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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26 views

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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784 views

How do speed and density change in a turbulent flow?

Suppose a fluid passes from having laminar flow, to having a turbulent flow (like when passing after an object). How do fluid speed and fluid density change after that?
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What is the structure on SUV's top back edge?

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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17 views

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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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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58 views

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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1answer
907 views

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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2k views

What is the turbulent Navier-Stokes equation for cylindrical coordinates?

I am looking for turbulent Navier Stokes equation for cylindrical coordinates. I know that RANS (Reynolds Averaged Navier Stokes) eq. is the solution, I understood the point of it but only for ...
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2answers
50 views

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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254 views

Which are the best books I can refer for turbulent heat transfer and its computation?

I am a graduate student. I wanted to do computation on heat transfer problem mainly heat convection. I am working on turbulent regime. Can you kindly suggest some good books so that I can get ...
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693 views

Kolmogorov/Energy spectrum for turbulent boundary layer

Previously, I have calculated energy spectrum for 3D isotropic turbulent flow data which is equally spaced in all three directions and then to compute the energy spectrum, one performs Fourier ...
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248 views

Turbulence in gravitational waves

I want to understand physical meaning and possible implications of few terms often used in physics specially with regards to gravitational waves / space-time fabric Space-time fabric is disturbed by ...
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293 views

Mathematical description of Bernoulli equation and transition from laminar to turbulent flow

I am very interested in the mathematical description of the next topics: 1. Bernoulli equation 2. Transition from laminar to turbulent flow Could you help me ...
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1answer
32 views

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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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 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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35 views

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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1answer
55 views

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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1answer
5k views

What is actually the characteristic length in fluid dynamics description?

In many fluid-dynamics models and quantities (Reynolds number, Strouhal number... generally various turbulent flow descriptions) there is a parameter (usually $L$ or $\ell$) descripted as ...
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32 views

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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320 views

How are the turbulent spectra determined in relativistic turbulence?

In a non-relativistic compressible fluid, the turbulent energy spectra are well-understood and appear to follow the Kolmogorov hypothesis. It would also appear that relativistic turbulence also ...
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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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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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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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3answers
136 views

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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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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What are premultiplied energy spectra?

When speaking about turbulence in fluid mechanics many times authors speak about "premultiplied energy spectra" but they never explain what really it is. I have searched for a definition but I did not ...
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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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1k views

Why do you feel air moving past you when you walk?

I know that when you walk through the air you form a wake vortex and turbulent air behind and the vortex grows the faster you walk. When I walk past people I almost feel wind that's behind them. So ...
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3answers
620 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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Estimating (or Modelling) an opening of vertically hinged door due to air flow

I am solving a simple looking, but actually difficult fluid dynamics problem. As shown, a hinged door is placed at the bottom of the box-shaped duct. Here, it is possible to assume any friction at ...
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48 views

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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56 views

When was any one liter of Long Island Sound water last in the Atlantic Ocean? [closed]

When was any one liter of Long Island Sound water last in the Atlantic Ocean? The Sound for this model is: Area: 1,268 mi² Mean depth: 63 feet Length 110 miles Eastern opening into the Atlantic is ...
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Most effecient negative shape to create laminar flow

I was looking at laminar flow filters to aid in my mycology work I'm doing. Most filters use an aluminum extrusion with fins. I figured the options out there are pretty expensive for what you get and ...
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562 views

Why are the backs of airplanes curved?

I get the front part, but why is the back curved too? I do not see a problem with the back being flat.
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How do I calculate the Reynolds number in multiphase flows?

I am modeling a gas flowing through a liquid. How do I calculate the Reynolds number in multiphase flows? And, at what Reynolds number should I consider the flow to be turbulent? The problem is of a ...
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What is enstrophy?

In turbulence, the enstrophy of a flow in a domain $\mathcal{D} \subset \mathbb{R}^{D}$ $$ \mathcal{E} = \int_{\mathcal{D}} |\vec{\nabla} \times \, \vec{v}|^2 d^{D}x $$ appears sometimes, it's cool ...
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Have we figured out how to analyze turbulent fluids?

I was surprised to read that we don't know how to analyze turbulent fluids. On page 3-9 of The Feynman Lectures on Physics (Volume One), Feynman writes: Finally, there is a physical problem that is ...
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How should energy loss in a hydraulic jump be calculated?

The energy loss in a hydraulic jump is still calculated with the old equation of Bresse from year 1860; (I.e., equation 7 in this paper from 2017) $$ \frac{\Delta E}{E_1} = \frac{(\sqrt{1+8Fr^2}-3)^3}...

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