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

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9-point stencil “equivalent” for advection equation

So I inherited from some people a code that solves the advection-diffusion-reaction equation for a particular system. The original code was first implemented in 1D which worked fine in cartesian ...
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1answer
64 views

Landau's Ideal fluild one dimentional flow equation

There is a similar Phys.SE question here, but I still didn't get the idea. The problem is: Write down the equations for one-dimensional motion of an ideal fluid in terms of the variables $a$ and ...
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110 views

What is the cause for turbulence?

The transition from laminar flow to turbulent flow is usually told interms of Reynolds numbers. The Reynolds number is $Re=UL/\nu$ where $U$ is the speed, $L$ is dimensional length and $\nu$ is the ...
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58 views

Viscosity, bubbles and (super)fluids

3-part question, but I think it's simple enough... Does the tendency for cavitation in a fluid depend on its viscosity? If so what does this imply for superfluids, having 0 viscosity? And for that ...
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80 views

Why and how strong are currents near ship side?

I read reports of people drowned swimming in rivers near medium-sized boats or flat-bottom barges. The idea is that an anchored ship stands still, and the surface current (which goes exactly along it ...
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28 views

Pressure gradient - derivation for air stream

I need help clarifying the statement made here that $$dp = l\frac{dp}{dx}$$ $\frac{dp}{dx}$ is an infinitely small change in pressure at some point x. $dp$ is the total change in pressure between ...
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83 views

How does fluid velocity affect the dissolution of some solute in the fluid?

Suppose we have a perfect sphere of some solute such as sugar and we place it in a fluid such as water, at a certain temperature, that is not moving. It will dissolve and diffuse into the water due to ...
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41 views

Why is there a pressure drop across a Kaplan turbine?

The Kaplan turbine is an inward flow reaction turbine, which means that the working fluid changes its static pressure as it moves through the turbine and gives up energy. But how does this pressure ...
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2answers
107 views

What's wrong with this argument that aerodynamic lift really does rely on Bernoulli? [duplicate]

There is a grade-school explanation of how a wing works that goes approximately like this (although I'm leaving out an erroneous bit): Because of the geometry of the way the wing meets the air, ...
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1answer
165 views

When an object plunges into water, what is the maximum height a droplet from splash can reach?

I cleaned up the kitty litter just some minutes ago. When I threw the products of our 7kg cat into the toilet bowl, the broth splashed and one drop went straight into my eye. yuk. Here come the ...
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5answers
204 views

No diffusion term in conservation of mass in Navier-Stokes equations?

I have followed derivations of the Navier-Stokes equations and I can see how the various terms arise in the "main equation", the momentum conservation equation. However I don't understand why the ...
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38 views

Slow sustained liquid movement in a vacuum

Can water or any other liquid be made to “simmer” or “low boil” (slow sustained liquid movement) in a vacuum as opposed to go from liquid to all out boil when the vapor pressure is equal to the ...
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68 views

Does a whirlpool(vortex in water) continue in air(vortex in air),and when does a vortex stop?

First part: The question is both about the continuity of the water vortex(whirlpool) to vortex in air in time and in space. About continuity in time,does the vortex of the water slowly produce a ...
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3answers
265 views

How does the area of an open window affect airflow?

This question stems from a disagreement between me and my girlfriend. During the hot summer months, we like to open up the windows during the early morning to cool down our flat a bit. One of us ...
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1answer
38 views

What is the Proper way to determine overall velocity in a pipe?

I am running a simulation of fluid in a pipe. The fluid in this pipe is "swirling" (instead of just moving in one direction, it's rotating as well. Like the Helix below. The fluid is faster on the ...
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1answer
539 views

What is the cause of the surface tension of the liquids? [duplicate]

What is the cause of the surface tension of the liquids? How to know the direction of tension force on the free surface of the liquid? I know that the surface tension is the force acting normally ...
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0answers
49 views

Sriarcha, Shampoo and Unexpected Trajectories

Some time last year my parents-in-law related to me a story which rang true in my scientific brain. They had gone out to see a show, and then decided to go to a fancy Asian restaurant. One course ...
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1answer
96 views

What is the maximum speed of an object moving trough air? [closed]

While seeing the comic Flash I wondered what could be the maximum speed of a invulnerable human being (like Allen) running through air on the surface of the Earth? At what speed would its surrounding ...
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2answers
97 views

Will the water go inside the moving water bottle?

Let's say that there is a empty bottle in the water moving at a high speed like this: My question is: Will the water go inside the the empty bottle when the bottle is moving at a high speed? If ...
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24 views

Measurement of compressible flow velocity

Assume that you have a pipe with known volume fow rate $\dot{V}_1$ and pressure $p_1$ on the first point. You use an ideal gas as fluid. We derived in our script a formula for the case that you ...
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1answer
37 views

drift velocity of gas needed to get into a pressurised vessel

Would a gas entering a narrow tubular opening of an initially empty vessel at a given velocity, fill up the vessel to a definite pressure? If so, how is the velocity of the gas related to the final ...
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2answers
193 views

Is there a simple equivalent to Ohm's law for gas (pressure=R*throughput)?

Question I have the feeling gas cannot have an equivalent of Ohm's law, tying pressure and throughput via some kind of fluid resistance constant depending on the geometry of the obstacle considered. ...
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1answer
83 views

Does a venturi injector contradict the 2nd law of thermodynamics?

The picture below shows a venturi injector. When the water flow enters the narrower cross section its velocity increases and its pressure decreases. Subsequently, fluid is sucked (or injected) into ...
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1answer
37 views

What granular/colored material suspends itself in an enclosed container filled with water regardless of pressure, gravity and buoyancy?

i've been looking around for an answer but it turns out that google dsn't think it's an obvious question. Would really appreciate the help. Basically i'm wondering if there is any known material that ...
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1answer
181 views

Worthington jets explanation: fluid phenomenon

I don't understand the reason behind the formation of Worthington jets I've been reading a bit about Worthington jets Video 1, this phenomenon is caused when something is thrown to the water as we ...
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1answer
60 views

Fluids Dynamics - Transmission Oil Dilution Problem [closed]

I have a fluids dynamics (I guess) problem with my car and I can't seem to find the answer: I have to change my transmission oil. It has a 7 liter total capacity, but due to the torque converter, I ...
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98 views

Symmetry considerations in Plane Poiseuille Flow

I'm taking a first course on fluid dynamics, and I have this (sort of) conceptual question that's been nagging me for a moment now. I can completely follow the mathematics behind the derivation of the ...
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3answers
154 views

Why are vehicles not pitted like golf balls?

I have read that non-laminar flow reduces drag on blunt bodies. Given that, why is pitting not used on motor vehicles?
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1answer
37 views

Water well fluid dynamics [closed]

In my home village everyone has their own water well at the foot of the mountain (limestone) . The wells are over 100 feet deep but they are not cemented or have the area between the hole and the ...
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2answers
116 views

Is this a case of the “venturi effect”? What's behind the “Venturi effect” actually?

Some dinghy sailboats have a hole in the bottom of their deck used to automatically bail out water after a capsize. bailer of the laser sailoat The mechanism only works if the boat is moving. The ...
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1answer
77 views

2D aerofoil fluid analysis - find velocity ratio

I just wondered if you could help me out on this fluid mechanics question? I have worked through it myself but am very unsure of my answer (not yet found the pressure difference) the question is ...
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0answers
50 views

Alternative to Naphthalene Sublimation

I work in a wind tunnel that uses Naphthalene for flow visualization. Specifically we use it to see the location of transition from laminar to turbulent flow. We mix it with acetone and spray it on ...
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2answers
96 views

How does a Venturi Injector comply with energy conservation?

How does a Venturi Injector comply with energy conservation? When the water flow enters the narrower cross section its velocity increases and its pressure decreases. When the pressure gets lower ...
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0answers
86 views

Question about Elon Musk's Hyperloop Suspension [closed]

So one of the proposed suspension systems that will be used on the hyperloop include the externally pressurised air cushions. These cushions lift (or atleast help lift) the capsule and reduce drag ...
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64 views

Cleaning a dirty jar [duplicate]

I would like to wash the inside of an almost empty cylindric jar on whose walls there are remains of a sticky substance such as peanut butter. I do this by filling it up with water and then shaking ...
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0answers
38 views

Sedimentation at the bottom of a vessel

At the moment I'm studying the sedimentation of suspensions. There is a lot of literature discussing the physics behind this processes (e.g., 1, 2, 3, 4). Most of the sources I found study only the ...
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25 views

Flow Rate Calculation from a drain tank through a pipe [duplicate]

I want to know how to calculate the flowrate (Q) of a drain tank flowing through a pipe (see the figure below) All I know is that Q=Velocity(V) x Area (A) V= sqrt(2*g*H)=sqrt(2*9.81*10)=14m/s. I ...
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Why can't the Navier Stokes equations be derived from first principle physics?

At the 109th UCLA Faculty Research lecture, Seth Putterman gave a talk on Sonoluminescence. During the lecture he emphasized that "The Navier Stokes equations cannot be derived from first principles ...
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3answers
85 views

Why do the tangent holes (like in pitot-static tube) feel the static pressure?

Why do the tangent holes (like in pitot-static tube) feel the static pressure although the static pressure is in the direction of the velocity of the streamlines not normal to the surface of the hole
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85 views

Pressure - How much fluid can void support?

Please refer to the attached (terrible) drawing while reading the post ! After watching some videos about the U-tube effect in drilling, a question came to me. Imagine one fluid of heavy density ...
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35 views

Specific form of Stokes's differential equation

Coming from a chemical background, I have next to no knowledge of the (as it seems to me) complex field of fluid dynamics, so bear with me here. I'm reading a paper written by seismologist Norman ...
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1answer
74 views

Frictionless and inviscid

In the book Fluid Mechanics by Robert A. Granger, there is a study question, 4.10, asking "How can frictionless real fluids exist and inviscid fluids not exist?" Could someone please explain? ...
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3answers
351 views

Why dont we consider force exerted by atmospheric pressure in mechanics?

My school has started teaching fluid mechanics, and it really bugs me why we don't consider force exerted by atmospheric pressure in mechanics. I couldn't understand a word my teacher said. There is ...
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1answer
101 views

Forces of suction in WIllie Wonka's Chocolate Factory (filmed 2005 starring Johnny Depp) [closed]

Before I begin the question: I am in no way judging this movie, just happened to be casually watching it and saw the scene (referred to below) and thought to post this question. The scene: Boy falls ...
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3answers
337 views

Direction of pressure forces on a control volume (surface)

According to http://www.mne.psu.edu/cimbala/Learning/Fluid/Pressure/pressure_basics.htm, "Pressure always acts inward normal to any surface (even imaginary surfaces as in a control volume).". ...
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1answer
713 views

Terminal velocity of a steel ball in water [closed]

I am investigating on the terminal velocity of steel balls moving in water. I used the balls with different diameters, such as 3.17mm, 6.02mm, etc. And I used a full-filled 1L graduated cylinder. I ...
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1answer
92 views

Would a linear relationship between pump speed and the flow rate from the pump be expected?

I am building a water cooling system for my pc whereby the water can be individually redirected to each of the three individual graphics cards depending on temperature. Can the relationship between ...
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1answer
38 views

Weather Meridians

Are there meridians that effect cloud movement? While observing radar images of moisture bearing cloud movements (at my location in Florida), I've noticed a splitting of the cloud formations a ...
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2answers
85 views

Why does simmering sauce make bubbles and how Is it different from boiling water

Why does simmering sauce makes bubbles at different places. Is this like boiling water? Why or why not?
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374 views

The optics of vortex (in water): why there is a bright ring?

This picture is from this YouTube video from "Physics Girl", which shows how you can generate vortices in a swimming pool by using a plate: And there she explains the creation of the shaded circle ...