Fei-Bin Hsiao ( 蕭飛賓 ) and Cheng En Liu ( 劉承恩 ) 國立成功大學航空太空研究所

2012 Cross-Strait Symposium on Applied Mechanics

Vortical Structures and Spreading Characteristics of A Planar Jet Flow Impinging Upon a Cylinder平面噴流撞擊圓柱的渦流結構及擴散特性之研究

Fei-Bin Hsiao ( 蕭飛賓 ) and Cheng En Liu ( 劉承恩 )

國立成功大學航空太空研究所


Introduction

Previous Researches

Experimental Facilities and Data Processing

Basic Flow Properties of Natural Jet

Spatial Development of Jet Impingement Upon a Cylinder

Spreading Characteristics of Impinging Jet

Conclusions

Outline

2012 Cross-Strait Symposium on Applied MechanicsIntroductionIntroduction Previous Experimental Facilities Basic Flow Properties Spatial Development

Free shear flow is governed by the velocity gradient and considered to be inviscid.


Turbulent Free Shear flow

IntroductionIntroduction Previous Experimental Facilities Basic Flow Properties Spatial Development

Michalke (1964, 1965)

Inflexion point

Using the Hyperbolic-tangent velocity profile as a basic flow, the eigen values and eigen function can be computed numerically with the real frequencies and complex wave numbers



Concentrated Efforts:

1. The control of aerodynamic noise

2. The enhancement of flow mixing effects


Important features in 1970’s : 1. The large-scale coherent structures exhibited really the main features 2. The neighboring coherent structures would merge together 3. The edge tone phenomenon of the plane turbulent impinging jet was promisingAuthor : Crow and Champagne (1970) Brown and Roshko (1974) Winant and Browand (1974) Rockwell and Naudascher (1979)


Turbulent free shear flow


Ho and Nosseir (1981)

It is interpreted as the indicative of a structural origin of the Collective Interaction and Feedback Mechanism.



IntroductionIntroduction Motivation Experimental Facilities Basic Flow Properties Spatial Development

Ho and Huang (1982)

Sub-harmonics and vortex merging in mixing layer


Turbulent free shear flow disturbance(Jet-Edge interaction)


Kaykayoglu and Rockwell (1986)

The instantaneous pressure field of single frequency

2012 Cross-Strait Symposium on Applied MechanicsIntroductionIntroduction Previous Experimental Facilities Basic Flow Properties Spatial Development

Turbulent free shear flow disturbance(Jet-Edge interaction)

Kaykayoglu and Rockwell (1986)

Multiple frequency pressure fields


Introduction

Previous Researches



Spatial Development Impinging upon Cylinders


Conclusions

Outline

2012 Cross-Strait Symposium on Applied MechanicsPrevious ResearchIntroduction Previous Experimental Facilities Basic Flow Properties Spatial Development“ The Study of Self-Sustained Oscillating Plane Jet Flow Impinging Upon A Small Cylinder”Hsiao, Chou and Hunag, Journal of Experiments in Fluids, Vol. 27,pp.392-399 , 1999

The frequency jump-stage pattern of self-sustained oscillating flow was clearly observed in jet-small cylinder interaction in the potential core.


Introduction Previous Experimental Facilities Basic Flow Properties Spatial Development“Evolution of Coherent Structures and Feedback Mechanism of the Plane Jet Impinging On A Small Cylinder” Hsiao , Hsu and Huang, Journal of Sound and Vibration, Vol. 278, pp. 1163-1179, 2004

A modified feedback mechanism is proposed to successfully explain the interaction between the cylinder and the plane jet.

The competition between the jet and wake shear layer instabilities is significantly revealed in comparison with the standing wave number measured in the self-sustained oscillating flow.

Previous Research


To influence the flow structures after the end of the potential core with jet-

cylinder interaction.

To enhance the flow entrainment and spreading characteristics after the end

of the potential core.

To understand the interaction of the preferred mode frequency of plane jet

with the shedding frequency of cylinder after jet impingement.

MotivationIntroduction Motivation Experimental Facilities Basic Flow Properties Spatial Development


Introduction

Previous Research





Conclusions

Outline

2012 Cross-Strait Symposium on Applied MechanicsObjectivesIntroduction Previous Experimental Facilities Basic Flow Properties Spatial Development

Velocity Measurement

FFT power spectra

• Mean velocity

• Fluctuation velocity

•Velocity profiles

•Spreading characteristics


Flow Field System

ObjectionIntroduction Previous Experimental Facilities Basic Flow Properties Spatial Development

H

Near- field Transition region

Far-field

Natural jet 0 ~ 5 5 ~ 10 10 ~ 20

H H H H


Jet Tunnel and Forcing Equipment

Experimental FacilitiesIntroduction Previous Experimental Facilities Basic Flow Properties Spatial Development

U =10 m/s , H =12 mm

Reynolds number = 7.7 ×103

Turbulence intensity = 0.5%


Jet Tunnel and Forcing Equipment


Cylinder Diameter = 4mm, 8mm, 16mm

Cylinder locates at jet centerline and at the end of the potential core at Xcy = 4~5H

2012 Cross-Strait Symposium on Applied MechanicsExperimental FacilitiesIntroduction Previous Experimental Facilities Basic Flow Properties Spatial Development

NI DAQ

Pitto tube indicator

Hot-Wire anemometer


Data Processing Hot-Wire anemometer calibration


King’s Law : U1/2 = a E2 + b


Introduction

Previous Research





Conclusions

Outline


Basic Flow Conditions

Basic Flow Properties of Natural jetIntroduction Previous Experimental Facilities Basic Flow Properties Spatial Development

These results are well fitted with the theoretical value for laminar fow.

f0 α U0 3 / 2

θ 0 α U0 - 1/ 2

2012 Cross-Strait Symposium on Applied MechanicsBasic Flow Properties of Natural jetIntroduction Previous Experimental Facilities Basic Flow Properties Spatial Development

The initial flow field is laminar and turbulent intensity is less than 0.5%.

Basic Flow Conditions


Basic Flow Measurements

Basic Flow Properties of Natural jet

Because of the flow is laminar, so the velocity profile shows a top-hat shape. Whilethe flow gradually transforms to turbulent along downstream, the velocity profile becomes a bell shape shown above.

Introduction Previous Experimental Facilities Basic Flow Properties Spatial Development


Basic Flow Measurements Constant velocity contours of streamwise mean velocity



Basic Flow Measurements Constant velocity contour of streamwise fluctuation velocity


In the early stage of shear layer, the fluctuation flow tends to absorb energy from the mean flow.


Basic Flow Measurements Constant contour of transverse fluctuation velocity



Basic Flow Measurements Spreading characteristics

• The entrainment phenomenon can explain from the momentum thickness, volume flow rate and shear layer width.



Introduction

Previous Research





Conclusions

Outline


Centerline Streamwise Mean Velocity Distribution Cylinder diameter= 4mm , Xcy=4~5HSpatial Development of Impinging Jet

Experimental Facilities Basic Flow Properties Spatial Development Spread Feature Conclusions

The mean velocity profile was obviously affected due to existence of the downstream cylinder.


Centerline Streamwise Fluctuation Velocity Distribution Cylinder diameter= 4mm , Xcy=4~5HSpatial Development of Impinging Jet


The maximum fluctuation velocity region was clearly observed around the cylinder separation point.


Frequency Distribution of Jet-Cylinder Interaction Cylinder diameter= 4mm , Xcy=4~5HSpatial Development of Impinging Jet


The response frequency is dominant in the near-field region, while the one-quarter response frequency and the shedding frequency of cylinder are interacting at the end of the potential core.

Streamwise Transverse


Introduction

Previous Research





Conclusions

Outline


Spreading Characteristics Momentum thickness & Volume flow rate

Spreading Characteristic of Impinging JetExperimental Facilities Basic Flow Properties Spatial Development Spread Feature Conclusions

The momentum thickness and volume flow rate are obviously influenced after the jet impinging on the cylinder.


Experimental Facilities Basic Flow Properties ConclusionsSpatial Development Spread FeatureSpreading Characteristic of Impinging Jet

Spreading Characteristics Shear layer width

The shear layer width after jet-cylinder impingement is obviously influenced even after the impinging cylinder.


Introduction

Motivation




Spreading Characteristics of impinging Jet

Conclusions

Outline


The small cylinder located at the jet centerline and at the end of potential core

can truly influence the jet flow structures development even after the end of

potential core region.

From the velocity measurements, the fluctuation velocity and their kinetic

energy quickly transfer to the surrounding flow after the jet-cylinder

impingement.

The jet-cylinder interaction effectively induces the large-scale vortices which

enhances the jet spreading after the end of potential core and dominates the

whole following flow structures as well.

ConclusionsConclusionsExperimental Facilities Basic Flow Properties Spatial Development Spread Feature


Thank you for your attention

Fei-Bin Hsiao ( 蕭飛賓 ) and Cheng En Liu ( 劉承恩 ) 國立成功大學航空太空研究所

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Transcript of Fei-Bin Hsiao ( 蕭飛賓 ) and Cheng En Liu ( 劉承恩 ) 國立成功大學航空太空研究所

Fei-Bin Hsiao ( 蕭飛賓 ) and Cheng En Liu ( 劉承恩 ) 國立成功大學 航空太空研究所

Documents

Transcript of Fei-Bin Hsiao ( 蕭飛賓 ) and Cheng En Liu ( 劉承恩 ) 國立成功大學 航空太空研究所

Fei-Bin Hsiao ( 蕭飛賓 ) and Cheng En Liu ( 劉承恩 ) 國立成功大學航空太空研究所

Transcript of Fei-Bin Hsiao ( 蕭飛賓 ) and Cheng En Liu ( 劉承恩 ) 國立成功大學航空太空研究所