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

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About turbulence modeling

I have some questions about this paper: Lagrangian/Hamiltonian formalism for description of Navier-Stokes fluids. R. J. Becker. Phys. Rev. Lett. 58 no. 14 (1987), pp. 1419-1422. After reading ...
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132 views

Is drag force on an oscillating sphere an effective model for a swimmer?

I saw the latest video from Sixty Symbols Little Swimmers. At the end of the videos he says that we do not know how to calculate the movement of the little swimmers. He says(6:14-6:40 in video) that ...
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113 views

What is a superfluid in field theoretic terms?

I'm wondering how one precisely defines a superfluid in terms of the effective field theory description. In Nicolis's paper http://arxiv.org/abs/1108.2513 there seems to be an extremely simple ...
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What would be the optimal diameter of gold grains if you want to fill a pool with them and swim in it?

I was wondering, if I were to fill a pool with gold/gold dust, what would be the optimal diameter of the grains to minimalize the friction to a point at which you would be able to swim in it ((and if ...
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83 views

The Madelung Equations are Euler Equations for Quantum Mechanics. What is the Lagrangian description of Quantum Hydrodynamics?

The Madelung Equations of Quantum Mechanics suggest the Hydrodynamic Model of Quantum Mechanics (Quantum Mechanics is described as a fluid of universes in a multiverse, which, in the non-relativistic ...
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64 views

When beer tapping, why does only one of the beers foam up?

In the paper Physics of beer tapping the author go through an explanation of the phenomenon of beer tapping, i.e. the foaming up of beer in glass bottle after it has been hit at the top of the bottle ...
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79 views

Dispersion Relation for Convective Wave Equation

The convective wave equation governs the propagation of sound in the presence of mean flow: $$ \frac{D^2p'}{Dt^2}-\bar{c}^2\nabla^2p'=0 $$ or, expanded out: $$ \frac{\partial^2p'}{\partial t^2}+2\...
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36 views

How does air going through silica gel change its humidity

Assume that the properties(temperature,humidity,velocity and so on) of the incoming air flow stay constant. The air flow goes through a silica gel plate. Humidity of the air will decrease, but how to ...
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Difference between Eulerian and Lagrangian formulation of Fluid Dynamics

Difference between Eulerian and Lagrangian formulation of Fluid Dynamics. I am completely new to fluid mechanics. Until now definition $F = ma$ was sufficient for me to solve any rigid body problems ...
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46 views

Fluidics and surface tension

If a one cent coin is set carefully onto the surface of water horizontally (flat side parallel to the water surface). What are the relevant forces to determine if it would sink.
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47 views

How are boundary consitions implemented correctly in time dependent hydrodynamics?

I posted this question more than one year ago and got an answer recently. This answer looks good to me, but indicates that something is wrong in my original approach to the problem. Can someone tell ...
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63 views

Mass of star from Lane-Emden equation

Suppose we have equation of state $p=K\rho^{1+\frac{1}{n}},$ where $\gamma=1+\frac{1}{n}$ for some star. Then by standard calculations we obtain equation for enthalpy $h$: $$\Delta h+4\pi G\left(\frac{...
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38 views

Physical Meaning of Over- / Underdetermined Acoustic Eigenvalue Problem

I am performing an eigenmode study on a system of acoustic ducts. The system consists of two large cylindrical volumes connected by several smaller cylindrical volumes (modeling a combustion chamber ...
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38 views

Why would oscillation of a gas column inhibit rather than promote mixing?

Many years ago I helped to support an experiment conducted in Japan which investigated the effects of high frequency oscillation ventilation (HFOV) on the mixing and distribution of gas into the lungs....
3
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51 views

A question about droplets formation

This picture shows a fuel ejector of a diesel engine that propels ships. When the fuel line pressure exceeds 380 bars, the tension of the spring is overcomed and fuel is ejected into the combustion ...
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28 views

Could a hydrophobic surface increase a liquid's resistance to compression/displacement?

Imagine a quantity of an aqueous (yet slightly viscous) solution is resting on a hydrophobic surface with a contact angle around 100°. A downward force is then applied as a (repellant) surface is ...
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104 views

Dark matter “hair” flowing through the earth

Gary Prézeau of NASA's JPL has done some calculations of how dark matter might be focussed by the Earth's gravitational field (publication preprint), and the results show some remarkable hairy ...
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157 views

Why (and how) do foods stick to a pan?

We all (sooner or later) have noticed that foods relatively high in protein (especially those low in fat) are very prone to sticking to a pan, or in general to any non-specially-coated metal surface. ...
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95 views

What is the relationship between the angular speed and the diameter of the eye of a water vortex?

In a water vortex formed in a plastic bottle, what is the relationship between the angular speed of the water and the diameter of the hole in the cap? I would have expected that according to the ...
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157 views

seemingly impossible query

While on an expedition to a lake, it was noticed that the wind speeds gusted violently in seemingly periodic wakes and the proposed explanation was Von Karman vortex shedding off of nearby mountains ...
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89 views

Where else in physics does one encounter Reynolds averaging?

Reynolds-averaged Navier–Stokes equations (RANS) is one of the approaches to turbulence description. Physical quantities, like for example velocity $u_i$, are represented as a sum of a mean and a ...
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68 views

Modeling the formation of a stellar system and matter accretion

I am trying to figure out what do I need to know to properly simulate the creation of a solar system from a particle cloud with random distribution of hydrogen atoms. Being more of a programming ...
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203 views

Shock Rarefaction Interaction

I am interested to see/know if there exist analytical solutions for shock/rarefaction interaction. A rarefaction wave can catch up to a shock wave from behind. The shock will decay and the motion ...
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220 views

Conformal symmetry of Navier-Stokes?

This question is in reference to the paper arXiv:0810.1545 Can someone help understand this scaling argument and the proof(?) that there is a conformal symmetry in Navier-Stoke's equation? (..am I ...
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151 views

Difference between a Fixed Point and a Limit Point in implementations of the Renormalization Group (RNG) in Large Eddy Simulation (LES) model

In the introduction of this paper, it is explained that and how the application of a dynamic subrid scale model for turbulence into a large eddy simulation (LES) model corresponds to doing one ...
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103 views

Sound level of organ pipe driven by helium

The sound pressure level of an organ pipe is a function of the gas flow rate delivered to the pipe. Source Would the sound level of an organ pipe driven by helium be lower than that of a pipe driven ...
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152 views

How do I simulate a constant velocity flow in porous media

I am modelling gas combustion in porous media. Most contemporary models assume that the pressure drop from the porous media is small enough to disregard, but I want to include that in my investigation....
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264 views

Flow behind a plate causes pressure drop?

I've done an experiment where we direct an air jet from a fan onto a set of electronic scales. By measuring the velocity of the air jet at the exit of the fan nozzle, and applying the conservation of ...
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26 views

What are the dynamics of the “break the surface tension with a drop of soap” experiment?

There's a common experiment exemplified in the first few seconds of this video: https://www.youtube.com/watch?v=WsksFbFZeeU You put some food coloring in the center of a plate of milk, then put a ...
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38 views

Backing pressure for a turbo-molecular pump

It is known that turbo-molecular pumps are to be operated at already low levels of pressure. So the turbo is always backed by another pump (usually a scroll, rotary pump) that ensures this. One should ...
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25 views

Ratio of Stagnation to Normal Flow Properties in Incompressible Flows

I know in compressible flows the ratio of stagnation to normal flow variables is a function of the Mach number and usually the specific heat ratio. Does this ratio mean anything for incompressible ...
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57 views

Origin of spin and direction in the magnus effect

If you solve the Bernoulli equation: $$p=p_0-\rho_0{v^2 \over 2}$$ using a complex flow potential for a flow around a cylinder: $$W(z)=v_0 z + {v_0 R^2 \over z} - {\Gamma \over 2 \pi } \ln(z)$$ you ...
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38 views

Is there a general procedure for covariantizing equations?

I am currently attempting to derive covariant forms of equations whose domains are D=3 space. I am considering Lorentzian $(\mathbb{R}^4, \Omega, x, \nabla)$, where $\Omega \subset\mathbb{R}^4$ has a ...
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72 views

What causes angular deformation in an inviscid free vortex?

We can describe a two-dimensional (i.e. planar), inviscid, irrotational, free line vortex in cylindrical coordinates with the stream function $\psi = -K\ln{r}$, velocity potential $\phi= K\theta$, ...
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46 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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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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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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204 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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52 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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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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115 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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125 views

Why is the water in a cup not inclined (opposite the cup) when the plane takes a turn?

When a aircraft takes a turn: Why is the water in a cup not inclined (opposite the cup)?
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52 views

Are there any in depth superfluid mechanic analyses of spacetime?

Has there been much work done that treats particles as vortexes in a fluid, or dark matter as bubbles in this fluid (bending space in the same way massive particles (vortexes) are observed to do, but ...
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35 views

Fluid approximation for inflaton?

In cosmology there is a widely used fluid approximation which applies when the mean free path is very small compared to the scale of observation and then all the properties of stress energy tensor can ...
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247 views

Where can I find a table for NIST standards on temperature and pressure?

The Wikipedia article Standard conditions for temperature and pressure notes that IUPAC and NIST are two of the most common standards for temperature and pressure in use. Even if I could have gotten ...
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77 views

Are there resources for simulating and/or theoretically describing solitons?

Recently there are striking new ideas emerging on "lower level" dynamics with respect to quantum mechanics involving fluid mechanics principles, including hints of soliton-like aspects to particle ...
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71 views

What is the essential concept behind the difference in the fundamental solutions of the Stokes and Poisson equations?

The fundamental solutions, i.e., the solution with a point source, of the Poisson's equation and the Stokes equations in 3D are: $$\nabla^2 f=\delta(\boldsymbol x) \ \Longrightarrow\ G(\boldsymbol x,\...
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128 views

What does the net force do with this droplet in magnetic field?

Consider a spherical droplet with radious $R_d$ which is coated with an immiscible ferrofluid with volume equal to $2v_f$. While the droplet is in rest on a surface, if I approach two magnets in ...
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80 views

Definition of Irreducible Tensor Parts in an Exercise

I am addressing exercise 23.9 on http://www.pma.caltech.edu/Courses/ph136/yr2011/1023.1.K.pdf. The exercise says that a fluid flowing through spacetime $\vec u(\mathcal P)$ can have its gradient $\...
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How to make liquid marbles at home?

Some months ago I was reading a bunch of papers about the dynamics of liquid marbles. I was wondering if any of you have worked with them and know how to make them. I bought graphite and tried to ...