# 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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### Are any advanced Reynolds-averaged fluid models used in astrophysics?

Reynolds-averaged Navier-Stokes equations allow to split the description of a turbulent fluid into an averaged (typically laminar) flow on some length and/or time-scale and separate equations for the ...
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### What is the “sweeping velocity” of a turbulent flow?

Background: While reading Rubenstein and Zhou 1997 I encountered an unfamiliar term, "sweeping velocity". To quote the authors (pg. 3): ...the sweeping hypothesis makes the decorrelation depend ...
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### Spectral analysis of turbulent flow

I have the "energy spectral density" curve for a specific location in a turbulent flow. My curve is based on turbulence frequency (w) rather than wavenumber (k). The mean kinetic energy can be ...
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### Will cigarette smoke show an onset of turbulence in vacuum?

In this video one can see how cigarette smoke changes from laminar to turbulent flow. The conditions, though, are far from ideal (by which I mean that the air in which the smoke flows has no common ...
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### Would $\nu/k$ be a meaningful timescale in turbulence?

If we consider kinematic viscosity $\nu \, [\text{m}^2/\text{s}]$ and turbulence kinetic energy $k \, [\text{m}^2/\text{s}^2]$, we can form a timescale $$\tau = \frac{\nu}{k}.$$ Is it a ...
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### Simulating atmospheric turbulence

This problem comes from simulation of atmospheric turbulence. It starts with the following transfer function in the frequency domain: \begin{equation} G_v(s)=\sigma k_1 \frac{1 + k_2 s}{\left(1+k_3 s\...
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### Acoustic power spectrum of a natural turbulent flow

For a long time I've been curious about predicting the acoustic power spectrum of river sound from hydrodynamic measurements. What got me started thinking about this topic was repeatedly observing ...
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### Model for sound generated by air flowing through pipe

I'm trying to write a program simulating the sound of an petrol car engine, just for fun. As a part of this, I'm trying to model the sound of air escaping the combustion chamber through an open ...
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### Turbulence Model on Unsteady Navier Stokes

I am asking you if the Unsteady (Time-Dependant) Navier-Stokes Equation is able to predict accurately the Flow Turbulence? I know that the RANS (with different Turbulence Models like Spalart–Allmaras, ...
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### Is friction higher or lower in laminar vs turbulent boundary layer?

Is friction drag more or less in laminar boundary layer vs turbulent boundary layer? It is written in this page of wikipedia: The laminar boundary is a very smooth flow, while the turbulent ...
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### Validity of the Navier Stokes equations for turbulent flows

The derivation of the Navier-Stokes equation presupposes that the pressure, $p$, and velocity, $u_i$, are infinitely differentiable, so that the forces in each face of the fluid element can be ...
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### Stratification vs Compressibility

This is a rather peculiar question to ask because as far as I know these two have sort of independent definitions, i.e. stratification is not necessarily associated with fluid motion on the other hand ...
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### What is the physical interpretation of Rayleigh's inflection point theorem?

Let $\boldsymbol{u} = U(z)\,\mathbf{e}_x$ be the velocity profile of an inviscid parallel flow. Rayleigh's inflection point theorem states that this flow may be linearly unstable to perturbations only ...
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### Stochastic process vs high dimensional chaos in models

I'm trying to figure out what are the theoretical and practical, implications and limitations, when a high-dimensional chaotic process is modeled as a random process. I understand how low-dimensional ...
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### About the aerodynamic force on a rotating maple leaf seed

Every matured (ready to fall), wing-shaped seed of the maple leaf tree ends up in a rotating motion, no matter what it's initial position is (the seed follows the path of least action, or in more ...
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### Onset of turbulence

Does every fluid undergo a transition in the presence of disturbances? Even if we could isolate the disturbances entering the boundary will the fluid still undergo transition and become turbulent ...
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### Turbulence: a state, a property, a structure?

This is a pure terminology question. The term "turbulence" ("turbulent" etc.) appears in many phrases from an ordinary technical description to apparent parables. In my limited knowledge, turbulence ...
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### Turbulent flow and Separated flow

My knowledge in aerodynamics is very limited as I am doing just an introduction to the subject, and so I may not understand very complex explanations. I know that at some point laminar flow becomes ...
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### Does the turbulence of a fluid flowing through a pipe decrease with the distance from the entrance?

Consider a constant-diameter L-shaped pipe with an entrance and an exit. If water is being pumped into the pipe at a constant rate, the flow rate of the water at the exit must equal that at the ...
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### Why does laminar flow turn turbulent(*) in external fluid flow and why doesn't a fully developed laminar flow turn turbulent in flow through pipes?

(*:with increase in distance from the leading edge.) I would appreciate if you give detailed explanation for the first question and then apply the same logic to answer the second.