What is Turbulence: Definition and 88 Discussions

In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between those layers.Turbulence is commonly observed in everyday phenomena such as surf, fast flowing rivers, billowing storm clouds, or smoke from a chimney, and most fluid flows occurring in nature or created in engineering applications are turbulent. Turbulence is caused by excessive kinetic energy in parts of a fluid flow, which overcomes the damping effect of the fluid's viscosity. For this reason turbulence is commonly realized in low viscosity fluids. In general terms, in turbulent flow, unsteady vortices appear of many sizes which interact with each other, consequently drag due to friction effects increases. This increases the energy needed to pump fluid through a pipe.
The onset of turbulence can be predicted by the dimensionless Reynolds number, the ratio of kinetic energy to viscous damping in a fluid flow. However, turbulence has long resisted detailed physical analysis, and the interactions within turbulence create a very complex phenomenon. Richard Feynman has described turbulence as the most important unsolved problem in classical physics.

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  1. D

    Creating turbulence in a small tube

    I have an odd question or a project I have been bouncing around in my head and I want to make sure that I am understanding the science of it all correctly. My question is will this cause turbulence in the larger chamber so that the air from the Yellow Question mark area is being pulled and mixed...
  2. rdemyan

    A How Does Anisotropy Affect the Calculation of Taylor Microscale in Turbulence?

    The Taylor microscale in isotropic turbulence is given by: $$\lambda = \sqrt{ 15 \frac{\nu \ v'^2}{\epsilon} }$$ where v' is the root mean square of the velocity fluctuations. In general, for velocity fluctuations in three dimensions: $$v' =...
  3. L

    A Will air turbulence in flexible airduct causes water condensation?

    In a normal aircond system using flexible airduct, assume airflow with temperature & humidity conditions (Tdry=23°C; Tdew=13.4°C; RH=55% ) go through a bended flexible airduct where air turbulence is formed: 1. Can condensation happens at the bended flexible airduct due to air turbulence? 2...
  4. C

    I Reynolds Number and Turbulence: Why Does Increasing Density Affect Flow?

    hi. I have a question regarding rheology. the Reynolds number increases when density of a fluid increases. so the flow becomes more turbulent. but I wonder why it is that the flow becomes more turbulent when density increases. why is that?
  5. G

    I Geometric Interpretation of Turbulence

    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 pushed by other layers of particles, then it must be that in addition to their translation, they...
  6. Astronuc

    I Jupiter atmosphere, turbulence and ocean fluid dynamics

    Ocean physics explain cyclones on Jupiter https://phys.org/news/2022-01-ocean-physics-cyclones-jupiter.html Moist convection drives an upscale energy transfer at Jovian high latitudes https://www.nature.com/articles/s41567-021-01458-y...
  7. M

    Turbulence of square fractal grid

    Hi all, Whats the significance/application of square fractal grid turbulence studies?
  8. Vashliana

    Turbulence and why eddy breakups take place?

    How to explain energy cascade mechanisms? Why eddy breakups take place?
  9. chaksome

    Can turbulence help measure liquid viscosity more accurately?

    Hi, all. Recently I plan to participate in an physics competition which focuses on viscosity measurements of liquid~I’ve investigted some kinds of methods such as capillary viscometers, Rotational viscometers, Vibrating Viscometers, co-flowing laminar viscometers and so on. I hope to find a...
  10. J

    Vortices and turbulence in square vs round pipe

    Greetings, I am about to start experimenting with misnamed rocket stoves and rocket mass heaters. I say misnamed because I think the velocities are too slow to be rocket science. (Why would I experiment with these? Because I have cement, perlite, and reinforcement materials at hand and I just...
  11. curiously new

    I Laminar-turbulent transition and Reynolds number

    Hi all! This is my first post here, so hopefully I am not in violation of any rules or etiquette. I'm looking to derive an equation for Reynolds number as function of pressure for a pinhole leak in a pressurized gas line. The line is regular air and is pressurized to 1 atmosphere and is leaking...
  12. K

    Why do we add turbulence to the rotating water in our experiment?

    <Mentor moved to Physics> My teacher talks about turbulence (2D and 3D), but I don't quite understand this. How is the turbulence different in the two buckets, and why does my teacher talk about turbulence but not diffusion? Is not diffusion the reason why the dye spreads in the water? I have...
  13. E

    Average velocity in a turbulent flow tube

    hi guys I'm really struggling to get the expression for average speed in turbulent flow The book explains absolutely nothing about how the integration is carried out, in addition to the fact that the logarithmic term becomes undefined when r = R what I did was carry out the integration up to...
  14. person123

    Is Turbulence Necessary for Lift on a Wing?

    For the wing of a plane, as an example, I think that the circulation around the wing due to faster flow on the top is balanced by the circulation of a vortex which is formed off of the tail. Since the greater speed on the top is necessary for the lift, would that also mean the turbulent flow...
  15. Twigg

    Physical Intuitions for the k-epsilon Turbulence Model

    Hey all! I am trying to understand the terms in the source-side of the k-epsilon transport equations. My only reference on this so far has been the wikipedia article (in my defense, it's not in Landau! the gospel has forsaken me :cry:). If you have a reference that goes into gory detail on the...
  16. N

    I Impact of atmospheric turbulence on secret key rate in QKD

    I have the calculation on secret key rate over the turbulence channel using Python code. The calculation is as below: import numpy as np import math import re import random import cmath #import itertools from math import pi,e,log import time #import xlwt import matplotlib.pyplot as plt from...
  17. nomadreid

    Requesting recommendations for specialized journal for....

    A physicist I know is looking to publish a paper on a special case of the Navier-Stokes equation; he submitted it to Physics Review Letters, who rejected it for two reasons: (1) it was too specialized, so not suitable for the broad readership that PRL targets, and (2) the physicist had made used...
  18. iamvksaini

    Flow Quality Impact on airfoil pressure distribution

    I have collected velocity data for a 3-D grid of test section of a low speed wind tunnel.I have tested airfoils for pressure distribution in the same test section for similar free stream conditions. How do I calculate the impact of flow quality in the test section on the test results of pressure...
  19. Domenico94

    Speed of fluid 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?
  20. Jimbecile

    Equipartition of magnetic fields and turbulence?

    Homework Statement You observe a molecular cloud core with the following properties: T = 5K R = 1pc M = 10 M⊙ n = 102 cm^-3 B = 1µG RΩ = 200 cms^-1 A. Assuming equipartition of B fields and turbulence, what is the turbulent velocity of the cloud? Homework Equations Emag=1/6((B^2R^3)/μo)...
  21. Domenico94

    I How does a fluid behave inside of a spherical cavity?

    Suppose you have a spherical cavity, with a flow of a fluid ( in particular water), entering it from one side. What will happen to this flow? Will it create turbulences? Will speed increase? Will eventual waves entering the cavity be reflected, so creating waves with bigger amplitude? Suppose...
  22. C

    Would there be turbulence around objects w/o boundary layers

    According to wikipedia "The onset of turbulence can be predicted by the Reynolds number, which is the ratio of inertial forces to viscous forces within a fluid which is subject to relative internal movement due to different fluid velocities, in what is known as a boundary layer in the case of a...
  23. JTC

    What causes pressure in form drag?

    Consider a ball flying through the air. When there is turbulence, and the flow separates, say on a SMOOTH ball, then in the rear, there is circulation in the wide wake. There is pressure on the front, but no pressure on the rear due to the fact that the fluid is "busy" circulating around. So...
  24. JTC

    A What is the difference between Flow and Boundary Separation?

    Could someone please go here... https://en.wikipedia.org/wiki/Flow_separation And explain to me the difference between Flow and Boundary Separation discussed in the opening. Because this explanation makes no sense to me. I have the problem. I just don't understand the difference.
  25. A

    Laminar to turbulent flow transition

    Is it true that the laminar to turbulent flow transition has been finally solved? From what I've read, it seems to be well described by the Directed Percolation Model. I can hardly believe it since I haven't seen the news in the press (from my point of view, it's a long standing unsolved issue...
  26. jamalkoiyess

    Computational Computational methods book for Turbulence

    Hello PF, I am currently searching for a good book that could give me insight into the computational methods for turbulence. In the lab we work on MATLAB and I already have the data for the flow but I am searching for ways to extract properties from it: flatness, skewness, some averages...
  27. JTC

    Golf ball and Tennis ball turbulence

    So I have read many articles on tennis ball fuzz and golf ball dimples and I am more confused than before. Here is one that says that the dimples make the golf balls go faster: https://entertainment.howstuffworks.com/sports/golf/basics/question37.htm And just when it makes all sense, I read...
  28. F

    CFD Modeling of Flue Gas Pollution Dispersion

    I've previously studied and used the k-epsilon turbulence model within Ansys to model water in a small stirred vessel. I am now interested in CFD models appropriate for modeling flue gas dispersion. I'd like to know: What additional considerations are required for modeling a gas as opposed to...
  29. J

    Inviscid flows and the turbulent (eddy) viscosity

    Hello, After Favre averaging the momentum equation for an inviscid flow, the following can be obtained: $$\frac{\partial}{\partial t} \left(\overline{\rho}\tilde{u}_i \right) + \frac{\partial}{\partial x_j}\left( \overline{\rho}\tilde{u}_i \tilde{u}_j \right) + \frac{\partial...
  30. S

    A Can the wave function show turbulence?

    I remember from my physics classes that the wave functions for the hydrogen atoms or an electron in a box showed typical linear wave behaviour. However, when you have a large system's wave function, say for example the universe, will it then show different spatial-dynamic structure? What comes...

    PBL Velocity Profile: Sinusoidal Variation w/ Height

    Why does the planetary boundary layer velocity profile shows a sinusoidal variation with height? Reference: Fig:14.10 Page 576 Fluid Mechanics - Kundu and Cohen 2nd edition
  32. Kevin Halagan

    Turbulence issues within tubing (Exair Vortex system)

    Hello, I used the Darcy Friction Factor from the Moody Diagram along with the Reynolds number to find energy losses inside the cold air tubing of our vortex system. My calculations showed that I should decrease transitions, length, diameter, and velocity. I am mainly concerned with the figuring...
  33. R

    What's after solving the turbulence problem?

    If physicists solved the turbulence flow problem what are the new things we will see in the physics world
  34. ATY

    Structure function in turbulence

    Hey guys, I need your help. I have to write a homework and we are actually looking at structure functions (Kolmogorov 41 and so on), but I have no clue what it does. So I have formulas, but I do not understand what a structure function is. Is it something in the "real world" or is it just a way...
  35. ATY

    How Accurate is the Integral Length Calculation in Turbulence Studies?

    . ##\require{color} \color{white} \colorbox{crimson} {Mod Note: to see images in this post displayed correctly, click on Reply and view this in editor}## Hey guys, I need your help. It is about the integral length of turbulence flow. So we got data from some wind measurement, recorded at...
  36. F

    Velocity fluctuations, variance and moment in turbulence

    I'm studying CFD and I'm on turbulence. It states that the fluctuating part of velocity squared and time averaged is the variance but variance in statistical terms is the deviation from the mean squared and averaged. So what is variance in turbulent fluctuating velocity? This variance is also...
  37. H

    Why Reynolds Stress vanishes on boundary of closed volume?

    The rate of working of the Reynolds Stress can be written as: where ui is the fluctuating velocity and Ūi is the time-averaged velocity. It is stated in the textbook that, if we integrate the above equation over a closed volume V, the divergence term on the left integrates to zero since τRij...
  38. H

    I Why is DNS more computationally expensive than k-ε?

    In the modelling of turbulent flows, DNS is often too computationally expensive. Therefore, we take a 'statistical' approach and use mean flow equations, which require closure on account of the Reynolds stress. One way to do that is through the Eddy Viscosity Hypothesis, and one of the ways of...
  39. H

    Chaos & Scales in Turbulent Flows

    Suppose you want to solve the Navier-Stokes equation for an incompressible turbulent flow. This is, in principle, possible. However, for higher Reynolds number, this isn't really feasible since the smallest eddy sizes are really small. First question 1) Why would this prevent you from...
  40. G

    How does Turbulence Intensity affect drag and flow separation?

    Just to the point.. How Turbulence Intensity affect a drag? As far as I know if there is decrease in Turbulence Intensity, the coefficient of drag will decrease to, but I don't know why the reason behind that. Also, the relationship with flow separation too. I hope someone can help me with...
  41. F

    Why Prandlt Mixing Length Theory works at all?

    There are several unreasonable assumptions in the formulation of the Prandlt Mixing Theory. However, it works reasonably well for simple 1-D flow. An attempt to explain why is given by Davidson in his book 'Turbulence', on page 122 - 124, section 4.1.4. It's stated that it still works because...
  42. Justice Hunter

    B Turbulence and Quantum Mechanical Probabilities

    So I'm a bit confused about the properties of wave mechanics, and trying to understand certain phenomena, which may be talked about, but I've never seen anyone talk about it. Here is the example. We have a bowl of water, a stick and a ball. We start with the ball, in which we drop it into the...
  43. M

    Head Loss and Pressure Rise During Gradual Expansion

    Homework Statement , There is an Head Loss question, two pipes join and expanding parts 30 degrees from the horizantal. Homework Equations The Attempt at a Solution Before attemting a solution I try to understand what a1=a2=1.06 is? Would you like to give some information about it...
  44. W

    Understanding the Relationship between Turbulence and the Reynold Number

    Homework Statement why the author gave that the complete turbulenece is indpendent on the Reynold number ?Homework EquationsThe Attempt at a Solution For the turbulence to occur , the Reynold number must be higher than certain value , am i right . So , IMO , turbulenet is dependent on the...
  45. N

    Is Turbulence at Point A Isotropic? Calculation Help

    Homework Statement Hello everyone, I am having a problem whether or not a turbulence at a specific location (let's say A) is isotropic or not. I have calculated the two root mean square values of velocity fluctuations measured at the point A in a fully developed turbulent pipe flow. the first...
  46. K

    Supply rate = dissipation rate in Turbulence

    So in many books, authors state that the supply rate, u^3/l is proportional to the dissipation rate ɛ, in a turbulent flow i.e: u^3/l ~ ɛ where u and l are characteristic velocity and length scales of the large eddies. Many will also state that the small scale eddies have a time period or...
  47. L

    Turbulent Viscosity: Definition & Effects on Flow

    whats turbulent viscocity?How it different from viscocity?Also i read that viscocity is fluid property.So has flow condition like laminar or turbulent has any effect on viscocity?
  48. K

    How Can Turbulence Dissipation Rate Be Independent of Viscosity?

    I've been reading about dissipation of energy in turbulent flows. I've read in various places about Richardson's idea of Energy cascade. But one of the biggest problems I have is understanding how the books (or texts online) all refer to ϵ, the rate of dissipation of kinetic energy, being...
  49. W

    Investing in Stock Markets: Fat Tails, Persistence, Multifractals & Turbulence

    Does anyone here know much about these topics? I understand they surround the absence of normally distrubted returns, excessive kurtosis. Fat tails somehow disprove the EMH? Can anyone explain this argument? I've been advised that there are links to turbulence in fluid dynamics, joined by the...
  50. M

    Reynolds Number and Turbulence in Atmospheric Boundary Layers

    Hi people! I'm studying the problem of a house in a valley with a wind at 5m/s. If I'd like to compute Reynolds number here and know if the flow is laminar or turbulent which is the charateristic dimension? The height of the house?