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.
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...
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' =...
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...
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?
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...
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...
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...
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...
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...
<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...
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...
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...
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...
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...
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...
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...
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?
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)...
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...
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...
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...
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.
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...
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...
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...
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...
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...
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...
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...
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...
.
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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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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?
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...
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...
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?