Physics of turbulence

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# Physics of turbulence - PowerPoint PPT Presentation

Physics of turbulence. muna Al_khaswneh Dr.Ahmad Al-salaymeh. Introduction. Turbulence cannot exist by itself, however; it requires a continuous supply of energy& changes in velocity& direction. Objective. The Definition of turbulence Examples of turbulence Boundary layer

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Physics of turbulence

muna Al_khaswneh

### Introduction

Turbulence cannot exist by itself, however; it requires a continuous supply of energy& changes in velocity& direction .

Objective
• The Definition of turbulence
• Examples of turbulence
• Boundary layer
• Study Reynolds numbers
• Study the differential continuity equation
• Study Navier-Stocks equation
• Kolmogorov theory
• Laminar-turbulent transition

Problems of turbulence

Definition & properties

It is a flow with disordered in time & space .

1-three-dimensionality.

3-strong vorticity.

4-Unpredictability.

Reynolds number

1. inertia forces 2. viscous forces

1. ρ u2 ,ρ: fluid density ,u : fluid speed

2. μ u , μ: viscous fluid , d : diameter fluid d

So that Reynolds number depend on fluid properties as ; speed , pipe diameter ,viscosity & density .
Laminar-turbulent transition

.

• Linear stability theory .
• Primary instability of free shear flow .
• Later stage of transition in free shear flows .
Continuity equation

The conservation of mass principle is applied to the control volume

Continuity equation

For three dimension (our interest )

z

Δz

y

Δy

Δx

x

= uxî + uyў +uzќ

Navier-stokes equation

the momentum translate with tow ways & tow forces

ways

• Convection transition
• Molecular transition

forces

1.Gravity force

2.Pressure force

Forces

1.Gravity force

Pressure force

Kolmogorov theory
• The physics of turbulence is the same in all turbulent system .
• It is independent of large scale forcing & small scale dissipative
• Fluctuation occur in an incompressible medium-density

4.Energy flows from large scales to small scales .

laminar

flow

(average

speed)

turbulent

pressure (drop)

Later stage of transition in free shear flows .

Some vorticity remains between the vortices , we will call it {secondary instability} .