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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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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About the formula of the Taylor microscale

I am running simulations of a non-isotropic turbulent flow and I need to compute the Taylor microscale. The formula one can find in the book Turbulent flows (Stephen B. Pope) is : $\lambda = \sqrt{10} ...
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Can we really treat air and water flows the same?

Suppose we push water through a huge (0.1 m diameter) glass pipe and make an experimental Moody chart from slow (0.001 m/s laminar) to fast (10 m/s turbulent) speeds by measuring the pressure gradient....
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Statistically stationary, periodic random process

As I understand in a statistically stationary process, the statistics are invariant under a shift in time. It is natural to assume that the statistics are periodic in a periodic random process. If ...
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Turbulent boundary layer: viscous sublayer definition

I have seen different definitions of the viscous sublayer within a turbulent boundary layer, through my searches. Ones say that the viscous sublayer area is for $y \leq 10 * \delta_v$ where $\delta_v$...
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The motion of a spring due to wind (Wind induced oscillations)

Consider a spring held in the direction of wind as shown in the image. the spring body is wrapped with paper so that the spring oscillates with the wind in a circular manner. Is there any mathematical ...
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Why is flow more laminar in smaller tubes?

I was learning about laminar and turbulent flow in the context of breathing. This page emphasises how in larger tubes, like the trachea (main breathing tube of the body - responsible for Adam's apple) ...
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2D Kolmogorov-Obukhov Developed Turbulent Flow

Are there any references to the derivation of the Kolmogorov-Obukhov theory for fully developed turbulent flow in 2-dimensions? That is, the derivation of the Kolmogorov power rules, but in 2D? I was ...
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Is the transition from laminar flow to turbulent flow a kind of phase transition like those in condensed matter?

From the laminar flow to turbulent flow, is it a kind of phase transition? If so, what is the critical point? And what about the correlation length behaviours and fluctuation? Any critical exponents? ...
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Smoke and fluid mechanics

While lighting up a cigarette (I don't encourage smoking) I noticed that the flow of the smoke coming out of it, initially goes in a straight up direction, in a laminar flow, then about 10 cms above, ...
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How does turbulence arise from Navier-Stokes?

I would like to know how turbulence arises from the standard Navier-Stokes equations, both mathematically and also physically. At least I suspect this is the case as many of the "vanilla" ...
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Taylor's hypothesis in turbulence

Reading about Taylor's hypothesis for converting spatial to temporal scales and vice-versa, I understand that if $V$ is the bulk speed of the fluid then we could use: $$\ell = V \cdot \tau$$ To ...
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Turbulence geometric interpretation

I would like to give a geometric interpretation to turbulence. Let's take into consideration for example a Poiseuille flow. The velocity profile resembles a parabolic bullet. As the particles are ...
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Quasi-linear theory of plasma, some queries

I was studying about quasi linear theory of plasma turbulene and stuck at some questions (derivations), I could able to derive upto Eq.14 of this paper, but not sure how proceed for deriving the ...
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How does the temperature term in the refractive index structure parameter for optical turbulence relate to the temperature field?

I am trying to learn about atmospheric optical turbulence and have a question about the temperature dependence of the refractive index structure parameter. This parameter is a measure of optical ...
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Can we force turbulent transition of main flow despite unsufficient Reynolds number?

I was wondering something for awhile without finding what I was looking for : let's consider a flow, for instance inside a pipe, with a Reynolds number $Re$ below a critical Reynolds number $Re_{cr}$ ...
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Why do mosquito coil smoke not rise in a linear manner even if there is no wind?

I observed that when a mosquito coil is lit and kept on the floor then the smoke raises almost linearly but after some distance covered vertically, their path of motion gets completely distorted. It ...
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Resultant particle distribution function for mixing of two particle species

I would like to know if there is any way to compute the resultant particle distribution for system where two kinds of particles are mixed. For me one kind is Maxwellian and another is non-thermal ...
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What is the rationale-intuition for the "constant flux layer assumption", in atmospheric surface layer for turbent "diffusion"?

I wonder if, beyond the math, there is a physical intuition that I'm missing underlying this ubiquitous assumption of vertical constant fluxes in the surface layer (particularly in the inertial ...
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How do flat insect wings generate lift?

The traditional Bernoulli explanation of lift depends thoroughly upon a wing which, through differing geometry between the upper and lower wing surfaces, causes higher air velocity above and below, ...
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Question about Iroshnikov and Kraichnan spectrum

I'm currently reading articles about the IK model but I have a question: so δvk/vk is the change in magnitude in a single collision between wave packets, but why there is a square in the number of ...
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Test tank physics

In a test tank scaled-down simulation of, for example, a ship stability problem, is it not incorrect to assume that water will behave in a scaled-down fashion with regard to wave period? Don't we need ...
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Generalize power spectrum density to higher order spectral moment

If the power spectrum density for a given time series is given by : $PSD(f) = \frac{2 \Delta}{N} \sum_{j=1}^{N} \delta B^{2}(t_{j}, f)$, where, where $δB(t_{j} , f)$ is the magnitude of the trace ...
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Which object has lower drag? [duplicate]

Two same objects,only difference are parts that are paint in red,5m long,fluid air,veloctiy up to 300km/h. Which object has lower drag of these two and why(explanation)?
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Has car round back any aero advantages? [closed]

All Porsches have round back so much(top to down and also side to back) that people know to joke that car has lower drag when drive in reverse! Does so much round back has any aerodynamics advantages ...
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Why car has sharp separation edges at the back?

Most new cars that gain low drag have sharp separation edges at the back. If edges are round than wake is smaller but curvature produce low pressure, if edges are sharp wake is larger but dont have ...
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What does "marginality" mean in the context of magnetically confined plasmas?

I am reading the paper-Self-organized criticality and the dynamics of near-marginal turbulent transport in magnetically confined fusion plasmas by Sanchez and Newman. Here, the term "marginality&...
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How does object move in bottom of swimming pool? [closed]

Suppose there is an object $O$ (swimming goggles) that has fallen to the bottom of a swimming pool. I have the swimming pool circulation pump turned on. Initially, the object is at some position $P_1$....
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Why is an airfoil shaped like a teardrop?

I understand the reason airfoils are cambered on the top: to create lift. But one would assume this would result in aircraft wings having a semicircle-shaped design. Why is the cross-section of an ...
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Shell Models of Energy Cascade in Turbulence

I'm looking for introductory material on the subject of Shell Models in Turbulent flows. Text books are preferred, but if not, reviews could be helpful. This review is what I want to read, but it ...
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Transition from inertial to kinetic range in Solar wind turbulence

Most papers studying the turbulence in the solar wind present figures showing the power spectral density (PSD) of the magnetic field. The inertial range, with a power law index of ~ -5/3, is followed ...
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What makes the mixing of two fluids turbulent?

I am trying to grasp an intuitive idea for the formation of turbulence. Looking at the expression for the Reynold's number, I can see why increasing the flow rate of a fluid leads to turbulent ...
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Effect of Reynolds number on shear stress (skin friction drag)?

in this chart: we see that as Reynolds number increase, skin friction decreases for both layers (laminar and turbulent). now if we assume that increase in reynolds number is due to the increase in ...
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If the divergence of an isotropic vector field (in 3d Euclidean space) is a constant, what is it's dependence on the co-ordinates?

Basically the title. In symbols, I have \begin{equation} \nabla \cdot F = - 4 \varepsilon \ , \end{equation} where $\varepsilon$ is a constant, and there is isotropy. My guess was $F$ can depend ...
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Ideal Turbulence

I'm studying the turbulence in ocean and i started to study a mathematic introduction of turbulence. We define $ R_{ij}(\underline{x},\underline{r},t) := \overline{u_i(\underline{x},t)u_j(\underline{x}...
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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?
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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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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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Is there such thing as a non-turbulent wake?

We learnt in our fluids course that boundary layer separation can occur even for laminar non-turbulent flow (for high viscosity fluid). In this case, shown as ‘steady separation’ in the diagram below. ...
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