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

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Incompressible Navier-Stokes pressure solve in simulations

I am a complete newcomer when it comes to fluid simulations. I'm currently working through some tutorials to understand the idea of of the discretized Navier-Stokes equations for numerical simulations....
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89 views

Fluid mechanics -Question about boundary?

Problem statement: A two-dimensional fluid stream of thickness $S$ and velocity $c$ (evenly distributed through the thickness of the stream) falls on a stationary plate and gets separated. Calculate ...
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1answer
168 views

Equation of a water pump with a nozzle

If I have a small water pump with a flow f (L/s) and maximal pressure p (bar) and attach its output to a small tube having on the other end a nozzle with an area A (m^2). What is the equation that ...
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64 views

Paradoxical Friction When Frying Eggs

I cook scrambled eggs for breakfast in an 8-inch diameter non-stick frying pan with sloping sides (approx 45 degrees). I cook the eggs in a lot of butter and bacon grease that is melted firest, so ...
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2answers
107 views

Heating suprecritical water in a closed water tank

How does the pressure of water in a closed tank evolve in the following setting: - closed tank of 2 liters (filled up with water) - water initially at 25°C and pressurized to 3 bars The water is now ...
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1answer
162 views

In a fluid, why are the shear stresses $\tau_{xy}$ and $\tau_{yx}$ equal?

In solid bodies, $\tau_{xy}=\tau_{yx}$ makes sense to me because the volume elements "hold together" and can not spin against each other and therefore the resulting torque from the shear stresses has ...
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199 views

Confused on how to apply the volume integral form of the Biot-Savart law

In Viscous evolution of point vortex equilibria (Jing, 2011) the author explains that the velocity equation for the Lamb-Oseen vortex is found by applying the 2D Biot-Savart law to the vorticity ...
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40 views

Can water seep in?

Today morning I was sweating a lot, and a drop of it directly fell on my iPhone's home button. Considering the height of fall to be approx. $30 cm$, I started wondering whether water could seep in. ...
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6answers
2k views

Why is a beam reach the fastest point of sail on modern sailboats?

I've heard that a beam reach (perpendicular to the wind) is the fastest point of sail on modern sailboats, but I haven't heard a satisfying explanation of the physics behind the claim. Triangular ...
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0answers
145 views

momentum equation to find velocity of solid particle after collision [closed]

If a particle collides with a liquid drop, particle might penetrate into drop and so the velocity of particle reduces. i.e. a sudden change in particle velocity happens right at the collision moment, ...
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1answer
148 views

Effect of small changes in atmospheric pressure on open cylinder piston

OK, I'm not a physics student, but I played one for 2 semesters 35 years ago... now I'm a competitive shooter working a theory about why small changes in atmospheric conditions cause our hyper-tuned ...
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0answers
20 views

Increased pressure of Liquid Pitch and Limestone (Bitumen/Asphalt) @ approximately 300 degrees Fahrenheit

If liquid pitch and limestone (20/80 mostly limestone) is pumped (appx. 5 gpm) out of a nozzle that restricts the flow compared to the flow that would be achieved straight out of the pump ( no ...
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1answer
168 views

Finding velocity field of spherical bubble in incompressible fluid

I have the following question: A spherical bubble in an incompressible fluid of density $\rho$ has radius $a(t)$. Write down an expression for the velocity field at a radius $R > a$. The pressure ...
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1answer
96 views

Nozzle vs Orifice Water Jug Draining

why is this happening? Water jug draining So why does the water drain faster when you drain a jug through a funnel compared to the hole you make at the bottom of a jug( the hole is the same size as ...
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1answer
69 views

How do compressible fluids behave near a sink?

Imagine there is a large spherical tank of a fluid floating in space. There is a small pipe from the outside to the inside that opens in the center of the spherical tank and lets fluid out at a ...
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0answers
856 views

Flow rate Calculation with Pipe Diameter and pressure?

I am using a constant Diameter pipe from a motor to a machine for oil flow.A pressure trasmitter is kept near the machine to know the pressure.So can we calculate the Flow rate using the parameters ......
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46 views

Pool full of Jell-O

Imagine I have filled my backyard swimming pool (8 feet deep) with a solid block of Jell-O. What would happen if I tried to swim in it? My understanding is that the viscosity of the "water" doesn't ...
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3answers
1k views

Is Torricelli's law “wrong” for big holes? - Tank draining problem

Consider a tank full of water with a constant cross-sectional area A1 placed vertically on the ground. Now someone drills a hole of an area A2 in the bottom of the tank, and the liquid starts escaping ...
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1answer
301 views

Perfect fluid and Cauchy momentum equation

The stress-energy tensor of a perfect fluid is given by $$T^{\mu\nu}=\left(\rho+pc^{-2}\right)u^\mu u^\nu+pg^{\mu\nu}$$ The divergence of the stress-energy tensor is zero: $\nabla_\mu T^{\mu\nu}=0$. ...
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0answers
113 views

Why Does Moving a Cup of Coffee Up and Down whilst carrying it Make it less Likely to Spill?

Sometimes I have a Very Full Mug of Coffee and I am trying to carry it without it spilling. I noticed that if I moved the Mug up and down when carrying it, it seemed to settle the coffee and make it ...
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0answers
51 views

Fluid flowing into small pores

I have some open porous foams with pore sizes ranging from 50-100nm. I want to flow water into this structure but even at 30 atmospheres it would NOT go in. I am looking for a way to calculate the ...
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0answers
43 views

$L^p$-weighted enstrophy calculations

Mathematician here, only somewhat familiar with physics, but finding myself involved in a research project on fluid dynamics. I'm studying a 3D simulation of turbulent fluid flow, and we are currently ...
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37 views

What is a diffusionless fluid?

I'm taking a course in astrophysical fluid dynamics and have come across a problem involving "small diffusionless disturbances" of a fluid. Based on the nature of the course I expect the examiner to ...
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2answers
216 views

What is the curve described by the water of a wet spinning tennis ball?

I'm looking at this picture from this site and I'm curious about what is the curve described by the water. The involutes $$x=r\left[\cos(\theta+n)+\theta\sin(\theta+n)\right]\\ y=r\left[\sin(\theta+...
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0answers
39 views

Volumetric flow rate as a function of radius of pipe [duplicate]

I have a container (assume open on top) with $1m^3$ of water. That water exits this container from an opening that has a cross-section area A e.g. $πR^2$ = $1cm^2$. What is the volumetric flow rate ...
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1answer
113 views

Applying unsteady Bernoulli (to a balloon attached to a tube)

Using Bernoulli’s equation for an unsteady irrotational motion of an inviscid incompressible fluid, solve the following: Water of density $\rho$ is driven through a horizontal tube of length $L$ and ...
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1answer
200 views

Bernoulli Equation for isentropic ideal gas flow

If one derives the Bernoulli Equation for the isentropic ideal gas flow you get: $$ \frac{1}{2}v^2 + g z + \left(\frac{\kappa}{\kappa -1} \right) \frac{p}{\rho} = const. $$ Two questions: Is ...
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2answers
2k views

Why bodies lose heat faster in water than in air?

A simple question. In several places, including this very recent and already famous paper http://www.sciencemag.org/content/348/6236/786.short it is stated that bodies lose heat in water very fast ...
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1answer
89 views

Meaning of imaginary eigenvalues in advection equation

I'm reading the book Fluid Simulation for Computer Graphics (Amazon link), and stumped by the following sentence in Chapter 3: what's happening is that the eigenvalues of the Jacobian generated ...
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1answer
633 views

Solve unsteady state Bernoulli equation for flow in a pipe

I am an engineer studying an unsteady-state flow through a pipe. The Pipeline has been cleanly cut into two halves, without deforming the cylindrical form of the pipe, exposing the contents to ...
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0answers
107 views

Viscous drag proportional to $r$ or $r^3$?

When a spherical object is falling at terminal velocity through a fluid: $W=U+F$, where $W$ is weight, $U$ is upthrust and $F$ is viscous drag. Rewriting, using Stoke's Law, we get: $$\frac{4}{3}\pi r^...
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1answer
44 views

Ocean surface mean current flow meaning

I tried to simulate the trajectory of an drifting object in the oceans by using the data of the OSCAR project http://www.oscar.noaa.gov/. The dataset actually used consist of grid sampled mean 2d ...
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1answer
53 views

Finding volume of water that emerges from opening per unit time [closed]

A rectangular opening (width w and height h2-h1) is cut into the side of an open tank. The water doesn't emerge in a uniform velocity. Assume that SA of tank >> area of opening. I'm trying to study ...
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182 views
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112 views

Numerical modelling of a step function in time in a hydrodynamic system. (Runge Kutta fourth order)

So I'm trying to model a hydrodynamic system that introduces a sudden "jump" in the value of a function at a specific time. The system is solved with a Runge-Kutta fourth order method. I have a ...
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1answer
39 views

Does the length of a pipe influences the flow?

if I have a closed system of horizontal pipes, filled with water, where I want to create a flow at some rate by using a pump. Does the length of the system influences the flow ? (in real world not in ...
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1answer
96 views

Static pressure in ducts and its dependency on speed flow and density

I know that depending on the duct circuit (bends, complex geometries...etc), the static pressure will be defined. If we assume air is flowing in the circuit with varying speed and/or varying density. ...
2
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2answers
131 views

Cosmology: collisionless vs collisional fluids?

I try to understand the difference between collisionless and collisional fluids in cosmology. My first question is the following. In the context of FLRW cosmology, we suppose that the Universe can ...
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5answers
368 views

Is there a definite boundary between a powder and a fluid?

Given a powder of solid substance what will happen if we make the granules smaller and smaller mechanically? Will this eventually make a liquid or gas from the powder? Can there be gaseous substanse ...
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1answer
233 views

Why do some impact craters have an elevation in the center?

Why do some impact craters have an elevation in the center? What processes lead to its formation?
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105 views

Deceleration of spherical particle in fluid

If I know the initial velocity of a particle entering a fluid, how can I calculate its deceleration over time ? What parameters would I need to know ? Viscosity of the fluid, weight of the particle ......
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1answer
117 views

Is there a speed limit for objects falling in gases or liquids? [duplicate]

Let $o$ be a spherical object with mass $m$ and surface $s$. Let $g$ be the gravitational acceleration and $h$ the height. Let the gas where we drop $o$ in have density $d$ and pressure $p$ at ...
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2answers
869 views

Will going up with a larger diameter ensure a higher water pressure in the distribution pipes? [closed]

Have a look at the drawing below describing a sample situation: a water tank a 1'' diameter pipe bringing the water down, inside the ground, arriving near the house in the house, 2 x 0.5'' diameter ...
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1answer
110 views

what force pump is needed to power [closed]

Im studying design have not got a good grasp on maths, but understand the working principles of pressure and water! my problem hopefully has included all necessary info in the image. Please help. ...
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1answer
710 views

Exact solution to a 2D/3D Poiseuille flow in a channel

Hi everyone and thank you in advance for any help. I am struggling to find an analytical solution to either a 2D or 3D Poiseuille flow in a rectangular duct. All I can find is 1D example. Can someone ...
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1answer
179 views

Positions and corresponding terminology of “acoustics energy”?

From limited knowledge, decades ago, dating back to the nineteenth century: Ohm's law of specific acoustic energies was the first biological application of Fourier's theorem. Actually, it was ...
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1answer
66 views

can ice crystals be molded into a structural shape in space

I know that water exposed to vacuum space first boils and then turn into vapor (sublimates) . Is it possible re use this vapor say inside a pressurized membrane, to mold it into a solid ice structure, ...
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14 views

Saturn's Hexagon [duplicate]

I am currently trying to understand the formation or indeed the explanation as to why the hexagonal north polar vortex on Saturn is exactly that: Hexagonal. I understand that the most prominent ...
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1answer
147 views

Rain system movements and highways?

In my free time I sometimes enjoy watching the weather or radar and trying to predict how a rain system will move. Pretty often I notice that a small rain system or even a large one will congregate or ...
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1answer
193 views

Derivation of the energy-momentum tensor for an imperfect fluid

In chapter 7 of the "Physical Foundations of Cosmology" Mukhanov uses this energy-momentum tensor for an imperfect fluid: $T^\mu_\nu = (\rho + p)u^\mu u_\nu - p\delta^\mu_\nu - \eta(P^\mu_\gamma u^{;\...