The turbulence tag has no wiki summary.
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In turbulence theory, what happens if i take space average of fluctuating part?
According to Reynolds decomposition, velocity field is split into two time average and fluctuating parts:
$$u_{({\bf x},t)}=\overline u_{(\bf x)}+u'_{({\bf x},t)}$$
we know that time average of ...
1
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0answers
34 views
Is this the reason solids suspended in turbulent fluids don't settle?
While I know (and can observe) that solids don't settle easily in a turbulent flow, I struggle with understanding why exactly this is the case. Here' my problem:
Conceptually, turbulence means high ...
0
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1answer
44 views
Navier-Stokes - Complete set under turbulent eddy viscosity hypothesis
I'm looking for the complete set (x,y,z component) of the Navier-Stoke equations under the Eddy Viscosity hypothesis to model turbulent fluid flow.
I found the following, but I have a really hard ...
6
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1answer
89 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
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1answer
84 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
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0answers
23 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 ...
10
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1answer
83 views
Can Increasing the Turbulence Inside a Pipeline Economically Increase Flow?
"The velocity gradient in turbulent flows is steeper close to the wall and less steep in the center of the pipe than it is for laminar flows (Blatt p.97)."
Does this mean that some degree of ...
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0answers
98 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 ...
0
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1answer
53 views
Equivalence of turbulence in solid materials
The governing equations for a fluid and a solid are effectively the same and many times analysis can be done for a solid using the Navier-Stokes equations with the equation of state and/or the stress ...
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0answers
53 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
$$
F(\Omega) = \frac{\langle (v_{\Omega}^{>}(t))^4\rangle}{\langle ...
7
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2answers
297 views
What is the mystery of turbulence?
One of the great unsolved problems in physics is turbulence but I'm not too clear what the mystery is. Does it mean that the Navier-Stokes equations don't have any turbulent phenomena even if we solve ...
1
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1answer
145 views
how to determine if a vortex is laminar or turbulent
In a cylindrical chamber with a high diameter-to-height ratio; a fluid is tangentially injected. there is an axial exit to the cylinder.
how do I determine if the vortex so formed is laminar or ...
2
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0answers
82 views
Difference between a Fixed Point and a Limit Point in implementations of the Renormalization Group (RNG) in Large Eddy Simulation (LES) model
In the introduction of this paper, it is explained that and how the application of a dynamic subrid scale model for turbulence into a large eddy simulation (LES) model corresponds to doing one ...
4
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0answers
112 views
Can a divider “laminarize” turbulent flow and thus reduce friction?
Looking at the Moody chart I think to myself, the friction factor doesn't decrease much at all with Reynolds number after a certain point. I wonder if laminar flow is more efficient in a sense, and ...
3
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1answer
222 views
How to estimate the Kolmogorov length scale
My understanding of Kolmogorov scales doesn't really go beyond this poem:
Big whirls have little whirls that feed on their velocity, and little whirls have lesser whirls and so on to viscosity. ...
7
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2answers
487 views
What is enstrophy?
In turbulence, the enstrophy of a flow in a domain $\mathcal{D} \subset \mathbb{R}^{D}$
$$
\mathcal{E} = \int_{\mathcal{D}} |\vec{\nabla} \times \, \vec{v}|^2 d^{D}x
$$
appears sometimes, it's cool ...
0
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2answers
45 views
Why is the turbulent energy cascade described as function of a wavenumber?
In all the literature I've seen the turbulent energy spectrum described as $E(k)$ instead of $E(L)$, i.e. as a function of a wave number not eddy size. The connection via $k=2\pi/\lambda$ is clear, ...
2
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1answer
113 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 ...
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2answers
128 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
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1answer
303 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 ...
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0answers
75 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}
...
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0answers
59 views
Need advice on bluff-body aerodynamic research
I am from civil engineering, I am doing simulation and analysis (CFD and other statistical method) on flow around bluff bodies as in a wind tunnel. Different from in aerospace aerodynamics, our ...
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1answer
102 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
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2answers
298 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
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1answer
82 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
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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) ...
3
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0answers
82 views
Turbulence forming between the coaches of rail
is there any specific reason why rail coaches are connected by a rubber sheet; not of any other material ?
I watched a documentary on trains (Discovery Channel) which said it connecting coaches by ...
5
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0answers
171 views
Are there known turbulent nonlinear equations where the cascade is a thermal gradient?
In a recent answer (here: The equipartition theorem in momentum space ), I suggested that if you have an appropriate first order equation (in the answer I used a second order equation, but it is more ...
6
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1answer
445 views
The equipartition theorem in momentum space
Motivated by the answers to this question on turbulence, I'm interested in an explanation and/or derivation/reference of the equipartition theorem in momentum space. To formulate it as a question:
...
8
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3answers
354 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
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1answer
134 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
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0answers
360 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 ...
18
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4answers
943 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 ...
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3answers
153 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
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1answer
363 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
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1answer
322 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
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1answer
195 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 ...
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7answers
542 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 ...
9
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1answer
531 views
Fractal nature of turbulence
Someone described to me the difficulty of numerically simulating turbulence as that as you look at smaller length scales you see more structure like you do in a fractal. Searching on google for ...
9
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3answers
454 views
How to calculate the upper limit on the number of days weather can be forecast reliably?
To put it bluntly, weather is described by the Navier-Stokes equation, which in turn exhibits turbulence, so eventually predictions will become unreliable.
I am interested in a derivation of the ...
