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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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. Outline. Introduction Previous Researches Experimental Facilities and Data Processing - PowerPoint PPT PresentationTRANSCRIPT
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
2012 Cross-Strait Symposium on Applied Mechanics
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.
2012 Cross-Strait Symposium on Applied Mechanics
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
2012 Cross-Strait Symposium on Applied Mechanics
Turbulent Free Shear flow
Concentrated Efforts:
1. The control of aerodynamic noise
2. The enhancement of flow mixing effects
IntroductionIntroduction Previous Experimental Facilities Basic Flow Properties Spatial Development
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)
2012 Cross-Strait Symposium on Applied Mechanics
Turbulent free shear flow
IntroductionIntroduction Previous Experimental Facilities Basic Flow Properties Spatial Development
Ho and Nosseir (1981)
It is interpreted as the indicative of a structural origin of the Collective Interaction and Feedback Mechanism.
2012 Cross-Strait Symposium on Applied Mechanics
Turbulent Free Shear flow
IntroductionIntroduction Motivation Experimental Facilities Basic Flow Properties Spatial Development
Ho and Huang (1982)
Sub-harmonics and vortex merging in mixing layer
2012 Cross-Strait Symposium on Applied Mechanics
Turbulent free shear flow disturbance(Jet-Edge interaction)
IntroductionIntroduction Previous Experimental Facilities Basic Flow Properties Spatial Development
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
2012 Cross-Strait Symposium on Applied Mechanics
Introduction
Previous Researches
Experimental Facilities and Data Processing
Basic Flow Properties of Natural Jet
Spatial Development Impinging upon Cylinders
Spreading Characteristics of Impinging Jet
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.
2012 Cross-Strait Symposium on Applied Mechanics
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
2012 Cross-Strait Symposium on Applied Mechanics
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
2012 Cross-Strait Symposium on Applied Mechanics
Introduction
Previous Research
Experimental Facilities and Data Processing
Basic Flow Properties of Natural Jet
Spatial Development Impinging upon Cylinders
Spreading Characteristics of Impinging Jet
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
2012 Cross-Strait Symposium on Applied Mechanics
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
2012 Cross-Strait Symposium on Applied Mechanics
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%
2012 Cross-Strait Symposium on Applied Mechanics
Jet Tunnel and Forcing Equipment
Experimental FacilitiesIntroduction Previous Experimental Facilities Basic Flow Properties Spatial Development
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
2012 Cross-Strait Symposium on Applied Mechanics
Data Processing Hot-Wire anemometer calibration
Experimental FacilitiesIntroduction Previous Experimental Facilities Basic Flow Properties Spatial Development
King’s Law : U1/2 = a E2 + b
2012 Cross-Strait Symposium on Applied Mechanics
Introduction
Previous Research
Experimental Facilities and Data Processing
Basic Flow Properties of Natural Jet
Spatial Development Impinging upon Cylinders
Spreading Characteristics of Impinging Jet
Conclusions
Outline
2012 Cross-Strait Symposium on Applied Mechanics
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
2012 Cross-Strait Symposium on Applied Mechanics
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
2012 Cross-Strait Symposium on Applied Mechanics
Basic Flow Measurements Constant velocity contours of streamwise mean velocity
Basic Flow Properties of Natural jetIntroduction Previous Experimental Facilities Basic Flow Properties Spatial Development
2012 Cross-Strait Symposium on Applied Mechanics
Basic Flow Measurements Constant velocity contour of streamwise fluctuation velocity
Basic Flow Properties of Natural jetIntroduction Previous Experimental Facilities Basic Flow Properties Spatial Development
In the early stage of shear layer, the fluctuation flow tends to absorb energy from the mean flow.
2012 Cross-Strait Symposium on Applied Mechanics
Basic Flow Measurements Constant contour of transverse fluctuation velocity
Basic Flow Properties of Natural jetIntroduction Previous Experimental Facilities Basic Flow Properties Spatial Development
2012 Cross-Strait Symposium on Applied Mechanics
Basic Flow Measurements Spreading characteristics
• The entrainment phenomenon can explain from the momentum thickness, volume flow rate and shear layer width.
Basic Flow Properties of Natural jetIntroduction Previous Experimental Facilities Basic Flow Properties Spatial Development
2012 Cross-Strait Symposium on Applied Mechanics
Introduction
Previous Research
Experimental Facilities and Data Processing
Basic Flow Properties of Natural Jet
Spatial Development Impinging upon Cylinders
Spreading Characteristics of Impinging Jet
Conclusions
Outline
2012 Cross-Strait Symposium on Applied Mechanics
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.
2012 Cross-Strait Symposium on Applied Mechanics
Centerline Streamwise Fluctuation Velocity Distribution Cylinder diameter= 4mm , Xcy=4~5HSpatial Development of Impinging Jet
Experimental Facilities Basic Flow Properties Spatial Development Spread Feature Conclusions
The maximum fluctuation velocity region was clearly observed around the cylinder separation point.
2012 Cross-Strait Symposium on Applied Mechanics
Frequency Distribution of Jet-Cylinder Interaction Cylinder diameter= 4mm , Xcy=4~5HSpatial Development of Impinging Jet
Experimental Facilities Basic Flow Properties Spatial Development Spread Feature Conclusions
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
2012 Cross-Strait Symposium on Applied Mechanics
Introduction
Previous Research
Experimental Facilities and Data Processing
Basic Flow Properties of Natural Jet
Spatial Development Impinging upon Cylinders
Spreading Characteristics of Impinging Jet
Conclusions
Outline
2012 Cross-Strait Symposium on Applied Mechanics
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.
2012 Cross-Strait Symposium on Applied Mechanics
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.
2012 Cross-Strait Symposium on Applied Mechanics
Introduction
Motivation
Experimental Facilities and Data Processing
Basic Flow Properties of Natural Jet
Spatial Development Impinging upon Cylinders
Spreading Characteristics of impinging Jet
Conclusions
Outline
2012 Cross-Strait Symposium on Applied Mechanics
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