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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89 views

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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323 views

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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129 views

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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311 views

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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45 views

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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203 views

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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194 views

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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2answers
678 views

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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474 views

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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108 views

Decay of correlations in turbulent flows

Rich literature exists that discusses the decay of correlations in the velocities between two points in space and time: $ R(r,\tau) = \mathbb{E}\left[ v({\bf x},t) v({\bf x} + r {\bf e}, t + \tau)\...
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Why does rainwater form moving waves on the ground? Is there a name for this effect? [duplicate]

A while ago it was raining and I noticed that, on sloped pavement, water was flowing in very regular consistent periodic waves, as you see below. However, I realized I had no idea why this should be ...
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Kolmogorov scaling what holds where? [closed]

I have asked a few questions on Kolmogorov scaling before but am still struggling to understand it due to the many different notations and conventions used - as well as a lack of any rigorous resource ...
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Is cigarette smoke an example of turbulent flow?

Everywhere in internet and books that introduce to fluid dynamics mention cigarette smoke as a classical example of turbulent flow. But the velocity, in other words the Reynolds number, is small. How ...
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105 views

How shear free jets become turbulent?

Turbulence always need a surface in order to be created, an aeroplane wing or the walls of a pipe per example. How free jets become turbulent when they are just surrounded by air?
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A taylor expansion for fluids

A while back I asked the question In fluid dynamics does $u_x-v_y$ have a name?. The reason for my question was due to it's presence in the following Taylor expansion about the orgin (see (1)): $$\...
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719 views

Why are ceiling fans so much quieter than others?

I used to live in a house that had ceiling fans, which were great for the summer and so wonderfully silent when running. Now however I've moved to a house that has no ceiling fans so I've bought a ...
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467 views

Kolmogorov scaling the meaning of the inertial subrange?

I am reading Landau and Lifshitz (Fluid Mechanics) and they say something that contradicts my current understanding of the inertial subrange. I thought (and have read in numerous sources) that the ...
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255 views

Fire tornado experiment: turbulent vs laminar flow of air?

Consider this experiment: https://www.youtube.com/watch?v=1BxQd6AGYiI&app=desktop A pot of highly-flammable liquid burns with a small flame if placed on an extensive flat surface (observation A)....
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320 views

Kolmogorov scale - dissipation?

The rate at which energy moves down a turbulent cascade is given by: $$ \newcommand{\p}[2]{\frac{\partial #1}{\partial #2}} \newcommand{\f}[2]{\frac{ #1}{ #2}} \newcommand{\l}[0]{\left(} \newcommand{\...
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264 views

Extending the Bernoulli Equation to Rotation

The standard Bernoulli Equation has three terms on each side, a kinetic energy term, a potential energy term and a pressure term. I've never seen an extension of this to also include a rotational ...
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Ways to compute the turbulent velocity kinetic energy spectrum

The implicit definition of the kinetic energy spectrum $\hat{E}_k$ of the turbulent flow is simply: $$ E = \int \hat{E}(k) \mathrm{d}k $$ I have found the definition using Fourier transform of a two-...
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177 views

Turbulence in Statistical Mechanics approach

Is it feasible to describe Turbulence (at continuum scale) using Statistical mechanics approach? For example, Is it reasonable to model a turbulent round jet at an instant time in space as a $N,V,T$ ...
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Optical distortion caused by a vortex: “gravitational lensing” in a swimming pool?

Falaco solitons were accidentally discovered by professor R. M. Kiehn while he was visiting a friend's swimming pool. He describes them as [...] a pair of globally stabilized rotational ...
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How do I find the impact pressure of cavitation due to imploding super critical fluid bubble?

I have solved the Rayleigh-Plesset equation for a time varying bubble of a super critical fluid. I am trying to find if the impact pressure caused by SCF bubbles is lesser as compared to that caused ...
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Time scale turbulence flow -distance between two particles

I want to estimate the time interval, $\tau$, during which the original distance $L$ between two fluid particles become much larger. I assume that the motion takes place in the inertial interval. I ...
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248 views

How does the wing area affect the form drag and induced drag? And also lift?

I did an experiment of 8 different square wing areas. And found out that as the wing area increases, the wing vibrates more. (I made the wings out of hard paper) Does this mean that this is due to ...
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About the definition of boundary layer

I've a question regarding the definition of the velocity boundary layer. The boundary layer is defined (correct if I'm wrong) as the region close to the body where viscous effects are important and ...
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791 views

Blender physics: Size of ice cubes affects crushing of nuts

By using a blender to prepare my breakfast shake (containing ice and nuts amongst others, see ingredients below), I made the following observations. Case 1: Using large ice cubes will result in a ...
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2answers
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Kolmogorov scale why $d\sim \left( \frac{\nu^3}{\epsilon} \right)^{1/4}$ and not $d\propto \left( \frac{\nu^3}{\varepsilon} \right)^{1/4}$?

I am looking at the Kolmogorov scale and in numerous sources (e.g. this one). I have seen the following: $$d\sim \left( \frac{\nu^3}{\epsilon} \right)^{1/4}$$ for the Kolmogorov scale. I can see why ...
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Links between laminar-turbulent and steady-unsteady flows

I report some definitions of flow characteristics as given on Cengel Cimbala. Laminar or turbulent Laminar flow: A stable well-ordered state of fluid flow in which all pairs of adjacent fluid ...
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51 views

Is there a basis for naming these empirical fluid model coefficients in terms of flow regime?

Given any flow restrictive device (e.g. pipe, orifice, screen, etc.) one can measure data as the pressure drop across the device relative to the flow rate through the device. And from this data one ...
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Explaining the phenomenon relating to my cup of tea

I'm sitting in front of my computer and just made myself of cup of tea ("Brasilianische Limette") and see the water on the top evaporating into the room. But what caught my eye was a small rotating ...
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Pressure loss in an infinite pipe

I feel lost in this problem. I know pressure loss occurs in a pipe flow due to friction. Say given a constant diameter pipe, if we keep lengthening the pipe horizontally, and static pressure will ...
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156 views

reference request: 2D turbulence

I'm reading papers regarding the 2D Navier-Stokes equations. But I don't have a physics background. Would anybody come up with some introductory references of 2D turbulence which contain the following ...
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Does surface tension attenuate turbulence?

Rapids and several other "white water" systems could be typical examples of turbulent motion. To describe such flows the Navier-Stokes equations must be extended by terms describing the surface ...
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How to popularly describe typical features of a “non-linear system”

To quote Physics.SE tag definition: The term non-linear or nonlinear has several definitions but is generally used to describe a system that cannot be approximated by a superposition principle or ...
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195 views

Is the flow of a viscous fluid in free space under no pressure gradient always laminar?

Consider a (Newtonian) incompressible viscous fluid in three spatial dimensions, whose velocity field $\mathbb{v}=\mathbb{v}(x,y,z,t)$ moves according to the Navier-Stokes equations $$\tag{1}\label{...
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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.
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History of Turbulence suggestions

I am looking for extensive historical accounts of turbulence that ideally is strong in math and physics (at least giving references). Any suggestions? The only book I found is "A Voyage Through ...
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How is zonal flow defined and computed?

The transition to turbulence in pipe flow was recently observed to be in the same universality class as directed percolation. This was done by reinterpreting the turbulence and laminar flow in terms ...