea. Find its acceleration if resistance force is proportional to $\rho Av$ where $\rho$ is density of water, $A$ is cross section area and $v$ is velocity ...
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### Navier Stokes : what about angular momentum?

I play with CFD for a while, and suddenly, a transcendantal question raises: :-) Navier Stokes is basically Newton applied on a continuum in Eulerian. For solids, we would consider linear, but also ...
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### Origin of spin and direction in the magnus effect

If you solve the Bernoulli equation: $$p=p_0-\rho_0{v^2 \over 2}$$ using a complex flow potential for a flow around a cylinder: $$W(z)=v_0 z + {v_0 R^2 \over z} - {\Gamma \over 2 \pi } \ln(z)$$ you ...
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### Is there a difference between solid-to-fluid convection and fluid-to-fluid convection?

I found an online calculator relating to convective heat transfer, but the calculator's description says it's for heat transfer between a solid surface and a moving fluid. However, the definitions I'...
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### Why do stellar boundaries exist?

What theorems or insights are available to decide wether a star with some given interdependence between its density, pressure and temperature distributions ought to have a boundary at a finite ...
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### Physical intuition for Lamb vector

In many aerodynamical descriptions involving vortex structures (e.g. the Crocco's theorem) there is a useful physical quantity called Lamb vector: $$\vec{\omega} \times \vec{v}$$ where \$\vec{\...
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### Liquid jet in the absence of gravity [closed]

On earth, we have liquid jets which are falling and accelerating under influence of gravity ( this cause their radius to decrease ) My question is about liquids in the absence of gravity. Can we make ...
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### Changing the Density of a liquid while its surface tension is constant

I'm working on Plateau-Rayleigh waves and I want to investigate the effect of density of the liquid on the wavelength of these waves How can I change the density of the liquid while its surface ...
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### How to restict air flow without reducing pressure

I have a large volume of lightly pressurized air say 10000 cubic feet at 1 psi above atmospheric pressure. I want to move it to another area through a duct which is 20 in by 20 in. Airflow will be ...