Application of Turbulence Edited

8/3/2019 Application of Turbulence Edited

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PRACTICAL APPLICATIONS

OF TURBULENCE

CHETHAN P BHAT (080922016)

KIRAN R (080922018)

MANJESH B (080922019)

NARENDRA N PAI (080922022)

SREEBHASH S KUTTY (080930001)

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INTRODUCTION

An important characteristic of turbulence is itsability to transport and mix fluid much moreeffectively than a comparable laminar flow

The effectiveness of turbulence for transportingand mixing fluids is of prime importance in manyapplications

Turbulence is also effective at 'mixing' themomentum of the fluid

Compared with laminar flow, rates of heat andmass transfer at solid-fluid and liquid-gas interfacesare much enhanced in turbulent flows

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The major motivation for the study of turbulent flowsis the combination of the three precedingobservations:

1. The vast majority of flows is turbulent

2. The transport and mixing of matter, momentum, and

heat in flows is of great practical importance3. Turbulence greatly enhances the rates of these

processes

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AREAS OF APPLICATION

In the processing of liquids or gases with pumps,compressors, pipe lines

The flows around vehicles - e.g., airplanes,automobiles, ships, and submarines

The mixing of fuel and air in engines, boilers, andfurnaces, and the mixing of the reactants inchemical reactors

Pollutant streams released into the atmosphere orinto bodies of water

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The boundary layer in the earth's atmosphere

Jet streams in the upper troposphere; cumulusclouds in motion

The water currents below the surface of theoceans

Gulf Stream is a turbulent wall-jet kind of flow

The photosphere of the sun and the photospheresof similar stars are in turbulent motion

Interstellar gas clouds (gaseous nebulae), the wakeof the earth in the solar wind

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Chemical engineers use turbulence to mix and

homogenize fluid mixtures and to acceleratechemical reaction rates in liquids or gases

Turbulence increases heat transfer rates inmachinery of all kinds

The rates of transfer and mixing are several ordersof magnitude greater than the rates due tomolecular diffusion

Used in flowmeters, heat exchangers and other

devices The diffusivity of turbulence, which causes rapid

mixing and increased rates of momentum, heat,and mass transfer, is another important feature ofall turbulent flows.

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It is the source of the resistance of flow in pipelines.

it increases momentum transfer between winds and

ocean currents The outstanding characteristic of turbulent motion is its

ability to transport or mix momentum, kinetic energy, andcontaminants such as heat, particles, and moisture.

A new research has suggested that that turbulence

plays a critical role in creating ripe conditions for thebirth of planets, a notion that challenges the prevailingtheory of planet formation. Which was before describedby Gravitational instability.

Without turbulence, the mixing of air and fuel in an

automobile engine would not occur on useful timescales

Heat transfer and combustion rates

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As a practical matter, turbulence plays an importantrole in technology and control phenomena such as

weather and climate that have a large effect onhuman activities.

Predictability of the Earths atmosphere .

The transport and dispersion of heat, pollutants,

and momentum in the atmosphere and oceanswould be far weaker.

The mixing of air and fuel in an automobile engineat proper intervals.

Life as we know it would not be possible on Earth.

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TURBULENT COMBUSTION

Combustion always takes place within a turbulentflow field for two reasons:

1. Turbulence increases the mixing process andenhances combustion and combustion releases heat

2. Generates flow instability through gas expansion andbuoyancy, thus enhancing the transition to turbulence

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ROTAMETER

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Float is sharp edgedEffect of viscosity variation

made insensitive by makingflow over float turbulent


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HEAT EXCHANGERS

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Turbulent flow have ahigher heat transfercoefficient

According to SeiderTata equation

For laminar flow

h Re1/3

For turbulent flowh Re0.8
http://en.wikipedia.org/wiki/File:Tubular_heat_exchanger.png


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STABLY-STRATIFIED TURBULENCE

Example of real turbulent flow

Naturally occuring in atmosphere, oceans etc

A three-dimensional homogeneous turbulence

submitted to a stable stratification This is no longer an isotropic turbulence ,which is a

ideal turbulence

Has important applications in meteorology and

oceanography

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In the atmosphere, small-scale three-dimensionalturbulence, produced by the breaking of lee wavesbehind the mountains or by convective storms, mayfind itself afterwards imbedded in a stably-stratified

density field and collapse into quasi two-dimensional turbulence.

In the ocean, the interaction of gravity waves withthree-dimensional turbulence involves various

complex phenomena which contribute to theformation of the mixed layer and are responsible forvertical exchanges arising in this layer and at thelevel of the thermocline 13


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HORIZONTAL VORTICITY ISOSURFACES

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The vertical mixing layersthus created cause a strongvertical dissipation whichinhibits any importantinverse energy cascade

within the horizontal layers. A similar structure of quasi

horizontal vortex sheetswas found in experimentsby Fincham, where a rakeof vertical rods was towed

through a horizontalstratified tank.


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ROTATING TURBULENCE

This has applications in geophysical flows as wellas in engineering (turbomachinery)

The turbulent characteristics of the flow in bladepassages of radial pumps and compressorimpellers determine the efficiency of these devices

Turbulence is also of great importance for thecooling by the fluid inside the blades

Effects in geophysical and astrophysicalphenomena

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Galaxies look strikingly like the eddies which areobserved in turbulent flows such as the mixing layerbetween two flows of different velocity, and arecalled the eddies of a turbulent universe

The atmospheres of planets such as Jupiter andSaturn, the solar atmosphere or the Earths outer

core are turbulent

Small-scale turbulence in the atmosphere can be

an obstacle towards the accuracy of astronomicobservations, and observatory locations have to bechosen in consequence

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SEPARATED FLOWS TURBULENCE

Separated flows are very common in externalaerodynamics of cars, trains, planes, ships or submarines

Large-eddy simulation techniques are now able to handlethese flows both statistically and from the coherent-vortexpoint of view

Also encountered in hydraulics, thermo hydraulics ofnuclear reactors, or internal aerodynamics of combustors(rocket solid-propergol boosters).

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The flow behind a two-dimensional backward-facingstep is a prototype of separated flow

Rotating back step is an interesting combination ofrotation and separation

A geophysical example of backstep in a shallowflow is given by the vortices shed in the Algeriancurrent, which detach periodically from therecirculation region induced by surface Atlantic

water passing through Gibraltar straight to theMediterranean

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COMPRESSIBLE FLOWS

The development of hypersonic planes and bodieshas boosted research on free shear or wallturbulent flows in supersonic or hypersonicconditions

Compressible turbulence may be characterized bythe nature of the instantaneous velocity field

Compressibility inhibits the development ofinflectional instabilities


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In many supersonic situations without heat sources,it may be expected that the divergence freeapproximation will be good enough to describe theturbulence of the shear flows

In supersonic flows, many studies have beendevoted to shock/boundary layer interactions

The study of shock/boundary layer interactions is amust for external aerodynamics


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VORTEX FLOW METERS

Vortex flow meters uses the principle of vortexshedding

The vortex shedding results in pressure andvelocity changes around and downstream of the

vortex element

Placing pressure, thermal or ultrasound detectors ina location where signal is high the vortex sheddingfrequency is measured


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CONCLUSION

A turbulent flow is unpredictable

Is by nature unstable

Is rotational i.e. their vorticity is non zero

Turbulent flows always occur when the Reynoldsnumber is large

Turbulence also has undesirable consequences

It increases energy consumption of pipelines,

aircraft, ships, and automobiles and is an aspect tobe reckoned with in air-travel safety, and it distortsthe propagation of electromagnetic signals, and soforth


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A major goal of a turbulence practitioner is theprediction and control of the effects of turbulence invarious applications such as industrial mixers andburners, nuclear reactors, aircraft intakes, around

ships, and inside of rocket nozzles A major goal of a physicist working in turbulence is

to understand the dynamical origin of thiscomplexity, describe and quantify its features, and

understand the universal properties embedded infeatures that are specific to a flow


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A larger goal is to understand whether the statisticalcomplexity of turbulence is shared in a serious wayby other phenomena such as granular flows,fractures, and earthquakes


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REFERENCES

1. Turbulence in Fluids, MARCEL LESIEUR, Springer

2. An Informal Introduction to Turbulence, ARKADYTSINOBER, Kluwer Academic Publishers

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THANK YOU

Date post:	06-Apr-2018
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Application of Turbulence Edited

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