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

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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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38 views

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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302 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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27 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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84 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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102 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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32 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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132 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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145 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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1answer
761 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 ...
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1answer
67 views

Does charged saltwater repel itself?

if you take a volume of saltwater, and charge it to a high voltage, will the water molecules repel each other and climb the walls of the container slightly, or does the fact that water is polar ...
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110 views

How does a 1,000 mph car maintain vertical stability with tiny front wings?

Formula 1 cars have wings to help keep them on the road during cornering, they don't need them whilst moving in a straight line. And that's ok , they "only" travel at 220 mph. In a different speed ...
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123 views

How does a ball cause a splash? (With the relevant math)

Problem Statement: Imagine a spherical ball is dropped from a height $h$, into a liquid. What is the maximum average height of the displaced water? For instance, although one particular drop of water ...
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276 views

Crown shape in water waves?

Watching this slow motion video of waves caused by a droplet falling on water, I am puzzled by the first wave shape. The first wave rises with circular symmetry as I expected, but is not even in ...
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1answer
159 views

Forces of reaction and torque of water flowing out of a vessel

Consider the problem wherein we are told to find out the force of reaction of water flowing out of a vessel through an orifice. I attempt to compare it with a shotgun and a bullet as a conservation ...
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34 views

Calculating the 'splash zone' of a water droplet?

How would you calculate the probabilistic area for a water droplet splash zone? So far my guess would be to find out how much the wind is acting upon it horizontally, find out how fast its falling, ...
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134 views

Coffee Straw Physics

When I put my little, cylindrical coffee straw into my coffee, the liquid immediately rises about half a centimeter up the straw without provocation. This is also the amount of coffee that the surface ...
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1answer
73 views

Perturbations on a fluid thread and hydrodynamic instability

I know that due to fluid instability there are some perturbations ( picture below ) after all of these, my question is the reason of existence of these perturbations. Why exactly they appear? Shear ...
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137 views

Fluid speed and fluid density

How does fluid density affect fluid speed? Basically I am trying to figure out if, with all other quantities remaining constant, would an increase in fluid density cause the fluid speed to ...
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3k views

How can fast moving particles gain energy from slow moving ones?

Imagine a large diameter piston filled with water connected to a small funnel. When you press on the piston slowly but with considerable force the water will move very quickly from the funnel in form ...
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75 views

growth rate of the instability of a laminar flow?

I was just studying something about The Plateau-Rayleigh Instability that I saw something called Growth rate of the instability. My question is the exact physical definition of growth rate of ...
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366 views

What happened here in this Taylor-Couette Flow experiment?

I came across this video of Taylor-Couette Flow on YouTube. Originally I was looking for a visualization of the wavy Taylor vortices induced by the angular motion of the inner cylinder. However, I ...
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44 views

Maximum pressure in a die-less wire drawing apparatus

I ran across this patent: http://www.google.com/patents/US4549421 and was interested by the idea of reducing the cross sectional area of a wire with only shear stress caused by the wire being pulled ...
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51 views

Will there be a drag for a solid body already dragged due to reaction?

By learning Fluid Structure Interaction tutorials, I managged to simulate a 2d transient fsi simulation using Comsol fsi fully coupled module. A solid body due to motion in vertical direction ...
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1answer
100 views

Why in fluid interface, liquids tend to reduce their surface?

I've read something about fluid interface and know that liquids tend to reduce their surface but my question is that why do they tend to reduce their surface?
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98 views

How to calculate maximum wind speed in a funnel (Venturi Effect)?

It must be in an open area, so nothing forces the wind, just himself. Lets assume that the wind is blowing only one direction. I assume that at some point the speed will stop increasing and it will ...
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76 views

What law of physics did these people think they disproved?

I was trying to understand the Physics of how water gets to the leaves of a tree and found this article which claims some experiment disproved a 300 year old law of Physics. Sounds pretty unlikely... ...
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What does air “feel” like to a flying mosquito in terms of viscosity?

If I go for a walk at, say 4 km/hour, unless there is a breeze blowing, I probably won't notice the air around me at all. If I go for a swim though, I will immediately notice the viscosity of the ...
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113 views

Stationary waves on a laminar liquid flow near collision with a surface [duplicate]

Look at the picture below I know about plateau rayleigh instability. And my opinion is that the reason of this phenomena is plateau rayleigh instability. But there's a question, in the picture ...
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181 views

How do hydrofoils tack without a keel

I asked a while back about how sails produce a forward force on a boat and got some good answers and (I thought) a good understanding: essentially the sail produces a force that has some non-zero ...
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1answer
129 views

What is the difference between flow and expansion?

Fluids (both liquids and gases) will move from one point in space to another due to a potential gradient. Some examples may be: 1) horizontal pipe flow, a fluid will move from a region of high ...
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302 views

Question Regarding torricelli's theorem/Law

I recently studied about bernoulli's equation/principle. After the derivation of the said equation , my book gave some applications of the principle, which include torricelli's theorem/law. In ...
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547 views

Can solids behave like liquids?

Basically, the more I look at things the more it seems like there's entirely no difference between a liquid and gas, it all just depends on the relative density of what's around it. This being said, ...
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75 views

conservation of energy for a viscous fluid

I have a pair of questions about conservation of energy and momentum in a viscous fluid. First, energy. Symon's Mechanics states an equation for conservation of energy in a droplet of a non-viscous ...
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83 views

volumetric flow rate due to Bernoulli's principle

for calculating the volumetric flow rate of a liquid coming out of a tube, I know that If the pipe is too short, the Hagen–Poiseuille equation may result in unphysically high flow rates; the flow is ...
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Which travels further, a football or a soccer ball, when thrown?

I recently answered this question: Laminar Versus Turbulent Flow and it caused me to think of the following situation. Given that an (American) football weighs between Football 400 to 430 grams, and ...
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115 views

Unsteady and incompressible flow

In scientific literature, we know that the condition for incompressible flow is that the particular derivative of the fluid density $\rho$ is zero: $$ \frac{D\rho}{Dt}=0$$ and for steady flows the ...
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63 views

Why is temperature a function of $y$ and $t$ only?

Say you have an incompressible thermal conducting fluid contained between two infinite horizontal plates separated by a distance $H$. Initially both the plates and the fluid are at rest at ...
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83 views

Why small droplet goes upward after pinch-off?

This small droplet moves against gravity. How to calculate its initial upward velocity exactly after pinch-off?
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51 views

total vorticity generation in 3D

In 2D flows, the total vorticity generation for an impulsively started plate can be found by measuring the circulation of the flow. This gives the vorticity generated per unit length. I would like ...
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129 views

Why are racing catamarans' hulls not teardrop shaped? [closed]

Looking at the America's Cup 72 class catamarans, I was wondering about their hull shape, which has a sharp wave piercing bow. My question is: since an airfoil shape experiences less drag than a sharp ...
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230 views

Shaken vs stirred, is there a difference? [closed]

I was looking up tequila Drink recipes for the up coming holiday, and I kept seeing ones calling to be shook and other to be stirred. So I wondered: is there really a difference? does stirring provide ...
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582 views

Height of Water 'Splashing'

Suppose from a height $H$, I throw a ball of mass $M$ and radius $R$ with initial velocity $u$ into a pool of depth $x$ having a liquid with density $\rho$ and coefficient of viscosity $\eta$. ...
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87 views

If the surface tension is reduced to half(say by using a surfactant), what would be the effect on the size of an air bubble in the liquid

If I reduce the surface tension to half of the original value, what would be the effect on the size of an air bubble in the fluid? What would be the effect on buoyancy and drag forces? Also, if I ...
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1answer
100 views

Find the separation distance for a line of oil being squashed between two flat plates [closed]

I was wondering if someone could give me some help on how to start this problem, I'm really struggling to get my head around it. A long line of oil is being squashed between two flat plates of length ...
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1answer
68 views

Efficiency of a gravity feed hose

If I am trying to fill a large cylindrical container with a gravity feed hose, would it be more efficient, time-wise, to drill a hole in the bottom of the container for a greater initial pressure ...
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3answers
1k views

Why does a sheet of paper fall slower than the same when rolled into a ball?

It depends on volume but both the sheet and the sphere have the same volume. Does surface area play any role here?
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2answers
144 views

Show that the boundary layers diffuse out from the plate with speed $\sqrt{\frac{\nu}{t}}$ [closed]

I was wondering if somebody would be able to help me with this problem. I know how to solve it using dimension arguments but I'm unsure what is meant by transformation techniques. Any help would be ...
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1answer
306 views

Why can't it work? Perpetual motion machine [duplicate]

Lets assume that the red ball is more dense than the white fluid and less dense than the blue fluid. The fluids are of very low viscosity and the machine can be of any height. The flaps open when ...
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269 views

How deep can a whirlpool descend?

My question is based around comparing the physics of a tornado against, what I imagine/assume to be the marine equivalent of a tornado, that is a whirlpool located either at sea, in a tidal region or ...