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

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Is it possible that my 750ml water bottle contains spent fuel from a space shuttle launch

Firstly I live in New Zealand which is very distant from USA which is where the space shuttle was originally launched from. So what is the possibility of molecules from the rocket engines spent ...
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42 views

Comparing atmospheric drag in different atmospheres

The book and film The Martian begins with a dust storm on Mars. Is it possible to calculate and compare the effects of a 150mph wind on Mars with winds on Earth? How fast would the wind need to be on ...
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63 views

Streamlines and ideal / real fluids

I was going through some basic description of streamlines in which I noticed that streamlines in an Ideal fluid where shown "equidistant" from each other at a place . whereas in the real fluid ...
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131 views

Streamlines and line of flow of fluid particles

I am very confused with this thing can someone clarify these problems given below-- 1 //Do or can the streamlines of a fluid particle show the position of the particle at a time( using the streamlines)...
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543 views

Why don't surfboards fly out the back of a utility truck when driving on the highway?

I have never had it happen myself and every time I throw my boards (shortboards not malibus) in the back of someone's ute, with no cover on the tray, they always assure me they'll be alright( the ...
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126 views

Air flowing through a duct (pressure drops)

Let's say that I have a duct with the length $ l $ that is connected to a fan, and through the duct there is air flowing with the velocity $ u $. Moreover, let's say we install a manometer right after ...
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78 views

How to derive end-correction value relationship for open-ended air columns?

According to Young and Freedman's Physics textbook, in open-ended air columns like some woodwind instruments, the position of the displacement antinode extends a tiny amount beyond the end of the ...
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30 views

Determine the pressure difference required to drive a prescribed constant volume flux $Q$ through a gap

Determine the pressure difference $P_{1}-P_{2}$ required to drive a prescribed constant volume flux $Q$ per unit width through a gap of thickness $\delta$ of length $L$. To do this introduce ...
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52 views

How does a nozzle behave differently at different velocities of flow?

A converging duct acts as a nozzle for subsonic flows while the same nozzle acts as a diffuser (decelerator) for supersonic flows? How does this actually work?
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134 views

Can Bernoulli fly a car?

I need to settle an argument. How much influence, if any, does the Bernoulli principle have in sending a stock car traveling at 200 MPH sailing through the air when the air pressure unexpectedly ...
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293 views

Clarification on slip, no-slip and no-penetration for incompressible flow

This is my current understanding: The no-slip condition at a boundary means that there is no velocity relative to the boundary, this means that the individual components is zero. So we have (in two ...
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151 views

Simple cylinder fluid mechanics, draining from hole on bottom

So my professor is having us work on an assignment where there is a cylinder full of water with a hole in the side near the bottom. Given the use of stopwatch, balance beam, beakers, etc, how can we ...
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29 views

Are these reasonings about tides correct?

This is a picture of the "M2 tidal constituent": The nodes corresponds to fixed points, for which the moon has no influence on the altitude. 1. Static VS Dynamic problem? I was first wondering if ...
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61 views

Continuum fluid theory

It is written in this article: http://www.maths.ed.ac.uk/~yktsang/4520/basic_fluid.pdf "In the continuum model of fluids, physical quantities are considered to be varying continuously in space, for ...
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77 views

How to model the mixing of two fluids?

In the context of a research project of mine, I am faced with the difficult task of modeling the mixing of two fluids in a container. I would like to achieve the following: Given a container (...
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278 views

Why the units of surface tension are force per unit length?

I do not understand surface tension concept. I read explanations from many sources but I still do not get the units that it has. The units of surface tension are $N/m = J/m^2$. Let's define the ...
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70 views

Fluid parcel + point of a fluid

If we have a fluid(Static or dynamic), and for example we pick a point in this fluid. This point is represented by a very small cube (or small volume). Inside this cube, it has the same properties (...
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134 views

How are the turbulent spectra determined in relativistic turbulence?

In a non-relativistic compressible fluid, the turbulent energy spectra are well-understood and appear to follow the Kolmogorov hypothesis. It would also appear that relativistic turbulence also ...
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448 views

Why do hot tubs dehydrate you? [closed]

I was just sitting in a hot tub for a few hours with friends, and we all noticed we really wanted to drink some water. We felt dehydrated. I tried looking up why hot tubs dehydrate you and all I got ...
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603 views

How can the atmospheric pressure be different in distinct points at the same altitude?

From an hydrostatic point of view, the pressure in a fluid should be the same at the same depth/altitude. Obviously, in our atmosphere that does not happen. I am guessing that the main reason is the ...
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70 views

Bernoulli principle and particle

Bernoulli principle describes the flow of a fluid for steady, incompressible flow along a streamline. But it is said for a particle of a fluid along a streamline. My question is a particle of fluid ...
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112 views

What do the differences between spatial and temporal spectra imply about the structure of turbulence?

In the study of turbulence (theoretically, computationally and experimentally), we often appeal to Taylor's Hypothesis, which (very loosely) summarized means taking measurements at one point in space ...
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264 views

Fluid mechanics assumptions

I have just started studying fluid mechanics and on the very first page two assumptions are made about liquids while I understood the first one but am not able to understand the Second one //" parts ...
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Speed increase in a ventrui relative to its initial speed

Does the air speed through a ventrui reach a higher final speed if its speed prior to entering the ventrui is higher than if it entered the same ventrui with a lower speed? I should add that the ...
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44 views

Angular momentum transfer in a bottle vortex

A colleague and I were discussing the following fluid mechanics experiment, which most people have probably tried in their kitchen: take a bottle full of water (a 2-litre transparent soda pop bottle ...
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133 views

Water bombing - risks and possibilities

I just saw a video on youtube, where an excavator drops a load of water on a car, destroying it completely. I also saw a video with a fire-fighting plane dropping even more water on a burning truck. I ...
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122 views

How to calculate gas flow/permeation through solid metal membrane

Given the absolute pressures of air on both sides of a titanium membrane of known thickness (0.1mm) and diameter (3mm), how would one calculate the rate of gas exchange/escape through the titanium ...
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78 views

What does $\mathbb{R}^3$ and $\mathbb{T}^3$ look physically for the Navier-Stokes equation?

What does the Navier-Stokes equation solution according to the Clay Math Institute look like in real life? As in how do you visualize $\mathbb{R}^3$ and $\mathbb{T}^3$ without the math? I actually ...
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101 views

I disagree with the definition of Reynolds number. Why am I wrong?

My question is about the intuition behind the Reynolds number. For example they say that if a fluid is moving 1 10 mph past a sphere of radius 10m with viscosity v 2 100 mph past a sphere of ...
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45 views

Falling then rising of an effervescent tablet dropped into a glass of water [duplicate]

If you drop an effervescent tablet into a glass of water. The tablet first sinks to the base of the glass and effervesces energetically - producing a rising column of bubbles, i.e. a bubble plume - as ...
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21 views

Should cohesion be considered as a resistant force here?

In some droplet generators, a pressure pulse is applied on top of a liquid reservoir connected to a nozzle and FIRST, a liquid jet is emerged from the nozzle and THEN, pinch-off of a droplet will ...
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58 views

Why does rolling down opposite windows create a breeze?

If, while driving, I roll down both of the front windows an inch or two, it mainly creates some turbulence around the window. By symmetry we shouldn't really expect anything different. However, if I ...
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70 views

Would a propeller underwater have thrust?

The type I mean is the ones on aircraft. Do the same physics apply with a propeller underwater?
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106 views

Bernoulli equation as an energy conservation equation

I don’t want to learn and apply Bernoulli's equation. It is complicated and you need to remember a lot. I instead want to apply energy conservation. But I don't always find it easy. For example, when ...
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229 views

How to calculate thrust from opening a pressure vessel in space?

One popular trope in science fiction is the astronaut who (deliberately or inadvertently) punctures an air tank or something and goes rocketing off. How would we calculate the amount of force that ...
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152 views

Pressure variation

Imagine we have a vertically orientated pressurised liquid filled closed pipe. The pipe is shaped like a spring, such that the distance between the two ends can be adjusted vertically, whilst the ...
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93 views

If pressure in fluids is caused by the elastic collision of fluid molecules then why does the pressure increase with depth?

We know that pressure in fluids increases with depth but why does it happen, if pressure is caused by the collision of particles?
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147 views

Htting the brakes with a pickup truck full of water

I am looking to settle a bet. My friend and I were discussing truck bed pools, which are pick-up trucks with their beds tarped and filled with water converting them into small temporary swimming pools....
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137 views

Calculating Reynolds number of ellipse in fluid

I know Reynolds number is calculated from the formula by including length or diameter of an object in fluid. I have a case where there is ellipse with 2a major and 2b axis. I hv learnt when the ...
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33 views

What is the difference between hydraulic radius and geometrical radius in a cylindrical pore?

What is the difference between hydraulic radius and geometrical radius in a cylindrical pore? I was going through the 'stacks' present in an thermoacoustic refrigerators there I came across the ...
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96 views

How is the pressure of an incompressible fluid measured?

I've googled around and can't find quite what I'm looking for.. this may be a VERY basic question, but I'd appreciate if it could be explained in layman's terms.. Traditional fuel injection engines ...
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184 views

Must-know topics for Computational Fluid Dynamics (CFD)

My undergrad major was Electrical Engineering. My MS thesis is related to simulation of hydrogen movement in a complex geometry. I did take a course on Fluid Dynamics but I have to say it wasn't one ...
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48 views

How long can water hold elevated pressure and energy after opening pressure cooker lid?

I noticed today that the water warmed up in pressure cooker (1.5 ATM) dissolves sugar much faster and much more than water cooked in 1 ATM. I am interested in how long can water hold the high ...
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196 views

Is there a theoretical limit to the maximum flow through a pipe?

Assuming laminar flow, the Hagen–Poiseuille equation defines the flow rate as a function of the head pressure. However as the flow rate increases so does the head loss due to friction within a pipe, ...
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238 views

Angular velocity of a fluid element

If we have a fluid element that is subjected to: Translation Rotation Extensional strain (dilatation) Shear strain As in this picture starting from time $t$ it can be shown that angles $d\alpha$...
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Is there a formulation for (self-)accelerating fluid flow through permeable medium?

I have a permeable system where is an accelerating fluid flow. Imagine a sponge that is squeezed. The fluid starts at rest, accelerates and flows out from the sponge. How to calculate the fluid speed? ...
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Approximation for rotational drag on a box?

The drag equation gives us an approximation for the drag on an object caused by its velocity in a fluid: $F = \frac{1}{2} \rho A v^2 C_d$ Is there any similar approximation for the rotational drag ...
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159 views

How do shock waves form in space?

Today my aerodynamics professor mentioned that the equations we were learning for atmospheric shock waves can also be applied by astrophysicists to study black hole-related shock waves in space. How ...
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Funnel theory exists?

I have a funnel and I notice when I try to pour powdered sugar through it, it blocks up unless I tap it. If I put sand in the funnel, it goes through. Is there a theory of funnels that can predict ...
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Is there a dynamic prelude to the state equation?

If I'm not mistaken, the state equation $$PV=nRT$$ also known as the 'ideal gas law' serves as a mathematical model relating pressure-volume-mass-temperature states of an assumed ideal gas. In other ...