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Questions tagged [vortex]

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207 views

Can I determine if the flow laminar or turbulent from the vorticity?

I made a 3D model and i get a numbers for the vorticity but i can't know if this numbers can used to determine if the flow is laminar or turbulent. and if yes what is the critical value of the ...
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1answer
178 views

Vortex solution to Differential Equation

I am looking for a differential equation whose solutions are what I call "open" vortices. These vortices are not closed in themselves, but sort of "absorb" the surrounding "fluid" and also "emit" it. ...
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1answer
58 views

Superfluidity: separation of quantised vortices in a vortex tangle

It is often quoted (see https://doi.org/10.1016/j.piutam.2013.09.008) that the separation $\delta$ between quantised vortices in a vortex tangle in a superfluid is approximately $$\delta \approx L^{-...
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1answer
183 views

Smoke ring in space?

I understand that a smoke ring is an example of a vortex. I sort of grasp why a vortex stays coherent - the rotary motion of component molecules cause a pressure difference within the vortex. I do ...
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1answer
569 views

Are all Irrotational Flows Frictionless and Laminar?

A I understand, Irrotational flows are also inviscid (have zero viscosity). This would lead me to assume that these kind of (purely fictional) flows would be well ordered (Laminar) and be frictionless....
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1answer
2k views

Vorticity of a velocity field in cylindrical coordinates [closed]

I'm currently working on a obtaining the vorticity of my velocity field $u_r, u_\theta, u_x$. I know that this is equal to the curl of the velocity field $\nabla \times u$: $$\nabla \times u = \frac{...
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62 views

Cascade vs Inverse Cascade: Energy flow in 2D and 3D turbulence

We know that vortices tend to coalesce in 2D(inverse cascade) as opposed to 3D where they 'break down' into smaller vortices(cascade) ie. energy flows fro larger to smaller scales in 3D and opposite ...
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77 views

Why is the seperation of a tight pair of vortices a Topological Phase Transition?

I have been doing some research on Topology in Physics and so I came across this picture Source is this link. Now the way I understood Topology so far is that you can classify specific ...
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58 views

Thought experiment with conservation laws 1

So, imagine you have the following situation for two viscous fluids under a gravity field. Let's consider the walls and the fluid surface as our isolated system $\Omega$ (neither mass nor energy ...
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1answer
56 views

Conservation equations in a vortex

I have compared several models of vortex with experimental measurements considering only azimuthal velocity. So now, I would like to check if the conservation equations are satisfied at every point. ...
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2answers
65 views

Violation of Derrick's theorem for finite energy, time independent solutions?

How are vortices the finite energy time independent solutions for 2+1 dimensions abelian higgs model? Doesn't it violate derricks theorem that there are no finite energy time independent solutions in ...
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0answers
70 views

Why is the kinetic helicity of a fluid important?

In fluid dynamics, the kinetic helicity is a measure of the degree of knottedness and/or linkage of the vortex lines of the flow. It's a conserved and topological quantity. It has no effect on the ...
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44 views

How is this equation obtained?

I'm trying to code a script to solve aerodynamics problems with different numerical methods. I'm analyzing one method, in which I'm particularly stuck because I need to obtain a velocity equation, but ...
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4answers
1k views

Why does bathwater make a vortex in the plughole?

When I google for this I just get stuff about whether or not the Coriolis effect makes it go clockwise or anticlockwise, but I don't care which direction it turns in. I want to know why it turns at ...
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119 views

Why is it said that vorticity gets produced at a wall?

I am currently taking a fluids mechanics class and during the lecture the Prof. explained the following: when dealing with a 2D incompressible newtonian flow without external forces (gravity), ...
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156 views

Why are geodesic congruences irrotational?

In Sean Carroll's GR book "Spacetime and Geometry", in Appendix F on geodesic congruences, he defines a (timelike) geodesic congruence as the integral curves vector field so that: $$U_\mu U_\mu = -1$$...
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1answer
57 views

What makes air to spin?

The phenomenon is observed in tornadoes where the air spins with a great speed causing so much damage. Can there be any experiment that can be performed to make the air spin in clockwise or ...
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1answer
189 views

What causes fluid rotation in the Navier--Stokes equation?

It is known that rotation in the flow results from the viscous terms in the Navier-Stokes (N-S) equation. However, when deriving the N-S equation from the general principle of linear momentum in ...
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1answer
140 views

How can an axicon plus a convex lens produce an optical vortex?

The open access Nature paper Generation of “perfect” vortex of variable size and its effect in angular spectrum of the down-converted photons describes the use of an optical axicon (cone-shaped lens) ...
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2answers
67 views

Tornado vs sound speed

A tornado can be faster than sound, on Earth? Please explain as for a 6 years old (I am not the one interested in tornadoes).
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1answer
119 views

How many independent properties can a photon have?

Two recent papers about photon orbital angular momentum have set my head spinning as well. I'll try to define "property" as something you can change in one arm of a Mach-Zehnder interferometer, and "...
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1answer
345 views

Is there an explicit connection between rolling-shutter images of rotating propellers and interference patterns with optical vortices?

The rolling shutter effect is a neat fact of the geometry of modern CCD cameras and how they interact with objects that move faster than the camera can handle, and it's been beautifully explained by a ...
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1answer
497 views

Maximum speed of a toroidal vortex?

Consider a toroidal vortex, such as the iconic smoke ring or bubble rings that dolphins make at play. What is the maximum speed of such a ring? Since they are a fluid flow phenomenon it seems that ...
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0answers
88 views

Is there an Okubo-Weiss function for axisymmetric flows

I have recently learned about the Okubo-Weiss criterion in a ($x,y$) and a ($r,\theta$) coordinate system. Is it possible to recast this criterium in an ($z,r$) system, that is for axisymmetric ...
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1answer
111 views

How can we define $\Gamma$ (circulation) around a point vortex?

I'm having trouble understanding something in a book that I'm reading (Chorin & Marsden intro to fluid mechanics): Next we shall examine a model of incompressible, inviscid flow. We imagine the ...
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146 views

Do the Shallow Water Equations produce 2d vorticity/eddies? Why/Why not?

My understanding so far: given a small flow moving forward within a larger stationary body of water, the water ahead would pile up, creating hydrostatic pressure in all 2d directions (and thus ...
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0answers
24 views

Is the rotational velocity of a vortex consistent across its height?

I am trying to locate information about calculating the rotational velocity of a vortex. Is the velocity at the vertex maintained across the entire vertical height of the vortex? As the radius ...
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1answer
353 views

Why are superfluid vortex lattices stable?

Both (a) neutral superfluids that are externally rotated, and (b) type-II superconductors (i.e. charged superfluids) under applied magnetic fields between the critical fields $h_{c1}$ and $h_{c2}$, ...
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1answer
253 views

How do sound vortex cannons work

How does a sound vortex cannon amplify pressure waves? Does it work by compression, so that they are more focused, or in some other way?
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1answer
528 views

Biot Savart - Vortex line segment parallel to a plane

I am trying to understand what is shown in this book (Applied hydro and aeromechanics), page 187 https://books.google.com.au/books?id=Ds-bd0zAwIYC The velocity induced at a given point on a parallel ...
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1answer
94 views

Why do superfluid vortices form a lattice?

I often hear that in a superfluid, vortices get arranged in a lattice but I don't understand why and I've been hard pressed to find a discussion of it online. I'm aware that vortices should repel ...
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1answer
103 views

Why vortex lines should only end on themselves?

This is the Helmholtz theorem. Vortex lines never end on the fluid. What is the physical reason for this?
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1answer
77 views

Lifting line trailing vortex/vortex sheet inside flow field

With refference to the lifting line model, do we consider trailing votex or vortex sheet to be inside the flow field ? because the vortex core is rotational and we violate one of the flow field ...
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69 views

What is the singularity of a bathtub whirl?

I have read that at the center of a bathtub whirl the velocity should be infinite and that is a singularity. Could someone explain this and the mechanism that viscosity counteracts this infinite ...
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1answer
148 views

3-divergence of vorticity vector in GR

In Relativistic Cosmologies (Ellis, Maartens, MacCallum), the authors claim that (page 86, section 4.7) $$ \overline{\omega^i{}_{;i}} = \omega^i\dot{u}_i.\tag{A} $$ Here $u_i$ is a timelike vector ...
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1answer
55 views

Photonics, twist in laser beam, optical vortex

If I have a Gaussian beam and I use a spiral phase plate (SPP) to convert it into a vortex beam, I get a donut-shaped beam with zero intensity at the center. Imagine that I design an obstacle which ...
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0answers
558 views

Vorticity generation behind curved shock waves

The generation of a curved shock wave can take place in many applications. For instance, with high speed blunt bodies, the bow shock in front of the body will display a general curvature. Below is an ...
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3answers
556 views

Downwash created by horseshoe vortex at zero travelling speed?

This is a simple aerodynamics question about the horse shoe vortex. As it seems, the trailing edges on the side cause the downwash on the wing of the plane. However, since the circulation is constant, ...
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2answers
682 views

Necessary and sufficient condition for Bernoulli's theorem

For an ideal fluid, if the vorticity is $\vec{\omega}=\nabla \times \vec{v}$, then Euler's equations can be rewritten as: $$\rho \dot{v}_i = \rho \epsilon_{ijk} v_j \omega_k - \frac{1}{2} \rho \...
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0answers
105 views

Optical distortion caused by a vortex: “gravitational lensing” in a swimming pool?

Falaco solitons were accidentally discovered by professor R. M. Kiehn while he was visiting a friend's swimming pool. He describes them as [...] a pair of globally stabilized rotational ...
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0answers
135 views

Vorticity and the flow of a river [closed]

Q. a) If there's an obstacle at the bottom of a river why does one observe an indentation on the surface of the river at the position of the obstacle? Attempted solution: The water near the bottom of ...
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1answer
2k views

Vorticity and Shear - Irrotational and Rotational Vortex's

I have trouble understand how Vorticity occurs in a Rotational and not in a Irrotational vortex when I consider it in terms of shear forces. A Rotational vortex has a velocity profile where $v∝r$ ...
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1answer
801 views

Formal definition of 'pure straining flow' and 'pure rotational flow'?

In fluid mechanics the terms 'pure straining flow' and 'pure rotational flow' are often thrown around (see e.g. here). I have tried looking for a formal definition of these two but have not been able ...
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232 views

order of BKT phase transition

What is the order of the BKT phase transition (first or second), that is the phase transition in 2d in which thermal vortices destroy any order in the system. How is this connected to the "universal ...
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1answer
464 views

Relationship between laminar flow, vorticity and vortex formation in a fluid?

Is it true that for a fluid in laminar motion the vorticity is zero? $$\mathrm{laminar} \implies \, \mathrm{rot} \,\vec{v}=0$$ And is it true that if the vorticity is zero (as in the situation above)...
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1answer
47 views

Vortice flow comparison

Suppose the flow of a 1 square meter circle surface vortex. If instead of 1 vortex I stick say 100 smaller vortices in the same area. Will the total flow of 100 parallel vortices be larger that the ...
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0answers
201 views

How to define a vortex core without first defining a vortex?

A common definition of a vortex is that proposed by Robinson 1991 : A vortex exists when instantaneous streamlines mapped onto a plane normal to the vortex core exhibits a roughly circular or ...
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177 views

Physics behind a blue “firenado”

In the NYTimes video Harnessing the Firenado, a rotating yellow sooty flame is suddenly transformed into a clean blue rotating flame. What is the physics behind this transformation? What is it about ...
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2answers
2k views

Why is the eye of a cyclone a forced vortex?

As far as I understand, a forced vortex has a velocity profile $u \propto r$ ($r$ is radial distance from centre of vortex), concluding at some outer boundary $r=R$ to avoid fluid particles ...
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1answer
202 views

If there is a super massive black hole at the center of our galaxy then why is the center of our galaxy so bright? [duplicate]

Below is our galaxy, if there is a such a massive black hole at the center then wouldn't it suck in any light traveling above it, or is the amount of light put out by stars near the center so great ...