# Questions tagged [turbulence]

A regime of nonlinear viscous flow characterized by random, rotational motion with a wide range of length scales. Its study is critical to many fields, such as aerospace, atmospheric science, chemical engineering, and astrophysics.

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### In turbulent flow, where is the friction of the pipe exactly? Is it between the laminar layer and the pipe walls or the turbulent layer and laminar?

In turbulent flow as we get closer to the pipe walls we encounter an overlap layer and then a layer of laminar flow. Also at the walls of a pipe, in turbulent flow, the laminar shear stress dominates. ...
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### Favre Averaged Navier-Stokes equations

Consider the Navier-Stokes (NS) equation \frac{\partial (\rho u_i)}{\partial t} + \frac{\partial (\rho u_i u_j)}{\partial x_j} = - \frac{\partial p}{\partial x_i} + \frac{\partial}...
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### Does Navier-Stokes equations get correct result for complex turbulent flow without turbulence model?

Does Navier equations (1822 formulation) get correct result for complex turbulent flow without turbulence model? Is this 1822 formulation?
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### Transition from laminar to turbulent and vice versa

Let's imagine a viscous fluid flowing horizontally through a cylinder with inner diameter $d$. The Reynolds number for that setting is described as: $$Re=\frac{u\cdot d}{\nu}.$$ The fluid is first ...
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### Prediction of the drag coefficient at high Reynolds number

The picture reflects the classical variation of the drag coefficient of the sphere concerning Reynolds number. For the Reynolds number chosen, we know that the drag coefficient is the summation of ...
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### Turbulence in flow of spacetime

Why is there no turbulence in the flow of spacetime around black holes? How does this flow differ from typical physical flows described by the Navier-Stokes equations with friction, or even the ...
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### References for multifractal complex measures?

I am learning about multifractal formalism recently. It seems nearly all the work is done for real-valued measures. Question: I am wondering whether there is study (or even definition!) for ...
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### Why cornering wind tunnel rotate?

Why cornering wind tunnel rotate, why is not just curved? A curved wind tunnel has a radial pressure gradient, but this pressure gradient doesn't exist in a real turn, so how do you get zero pressure ...
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### Does (and how) a shark fin on car top (or fan blade) reduce drag?

I've heard this kind of shark fin on the roof reduces drag by breaking the wave that forms behind, where the roof bends into rear window. image source The story goes that it's similar to these fins ...
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### Lift generated by airfoil and why does a flow with a positive angle of attack around a flat plate curve upwards instead of downwards?

I've recently been reading about what really causes lift on an airfoil and the article linked mentions that even a symmetric airfoil or even a flat plate generates lift as long as the angle of attack ...
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### Can protrusions on the smooth surface of a floating (or flying) body not slow it down, but accelerate it?

These protrusions are sure to create turbulent vortices. But what if these additional vortices can somehow lead to acceleration? Additional clarification It is clear that moving protrusions such as ...
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### Why are cylinders more aerodynamic than spheres?

Why are cylinders more aerodynamic than spheres? Say you have a cylinder falling vertical that has rounded ends. Now remove the cylinder part. Now you’re left with a sphere but without the skin ...
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### If lidar is used underwater, would passing through a turbulent surface into a pocket of air (e.g. a "moon pool") distort the resultant image at all?

I have zero experience with lidar systems, but I have been under clear water and looked up at the interior/ceiling of an indoor pool, and even the slightest turbulence at the surface distorts what I ...
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### Turbulence in Spacetime [duplicate]

Is it possible for the phenomenon of turbulence – eddys and vortices on many scales – to occur in spacetime in the context of General Relativity? For example near a Kerr black hole. If not, what is ...
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### Can angular momentum be transported between scales in turbulent flows?

Consider a turbulent rotating flow. You are interested in its average features so you use the Reynolds-averaged Navier-Stokes equation. Now, conservation of angular momentum implies the viscous ...
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### What is a structure function in turbulence?

I'm new to turbulence, so I don't understand what a structure function represents. I also wanna know its physics meaning in turbulent small scale structure.
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### Fourier transform of velocities of individual particles vs coarse-grained velocities

In fluid dynamics, we are interested in $E(k,t)$ the energy in mode $k$. From the velocity field $v(x, t)$, $E(k, t)$ can be computed by simply taking the Fourier transform of $v(x, t)$, squaring, etc....
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### What is the relevant phenomenon behind Undulatus/Radiatus cloud formations?

I am seeing many people claiming that cumulus clouds that sometimes form periodic wavy patterns (see images for "altocumulus undulatus" or "Radiatus" for instance) have no ...
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### The proportionality of a Drag force and speed

At low speeds, Drag force is proportional to speed due to Stokes law. At higher speeds, Drag is proportional to the square of speed. While modelling the speed of a water rocket, I realised that when ...
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### Can an ideal fluid undergoes a turbulent flow?

I have read before that the existence of viscosity is the main reason for the appearance of vortex. However, by definition, an ideal fluid has $\eta=0$. So, can an ideal fluid undergo a turbulent ...
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### Magnetic Field of Earth and Turbulence of plasma

We generally know that plasma turbulence creates magnetic field (here, I have assumed that it happens through the dynamo effect). it is also affected by magnetic fields. Is it possible that plasma ...
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### What scaling law does the two-dimensional isotropic turbulent energy spectrum satisfy as k tends to 0?

What scaling law does the two-dimensional isotropic turbulent energy spectrum satisfy as k tends to 0? Can you recommend some references? Thanks a lot!
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### Identity with projector tensor

I'm reading Yakhot and Orszag article on Renormalization Group Analysis of Turbulence, and I got stuck in a step, which I don't know if it is an identity or if it has some approximation involved. ...
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### How to estimate the Kolmogorov scale of the plasma in solar corona?

I would like to estimate the order of Kolmogorov scale $$l_k = \left( \frac{\nu^3}{\epsilon_d}\right)^{1/4}$$ of the plasma in solar corona, so I need to determine the viscosity $\nu$ and ...
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### Can Kolmogorov spectrum be used to describe the plasma fluctuations in the atmosphere of neutron star?

I am wondering that whether Kolmogorov spectrum, which describes the energy distribution in turbulence be used to describe the plasma fluctuation in the atmosphere of neutron star. As I know, ...
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### Factor in Gaussian filter

Why do Gaussian filter kernels commonly used in turbulence studies often have a factor of 6? $$G_{\ell}(|x|) = \left( \frac{6}{\pi \ell^2} \right)^{n/2} \exp \left( -\frac{6}{\ell^2} |x|^2 \right)$$ ...
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### Why don't they use golf ball dimples on cars? [duplicate]

Just watched an episode of mythbusters where they proved that a car got better fuel economy with golf ball dimples. So why don't they use that on cars?
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### Questions regarding the derivation procedure of the Karman-Howarth-Monin relation

I was reading the book "Turbulence" written by Uriel Frisch (1995) and got stuck in following the proof of the Karman-Howarth-Monin relation. Although there is already a thread about it, I ...
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### Value of the velocity at the largest correlation length in a turbulent medium

If a turbulent system is observed to follow a turbulent energy spectrum of the form $E(k)\propto k^{-p}$ for the range $k_{min}<k<k_{max}$, I was wondering if there is a way to have an order of ...
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### At What Scales Turbulence Matters?

So from what I understand(like from this site: https://www.britannica.com/science/transport-phenomenon) is that turbulence is when the flow is almost unpredictable at different parts but on average ...
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### Some questions in book of Frisch&Kolmogorov at Chapter 6

i'm not native speak, what does the above sentence meaning? —— whether the sentence “which are small compared to the integral scale” refers to increments $\ell$ only or refers to increments $\ell$ &...
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### How to understand the Fourier transform of a stationary random function?

A stationary random function like $v(t;w)$ is not periodic and not squared integrable, why we can do a Fourier transform to it, which is a very common process to analyze turbulence. How will a ...
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### Is it possible to convert separated flow back to attached?

Sometimes you cannot easily create ideal single streamlined shape... Would it be possible to attach separated flow again somehow? The point is - you have some base setup (average cyclist) and want to ...
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### Turbulence, Euler equations and equipartition of energy

Recently the user CBBAM asked about the inviscid limit in turbulence and the relation between Navier-Stokes equations and Euler equations when $\nu \to 0$. There I pointed out that Onsager proposed ...
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### What is the correct direction of turbulence energy cascade?

I have learned from a fluid mechanics textbook [1] that the turbulence energy is cascaded from the largest eddy to the smallest eddy and is then dissipated by the molecular viscous effect. But ...
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### Can someone give a picture to visualize and elucidate the celebrated rhyme of Richardson about turbulence? [closed]

Richardson's celebrated rhyme is below: Big whorls have little whorls, which feed on their velocity, and little whorls have lesser whorls, and so on to viscosity. (Lewis F. Richardson, 1920) I read ...
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