# 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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### How to calculate the time it takes for an integral eddy to be reduced to the Kolmogorov microscale

I would like to calculate the time it takes for the largest eddies to be reduced to a specific size eddy (for example, the Kolmogorov length scale, but I would like a general equation if possible). I'...
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### Vortex line, tube, sheet, and filament

In my study of fluid dynamics I have across these terms quite often and I am so far unable to create a physical picture in my head. Suppose we have a 3D velocity field $u$, and its corresponding ...
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### Is turbulence more likely to form with the Euler equation as opposed to Navier-Stokes?

The Euler equation models perfectly inviscid fluids. Under this assumption, with $\nu = 0$, the Reynolds number should be infinite. I would guess that this implies the Euler equation is always ...
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### Does the resolution of a timeseries affect the estimate of the power-spectrum?

I have been trying to estimate the power spectrum of a timeseries using fourier transform. I noticed that by downsampling my timeseries I get a different spectrum as shown below Here you can see ...
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1 vote
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### What causes the formation of vortices in a separated flow?

Consider flow over a cylinder. At a high enough Reynold's Number, the strength of the adverse pressure gradient becomes too large for the boundary layer to be able to remain attached to the cylinder. ...
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### What is the eponym associated with the relationship between phase variance and expected magnitude?

I'm looking for the eponym (e.g., Stigler's law) associated with the following relationship: \begin{equation} \left|\langle e^{-i\phi} \rangle\right| = e^{-\langle\phi^2\rangle/2} \end{equation} which ...
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### Mass flow rate of fluid flowing over flat plate

When fluid flows over a flat plate, it forms boundary layer. Then velocity drops inside boundary layer. But how does mass conserved in this case? Initially total mass is having constant velocity ...
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### Are all turbulent flows chaotic?

I have often read that all turbulent flows are chaotic. I have come across a few explanations on web forums, but are there any authoritative references/textbooks that explicitly cover this question?
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### Can finite element analysis predict whether flow is turbulent?

Finite Element Analysis in Simulation Software to predict the Reynold's number are computed using the formula$=pVD/u$ or there is a finite element method for this? I was just wondering whether it ...
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### How to understand non-uniqueness of solutions of the Navier-Stokes Equations?

In the book of boundary layer theory: "The solutions of the Navier–Stokes equations do not have to be unique for given initial and boundary conditions. Primarily because of the nonlinearity of ...
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### How to tell if a system has a direct or reverse energy cascade?

We know, in 3D turbulence one observes a direct energy cascade, where the energy flows from the large scales to small scales (see wiki 1,1), usually attributed to vortex stretching. We also know that ...
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### Why fast trains make a white noise sound?

I have read that because turbulence has a fractal structure then all frequencies are excited equally and that makes the familiar whistling noise. Is this explanation correct?
1 vote
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### Why does blowing air through pursed lips make the air cooler than if we exhale through wide open mouth? [duplicate]

When we try to cool something through blowing on it, we purse our lips to exhale air through a narrow opening, which produces cooler air. However, if we open our mouths wide and exhale , then the air ...
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1 vote
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### Particle velocity field in turbulence

Consider solid particles in a turbulent flow. When is it appropriate to use a velocity field for the particles? To elaborate: In fluid mechanics, one uses the velocity field of the fluid as it is ...
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### How a shower head can affect water temperature? [closed]

This is a real-life case, that I simply don't understand :) A shower set is composed of a faucet $-$ that contains a mixer, a hose and a showerhead. The water comes from 2 pipes $-$ hot and cold. The ...
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