Разделы презентаций


Atmospheric turbulence презентация, доклад

Lecture 11. Atm. turbulenceSmall speed of motion. Particles move parallel each other. Laminar motion.Speed of the ink particle are faster than the speed of general motion. The ink jet starts meandering.

Слайды и текст этой презентации

Слайд 1Lecture 11. Atm. turbulence
Atmospheric turbulence
The atmosphere is known to be

in nonstop motion. Individual particles move randomly follow chaotic trajectories.




However,

basically the particles move in a certain direction.
This regime of motion is called turbulent regime of motion.
At this regime, the motion velocity pulsates. A moving particle sharply changes its velocity. Turbulent motion makes a remarkable impact on the state of the atmosphere and the physical processes in it.












Lecture 11. Atm. turbulenceAtmospheric turbulenceThe atmosphere is known to be in nonstop motion. Individual particles move randomly

Слайд 2Lecture 11. Atm. turbulence
Small speed of motion. Particles move parallel

each other. Laminar motion.

Speed of the ink particle are faster

than the speed of general motion. The ink jet starts meandering.








Fast motion. Trajectories of the motion distorted. That is turbulent motion.

Small vortexes produced by the turbulence are known as EDDIES.

Water-pipe tap is opened just slightly A small water jet is smooth (laminar motion).
Water pipe tap is opened widely The water jet is rough (Turbulent or eddy motion)

Lecture 11. Atm. turbulenceSmall speed of motion. Particles move parallel each other. Laminar motion.Speed of the ink

Слайд 3Lecture 11. Atm. turbulence
Laminar and turbulent flow of cigarette smoke
For

pipe flow, a Reynolds number above about 4000 will most

likely correspond to turbulent flow,
while a Reynold's number below 2100 indicates laminar flow.
The region in between (2100 < Re < 4000) is called the transition region.

Laminar and turbulent flow of cigarette smoke

Lecture 11. Atm. turbulenceLaminar and turbulent flow of cigarette smokeFor pipe flow, a Reynolds number above about

Слайд 4Lecture 11. Atm. turbulence
Theoretical and experimental studies have shown that

the character of liquid (gas) motion is suggested by Reynolds

Number.

Density of the liquid (gas)

Dynamic coefficient of molecular viscosity

Speed of motion

Distinctive (typical) scale of motion

In case ρ and η are constant (that is true for a certain medium), the number Re depends on the speed and distinctive scale of motion.

Critical value of the number Re is different for different substances and conditions. As the number of Re reaches its critical value, the motion is transferred into turbulent character.

Calculation Re numbers for the atmosphere suggested that the motion in the atmosphere are always turbulent.

Along with Re number there are some others criteria for character of motion and intensity of the eddy development.

Lecture 11. Atm. turbulenceTheoretical and experimental studies have shown that the character of liquid (gas) motion is

Слайд 5Lecture 11. Atm. turbulence
Turbulent motion of air results in disordered

and rapid fluctuation of meteorological parameters. However, along with chaotic

motion, all air particles are subjects to move with a mean speed. Therefore, momentary speed of motion c* can be presented as:

or

Mean speed

Pulsation

Notion of admixture specific content


A unit of air mass


Mass of water vapor


Mass of ozone


Mass of CO2


Mass of solid and liquid aerosols

Mass of a substance in a unit or air mass is called ADMIXTURE SPECIFIC CONTENT (ASC)

For instance, the water vapor content is known as specific humidity (s), or fraction of water vapor.

ASC vary in a wide range both in horizontal and vertical directions

Lecture 11. Atm. turbulenceTurbulent motion of air results in disordered and rapid fluctuation of meteorological parameters. However,

Слайд 6Lecture 11. Atm. turbulence
Eddy mole and mixing length
A separate particle

taking part in eddy mixing is called
EDDY (TURBULENT) MOLE.

Mean flow

Mixing

length


The heaven is infinity in time and space!

Any man is an insignificant particle in this infinity and boundlessness. What is the symbol of the infinity and boundlessness on the Earth? Certainly, it is the heaven! Any one appears from the infinity and goes into the infinity after his life is over, like an eddy mole, being formed in an atmospheric current, after a while mixes into the current and disappears there forever! (prof. G.G.Tarakanov)

Lecture 11. Atm. turbulenceEddy mole and mixing lengthA separate particle taking part in eddy mixing is calledEDDY

Слайд 7Lecture 11. Atm. turbulence
When moving, the eddy moles transfer admixture

and some physical properties of the air such as heat,

moisture, and momentum. The most remarkable mixing takes place in vertical direction.
Usually ASC decreases with height (∆s<0), but in some rare cases, it can be opposite (∆s>0). Eddy mixing results in equalization of ASC.

Z+∆Z

Z

Zi

s+∆s

s



The mass of admixture transferred by the eddy mixing for a unit of time through a unit of the surface at the altitude Zi is called FLUX OF ADMIXTURE (Q).

It is obvious that the eddy flux must be proportional to the difference of ASC at the level Z and ∆Z related to a unit of the distance between those levels, i. e.

Coefficient of eddy exchange (mixing coefficient)

Lecture 11. Atm. turbulenceWhen moving, the eddy moles transfer admixture and some physical properties of the air

Слайд 8Lecture 11. Atm. turbulence
Coefficients A and K are not constants.

Their value depend on: wind velocity and its variation, static

stability, properties of the underlying surface, etc

Postulate of eddy exchange

During an interval of time, the amount of transferred substances through a surface upward and downward must be equal.

Wind pulsation

Mixing length, L

A and K values


Lecture 11. Atm. turbulenceCoefficients A and K are not constants. Their value depend on: wind velocity and

Слайд 9Lecture 11. Atm. turbulence

Surface layer
The layer of the atmosphere, where

eddy coefficient increases with height is called SURFACE LAYER
20 m
The

most frequently S. L. height is 50 – 100 m

K values vary from to

There are also molecular fluxes of various substances

D is molecular diffusion coefficient

We may neglect molecular fluxes

Lecture 11. Atm. turbulenceSurface layerThe layer of the atmosphere, where eddy coefficient increases with height is called

Слайд 10Lecture 11. Atm. turbulence

Planetary boundary layer – k is close

to 0 (few km)

Surface layer – k increases (decimals –hundreds

of m)

Subsurface layer – laminar motion ( close to Earth surface, 2 mm)
Lecture 11. Atm. turbulencePlanetary boundary layer – k is close to 0 (few km)Surface layer – k

Слайд 11Lecture 11. Atm. turbulence
The surface layer is the layer in

a fluid where the scale of turbulent eddy is limited

by the eddies' proximity to an interface. The objects highlighted in white above are turbulent eddies whose size is constrained by the proximity of the center of each eddy to the surface.

The surface layer is the layer in a fluid where the scale of turbulent eddy is limited by the eddies' proximity to an interface. The objects highlighted in white above are turbulent eddies whose size is constrained by the proximity of the center of each eddy to the surface.

http://en.wikipedia.org/wiki/Surface_layer

Lecture 11. Atm. turbulenceThe surface layer is the layer in a fluid where the scale of turbulent

Слайд 12Lecture 11. Atm. turbulence
Eddy exchange in horizontal directions
Horizontal eddy mixing

can be neglected

Lecture 11. Atm. turbulenceEddy exchange in horizontal directionsHorizontal eddy mixing can be neglected

Слайд 13Lecture 11. Atm. turbulence

Semi empirical turbulent theory or “k” theory

is a theory based on eddy coefficient notion.

Lecture 11. Atm. turbulenceSemi empirical turbulent theory or “k” theory is a theory based on eddy coefficient

Обратная связь

Если не удалось найти и скачать доклад-презентацию, Вы можете заказать его на нашем сайте. Мы постараемся найти нужный Вам материал и отправим по электронной почте. Не стесняйтесь обращаться к нам, если у вас возникли вопросы или пожелания:

Email: Нажмите что бы посмотреть 

Что такое TheSlide.ru?

Это сайт презентации, докладов, проектов в PowerPoint. Здесь удобно  хранить и делиться своими презентациями с другими пользователями.


Для правообладателей

Яндекс.Метрика