Tagged Questions
5
votes
0answers
65 views
Why is there no UV catastrophe (divergence) in turbulence?
I have just read that as the Reynolds number is increased, the separation of macroscopic and microscopic scales increases and that this also means that there is no UV catastrophy (or equivalently UV ...
3
votes
1answer
60 views
What does the Reynolds Number of a flow represent physically?
What does the Reynolds Number of a flow represent physically?
I am having trouble understanding the meaning and the utility of the Reynolds number for a certain flow, could someone please tell me how ...
1
vote
0answers
22 views
What is the relationship between complex time singularities and UV fixed points?
In this paper it is described how the turbulent kinetic energy spectrum and the flatness (a measure for intermittency) are governed by the position of the (dominant) singularities of the solutions of ...
1
vote
0answers
94 views
2-D Turbulence - how does it look like?
Consider parallel flow in the X direction over a 2D semi infinite flat plate. If turbulence is 2-D, in which axes should we expect the vortices to form.
Also, are there any experimental/visualization ...
1
vote
0answers
46 views
Physical interpretation of an intermittency definition
A random function $v(t)$ is said to be intermittent at small scales of its "Flatness" $F$, given as
$$
F(\Omega) = \frac{\langle (v_{\Omega}^{>}(t))^4\rangle}{\langle ...
5
votes
1answer
211 views
What is the mystery of turbulence?
One of the great unsolved problems in physics is turbulence but I'm not too clear what the mystery is. Does it mean that the Navier-Stokes equations don't have any turbulent phenomena even if we solve ...
1
vote
1answer
126 views
how to determine if a vortex is laminar or turbulent
In a cylindrical chamber with a high diameter-to-height ratio; a fluid is tangentially injected. there is an axial exit to the cylinder.
how do I determine if the vortex so formed is laminar or ...
2
votes
0answers
78 views
Difference between a Fixed Point and a Limit Point in implementations of the Renormalization Group (RNG) in Large Eddy Simulation (LES) model
In the introduction of this paper, it is explained that and how the application of a dynamic subrid scale model for turbulence into a large eddy simulation (LES) model corresponds to doing one ...
4
votes
0answers
103 views
Can a divider “laminarize” turbulent flow and thus reduce friction?
Looking at the Moody chart I think to myself, the friction factor doesn't decrease much at all with Reynolds number after a certain point. I wonder if laminar flow is more efficient in a sense, and ...
3
votes
1answer
166 views
How to estimate the Kolmogorov length scale
My understanding of Kolmogorov scales doesn't really go beyond this poem:
Big whirls have little whirls that feed on their velocity, and little whirls have lesser whirls and so on to viscosity. ...
7
votes
2answers
387 views
What is enstrophy?
In turbulence, the enstrophy of a flow in a domain $\mathcal{D} \subset \mathbb{R}^{D}$
$$
\mathcal{E} = \int_{\mathcal{D}} |\vec{\nabla} \times \, \vec{v}|^2 d^{D}x
$$
appears sometimes, it's cool ...
2
votes
1answer
106 views
Is it wrong to associate non-isotropic flow high with Reynolds-Number and is there a better metric?
IT is often stated the flow with high Re is not isotropic, meaning there is no uniform or dominant direction of the flow. But this seems wrong to me - -while there's certainly cases where no dominant ...
12
votes
2answers
121 views
Cascade in relativistic turbulence
The Kolmogorov theory of turbulence indicates an energy cascade in turbulence. Is there a corresponding version of relativistic fluid?
6
votes
1answer
295 views
About Turbulence modeling
There is a paper titled "Lagrangian/Hamiltonian formalism for description of Navier-Stokes fluids" in PRL. After reading the paper, the question arises how far can we investigate turbulence with this ...
0
votes
0answers
71 views
Energies decay in 3D homogeneous rotating turbulence
In three-dimensional rotating homogeneous turbulence governed by the hyper-viscous Navier-Stokes equation with an additional Coriolis force in a three-periodic setup:
\begin{equation}
...
1
vote
1answer
98 views
Does turbulence violate Galilean relativity?
Fluid flows become turbulent beyond a certain velocity. The velocity is almost always with respect to a fixed boundary. However, an observer in a frame of reference travelling with the fluid will also ...
2
votes
2answers
279 views
Vortex street and Reynolds number
Its been stated in Wikipedia regarding Reynolds number(Re) that "laminar flow occurs when Re<2300 and turbulent flow occurs when Re>4000. In another wiki file related to Kármán vortex street it has ...
3
votes
1answer
80 views
Critical bathymetric profile to maximize surge and minimize breaking?
Reading about storm surge, I found it fascinating that the gradual slope of the Gulf Coast of Florida resulted in a much higher storm surge but much lower energy release in breaking waves.
Is there ...
5
votes
1answer
354 views
Turbulence parameterization from gravity - fluid dynamics correspondence
I`m looking for a nice introductary reference that explains how the turbulence coefficient or any kind of turbulence parameterization (in view of applications to atmospheric turbulence for example) ...
8
votes
3answers
347 views
Occurrence of turbulences in Fluid Dynamics from the equations of motion?
How can it be shown that turbulences occur in Fluid Dynamics?
I think poeple imply that they develope because of the $\text{rot}$ terms in the equations of motion, i.e. the Navier-Stokes equations, ...
3
votes
1answer
125 views
Effect of rotation on turbulence threshold for Reynolds number?
If the significance of the Reynolds number is:
Then what is the effect of angular momentum on the transition from laminar to turbulent as in a convective vortex? Waterspouts, in particular, seem ...
0
votes
0answers
348 views
Reynolds Number and relation to Moody Diagram for a Small Pipe
I am having the following problem on a lab write up:
Calculate the approximate distance downstream of the inlet that
corresponds to the hydrodynamic entry length for Reynolds numbers of
3,000 ...
17
votes
3answers
791 views
Have we figured out how to analyze turbulent fluids?
I was surprised to read that we don't know how to analyze turbulent fluids. On page 3-9 of The Feynman Lectures on Physics (Volume One), Feynman writes:
Finally, there is a physical problem that ...
9
votes
3answers
150 views
What does the quantification of causes and effect look like, for clouds in offshore wind turbine wakes?
At Horns Rev windfarm off the coast of Denmark, sometimes in winter, clouds appears in the wake of the turbines. I've only seen photos of the phenomenon when the wind direction is exactly aligned with ...
8
votes
1answer
353 views
Physical Explanation for “Kolmogorov -5/3 spectrum” in Fluid Mechanics
According to Kolmogorov, the energy spectrum function of a turbulent fluid is given as,
$E(k)=C\epsilon^{\frac{2}{3}}k^{\frac{-5}{3}}$
where $\epsilon$ is the energy flux and $k=\frac{2\pi}{r}$ ...
3
votes
1answer
303 views
How to derive the Karman-Howarth-Monin relation for anisotropic turbulence?
I find the derivation of the Karman-Howarth-Monin relation in the book Turbulence from Frisch (1995) a bit to short. Can someone point me to a more detailed derivation of that relation, if possible in ...
0
votes
1answer
191 views
What is it that makes this structure cause turbulence?
I'm trying to design a quasi-simple vertical axis wind turbine, and a coworker came up with this design to focus the wind as it reaches the turbine in a wind tunnel. He says that there's going to be ...
7
votes
7answers
529 views
Does the wind gust over the ocean?
It is easy to observe that on a windy day, the wind does not blow for several hours at constant speed, then gradually subside. Instead, on a time scale of seconds or tens of seconds, there are ...
