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

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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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88 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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32 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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20 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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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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54 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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85 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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134 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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113 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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69 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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112 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 ...
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65 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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25 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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63 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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121 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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42 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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105 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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106 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 ...
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43 views

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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28 views

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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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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59 views

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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75 views

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 ...
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119 views

How is viscosity related to the forces in fluid?

I think it was that the forces are only perpendicular but do not know how this is related and from where it comes from. EDIT: I am asking for the difference between viscous and non-viscous fluid in ...
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164 views

Can we regard dark matter as a special fluid rather than individual particles?

If we assume that dark matter is an $N$-body system of sizeless and collisionless particles which only interact via newtonian gravity, do these huge quantity of particles manifest some collective ...
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while travelling in a bus or train, air comes inside the vehicle but it seems it goes nowhere

I have been amazed observing that while travelling in a train or bus , we feel air comming into the vehicle. I know this is due to difference in pressure but my question is that we dont feel air going ...
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157 views

Turbulent and smooth flow of water from a tap

When water flows normally from a tap, we can say it is turbulent ( Pic 1 ). But when we attach a piece of cloth to the opening of tap, water flow becomes smooth ( Pic 2 ). We can say that by touching ...
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movement of water in plants

Books say that water moves from places with a high water potential to places with a low water potential. The movement of water in plants are explained because water potential is lowest in leaves and ...
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328 views

Can water be made to flow through a pipe using only gravity and resulting in a higher elevation at the end of the pipe from its starting point?

I am not a physics guy, so be nice to the layman, guys! Please note: not a homework type problem. This is a scenario being considered for real-world application. I have not yet considered details ...
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50 views

How do cyclonic dust separators work? [closed]

I have a background in engineering so I am somewhat embarrassed to say that I don't understand how a seemingly simple cyclonic dust separator works. Here is a link to video of such a device in ...
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66 views

Sound in stirred hot fluids

If a hot beverage in a cup gets stirred, the sound of the spoon changes. You can easily hear this if you repeatedly cling the spoon to the cup ground after stirring. The cling sound will raise in tune ...
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115 views

Stokes law in 2-dimensions

Stokes' law states that force on slow moving sphere (i.e. $Re\ll1$) in liquid is $$ F_d = 6 \pi \mu R V $$ In two dimensions we are in trouble (flow around disk in 2d or around cylinder in 3d), ...
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Pressure as a scalar? [duplicate]

Why do treat pressure as a scalar? We know that $P=F/A$ (Pressure = Force/Area) and force is vector quantity, so then why should pressure not be a vector?
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Problems implementing Lattice Boltzmann method

I want to make a basic 2D implementation of the Lattice Boltzmann method (in javascript) to simulate gas/fluid flow, but I have run into some problems and I can't seem to find the cause of it. ...
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64 views

Balancing a bowl of water

Let's say you have a mildly elliptical bowl balanced on top of a stick. This bowl is filled with water, not necessarily to the top but fairly full (I'm not 100% sure this makes a difference). You then ...
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77 views

Velocity of water from tap to fill a cracked bucket to brim

Let us consider a real life situation. The bucket in figure below (drawn using MS PAINT) has an irregular crack of essentially small area. And I decide to open a tap above it and start filling it ...
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197 views

Bernoulli's Equation for flow of gas and changing area

My task is to determine the size of piping needed in a system. In this system, hydrogen gas flows horizontally in a $\frac{3}{4}\,\mathrm{inch}$ pipe and into a vertical pipe of a larger diameter. My ...
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Is it possible that any spatial variation in press disturbance without gravity?

When gravity (and buoyancy), acting as the only body force of a liquid, is ignored. Is it possible that any spatial variations in pressure perturbation are the result of fluid motion or some other ...
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87 views

Why velocity potential?

(Aero-)Acoustics (among other parts of fluid-dynamics) loves the velocity potential $\varphi$ defined as $\vec{v} = \nabla \ \varphi$ with the condition of $\nabla \times \ \vec{v} = 0$. I am ...
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63 views

Centripetal forces acting on fluid flow in a bent pipe?

Yesterday I answered this question, using analysis of forces from this web page. But today I started having doubts regarding the completeness of this analysis. It occurred to me this approach does ...
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How to visualize that the critical flow conditions in a heat added flow remains constant?

In a variable area nozzle, where compressibility is observable, if the flow goes from point A to point B and heat addition is considered. How do we see that the critical speed of sound (imaginary ...
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Can we tune the exhaust system of a gasoline car to be as quiet as an electric car? [closed]

Electric cars are quiet, so quiet that legislation is proposed in many countries, to make them audible to pedestrians, for obvious safety reasons. My question: is it possible, without getting into ...
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139 views

Force applied to a 90 degree elbow by hydraulic flow

I have a question about forces applied to a 90 degree elbow. Essentially we have a 90 degree pipe bend used to redirect discharge from a water system, which can discharge high volumes and pressures ...
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26 views

Help me in the measurement of small deformation of a gas-liquid interface

I am new to optical measurements and sorry for any stupid question? I am also not sure whether this is a right place to discuss the experimental issues... Recently, I am trying to measure the small ...
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81 views

Equating $\frac{dp}{dt}$ and $F$ at a hydraulic jump?

A journal I am reading about circular hydraulic jumps provides the equation and I quote: $H$= Depth after hydraulic jump, $h$= depth before hydraulic jump, $V$= velocity after hydraulic jump, $v$= ...
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92 views

Is the reason why water in a cup rises if a solid is placed within it the ideal gas law?

Let's say you have a cylinder with water that takes up volume V and has temperature T. When a solid mass is placed within the cylinder, the water momentarily takes up a smaller volume within the ...
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26 views

fluid dynamics of two streams in single pipe

Background: The fetus needs to deliver both high and low oxygen tension blood within the same pipe (inferior vena cava) back to the right atrium. Blood entering the right atrium is able to cross an ...
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72 views

How does a water-steam mixture behave?

Namely, if I mix a flow of steam that has density $\rho_s$, velocity $v_s$, and pressure $P_s$ with a flow of water that has pressure $P_w$, velocity $v_w$, and density $\rho_w$, how can I find the ...
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113 views

Lift and drag coefficients on other planets

The question I'm trying to answer seemed simple: how hard would it be to fly on a planet with lower gravity but also thinner atmosphere compared to Earth. If the answer could hint me at how much ...
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626 views

can gasoline be compressed

Simple question, can gasoline be compressed? Is it compressible as in how water is incompressible. Would one be able to store x gallons of gasoline in a pressurized container that is x-y size. For ...