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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9 views

Can we differentiate flows with identical Reynolds numbers but with different turbulence intensities?

The Reynolds number is given by $$\mathrm{Re} = \frac{v_{rms} L}{\nu}$$ Now imagine we fix $L$, $\nu$ and $v_{rms}$ - so the Reynolds number is constant. Imagine two different flows: $$(1): \bar{v} = ...
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Transition from laminar to turbulent flow

Is there a mathematically rigorous definition of turbulent or laminar flow? As far as I understand, laminar flow - means, that the velocity fields varies smoothly along the distance and time. Layers ...
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Turbulent boundary layer development

I'm currently working on my bachelor's thesis about the numerical simulation of a turbulent air flow through a rectangular channel. As part of that I'd like to compare my results to empirical ...
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Why is turbulence dissipation $\epsilon$ defined this way?

When deriving the turbulence kinetic energy equation $k$ by taking the trace of Reynolds stress transport PDE, this term appears : $$ 2\nu \overline{\frac{\partial u'_i}{\partial x_k}\frac{\partial u'...
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In turbulence what to we mean that an eddy has a wavenumber k?

In turbulence what to we mean that an eddy has a wavenumber k?
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Converting a turbulence spectrum in frequency to wavelength

So, I have a spectrum calculated from an underwater sensor, $S_{vv}(f)$, and want to convert it to $S_{vv}'(k)$, where $k$ is wavelength and $f$ frequency. I assume Taylor hypothesis for frozen ...
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Explanation of figure:turbulent magnetic field lines + spatial distribution of out-of-plane electric current density

The following graph is supposed to present turbulent magnetic field lines along with the spatial distribution of out-of-plane electric current density. However I am not sure I completely understand ...
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Can a Styrofoam box bounce back into a moving van?

I just came across this video. A styrofoam box falls out of a moving van, bounces off the road and lands back in the van. How can the box land back so precisely inside the van?! Usually, I would ...
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Initial Conditions for no-slip velocity (Walls)

For CFD initial condition, I want to know if i have to apply a very high velocity gradient on the wall of a pipe (internal flow) as it's the case when you study the freestream flow which surrounds an ...
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Calculate wind speed on each wind turbine on a wind farm considering consecutive wake effect

We, as a team, are working on a genetic algorithm related to wind farms layout and for this we obviously require to know the wind speed of each wind turbine given: Constant input wind speed. Same ...
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Is there a non-dimensional argument for a fluid’s characteristic force?

What the characteristic force is Dimensional analysis has an interesting result in fluid mechanics: the quantity $\chi=\eta^2/\rho$ has the units of force, where $\eta$ is the usual dynamic viscosity. ...
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Is there any relation between turbulent energy dissipation and pressure loss?

It is known that pressure loss depends on viscosity of fluid. However I learned today that energy dissipation rate in turbulent flow is independent of viscosity. It sounds like there is a ...
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Is it possible to solve for pressure loss in turbulent flow along a pipe purely analytically?

I understand it's possible to find pressure loss using formulas such as the Darcy Weisbach equation works with turbulence - but to my knowledge the friction factor is derived using empirical means. Is ...
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Why are aerodynamic / streamlined shapes always stumpy at the front?

I'm building an autonomous boat, to which I now add a keel below it with a weight at the bottom. I was wondering about the shape that weight should get. Most of the time aerodynamic shapes take some ...
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Reynolds number determines turbulent or laminar but Moody Chart has different interpretation

One can calculate the Reynolds number to determine whether or not flow is turbulent or not inside a pipe with circulating water. The formula is: $Re = \frac{\rho VD}{\mu}$ Let's say one gets $Re = 10,...
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Why does turbulent mixing result in a reduction of pressure and an increase in temperature?

For example, if i have a horizontal orifice plate in a tube and i'm pushing flow through it, there will be significant turbulent mixing downstream of the orifice plate. E.g. https://www.youtube.com/...
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What does near field shear layer mean?

I'm reading a research paper and the abstract is as follows... Ignition initiation by a turbulent hot jet involves complex transport and chemical processes with disparate and sensitive time scales. ...
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Some question regarding turbulent eddies

There's several concepts I don't have a clear understanding of: Plots of the turbulent energy cascade have a wave frequency as the axis - yet I see definitions of this "frequency" as the ...
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Turbulent Energy Cascade - Scale Between the Integral and Kolmogorov Microscale

I have seen derivations of the the length scale, time scale and characteristic velocity of eddies in the inertial or large-scale range and in the diffusive or Kolmogorov scale range. I'm interested ...
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How does water move out of the way/around an object moving under water?

Let's say a torpedo moved under the water. Water is virtually in-compressible right? So what happens to the water in front of the torpedo as it pushes forward? It has to somehow move out of the way, ...
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What is the structure on SUV's top back edge? [closed]

I see a lot of SUV's that has the structure as shown in the picture .I am talking about the the top back edge (right above the back window). Wont't it worsen the streamlined design and causing more ...
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What is the function for the magnitude of air resistance/drag?

In John Taylor's Classical Mechanics, he gives a basic treatment on air resistance/drag. In order to do this, he models air resistance as $\mathbf{f}=-f(v)\mathbf{\hat{v}}$, and then Taylor expands $f(...
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Why friction losses depend on velocity squared?

This is the reason that suction pipes of centrifugal pumps are most of the times much wider than the discharge pipes and that restriction of blood flow in arteries is always an alarming event. Does ...
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Confused about the direction of the Magnus effect force

From what I've read, the cause for the force acting as the result of the Magnus effect is the formation of a bended wake behind the moving sphere. Take a look at that picture: From that picture, it ...
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Can a theory of everything solve the oldest problem of turbulence? [closed]

Can a theory of everything solve the oldest problem of turbulence? Can we have unified theory of universe without solving the problem of turbulence?
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Is theoretically possible to have the laminar flow above $Re=10^7$?

The onset of turbulent flow ranges greatly, for pipe flow I came across the information that the onset of turbulent flow occurs at approximately $Re=10^4$, while for boundary layers on the airplane's ...
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How to simulate salinity gradient in experiment?

I feel like the question is probably fairly fundamental. I have to recreate oceanic turbulence in terms of salinity and temperature gradients. Temperature is easy - heater. What should I do with the ...
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Energy cascade in turbulence

I have studied that energy is transferred from larger eddy to smaller eddy and so on until that energy is converted into heat via viscous dissipation. 1. What i am not able to understand is why is ...
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Why turbulence is non-equilibrium?

I've encountered this notion many times that turbulence is non-equilibrium (e.g., Falkovich & Sreenivasan, Physics Today, 59, 2006). However, I am confused about what does it mean by "non-...
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Why does a running fan causes some soundproofing in the room?

I notice that when I switch on my fan inside my room, the room becomes soundproof to a great extent to the outside noises. The greater is the speed of the fan, the greater is the soundproofing. When ...
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Approximation of air resistance of rectangle with angle alpha

my problem is not that hard to explain, but maybe hard to model, because I couldnt find anything appropriate on the forum or internet..;D I need approximate the air resistance force of a rectangle ...
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Correlation function definition in hear transfer (statistical theory of turbulence)

I am trying to reproduce the approach in the paper by Nikishov. Since the paper is not easy to get I will just write out the statements here. They write the heat transfer equation for averaged ...
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From Kolmogorov (1941) to $k^{-5/3}$

I'm actually studying the famous paper of Kolmogorov (1941). I am trying to derive the passages that deduces the fact that the Energy spectrum has a dependency $k^{-5/3}$. As far as I know, the ...
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frequency wavenumber

Usually, when you have to go from frequency to wavenumber you have to adopt the following equation: $$k = \frac{2\pi f}{U}$$ where k is the wavenumber, f is the frequency and U is the velocity. ...
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Difference between alfven waves and magnetic fluctuations in solar corona

I have read in this paper https://arxiv.org/pdf/1911.07973.pdf about particles being accelerated in the solar corona either by Alfven waves (to my understanding when the turbulence is weak) or by ...
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How do we determine the flow regime during condensation without knowing the Reynolds number?

Condensation occurs in the mixed flow regime of a condensate film on a flat vertical plate. How does one determine the flow regime during condensation without knowing the Reynolds number? I know that ...
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Are the boundary and initial conditions only effecting parameters make turbulence unpredictable?

The book that I used to study turbulence states that "in a laboratory experiment initial and boundary conditions can not be fully under control, despite all the effort there will be infinitesimal ...
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Why traditional turbulence theory concerns so much about statistics such as correlations?

I have been wondering why the traditional turbulence theory, e.g., Kolmogorov's 1941 theory, concerns so much about things like two-point correlations, structure functions, their scalings, and so ...
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Modification of Mixing Length Damping Function to include Surface Roughness

Surface roughness has been incorporated into the van Driest damping function in studies by van Driest himself (1956) and more recently by Krogstad (1991) and Crimaldi et al (2006). These models ...
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Turbulence and the symmetries of Navier-Stokes

I am reading the book "Turbulence - The Legacy of A.N. Kolmogorov" by Frisch. He begins the book by introducing the different stages of fluid motion when the Reynolds number increases. In particular ...
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Behavior of parachutes in Crew Dragon launch escape experiment

When watching deployment of parachutes in SpaceX Crew Dragon Escape experiment, I noticed that sometimes parachutes collides with each other and later- separates. (Btw, you can watch this movie here, ...
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Reynolds number in General Relativity

Does the relativistic counterpart of the Reynolds number exist, and how can find it? And what is the dissipative term in Einstein equations?
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Good resource for Drag Coefficient vs Reynolds number (various shapes)?

The Wikipedia page on Drag Coefficient has a nice chart a little way down that shows the Drag Coefficient vs Reynolds number for a sphere, derived from experimental data. I am interested in looking at ...
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Physical interpretation of “Reynolds speed”

Reynolds number is the ratio of the fluid speed to some characteristic speed, $v_R = \frac{\mu}{\rho L}$ where $L$ is some characteristic length scale of the situation. Is there an intuitive ...
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Is there anything more chaotic than fluid turbulence?

Fluid turbulence is a highly complex and non-linear chaotic phenomenon. Great difficulties and complications are encountered when trying to accurately and robustly calculate or simulate fluid flows, ...
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Boiling water quites down [duplicate]

When I heat water in my electric kettle the noisy turbulence gets louder and louder as the water nears boiling. Shortly before the kettle turns itself off (presumably when it detects the temperature ...
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Why does water change from transparent to opaque when it comes out of a tap?

When we open the nozzle of the tap slowly, we observe a fine near-transparent beam of water particles coming down smoothly. If we loosen the nozzle a bit more, rotational effects start to appear, ...
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997 views

Bernoulli's law for turbulent flow

Is Bernoulli's law valid for turbulent flow for a non-viscous, non-compressible, non-rotating fluid with isoentropic flow? An ideal fluid has coeffieicent of viscosity=0,which implies that it's ...
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How do I determine the shape of steam?

When you dip a fork into a plate of hot food right off the stove and pull it out again with a forkful of food, it generates water vapour steam from the temperature difference. I am wondering how the ...
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Reynolds number in a wind tunnel

I would like to understand how to calculate the Reynolds number in the test chamber of a wind tunnel. It is known that the Reynolds number for a pipe is: $$Re = \frac{UL}{\nu}$$ where $U$ is the ...

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