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 Mechanics Introduction Turbulent Shear Flow Free Shear Flow Jet Flow Mixing Layer Wake Flow Wall Shear Flow Boundary Layer Introduction PreviousExperimental FacilitiesBasic Flow PropertiesSpatial 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 Introduction PreviousExperimental FacilitiesBasic Flow PropertiesSpatial 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 Introduction PreviousExperimental FacilitiesBasic Flow PropertiesSpatial 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 promising Author : 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 Introduction PreviousExperimental FacilitiesBasic Flow PropertiesSpatial 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 Introduction MotivationExperimental FacilitiesBasic Flow PropertiesSpatial 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) Introduction PreviousExperimental FacilitiesBasic Flow PropertiesSpatial Development Kaykayoglu and Rockwell (1986) The instantaneous pressure field of single frequency

2012 Cross-Strait Symposium on Applied Mechanics Introduction PreviousExperimental FacilitiesBasic Flow PropertiesSpatial 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 Mechanics Previous Research Introduction Previous Experimental FacilitiesBasic Flow PropertiesSpatial 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 , 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 FacilitiesBasic Flow PropertiesSpatial 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 , 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. Motivation Introduction Motivation Experimental FacilitiesBasic Flow PropertiesSpatial 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 Objectives IntroductionPrevious Experimental Facilities Basic Flow PropertiesSpatial Development Velocity Measurement FFT power spectra Mean velocity Fluctuation velocity Velocity profiles Spreading characteristics

2012 Cross-Strait Symposium on Applied Mechanics  Flow Field System Objection IntroductionPrevious Experimental Facilities Basic Flow PropertiesSpatial Development H Near- fieldTransition region Far-field Natural jet0 ~ 55 ~ 1010 ~ 20 HHHH

2012 Cross-Strait Symposium on Applied Mechanics  Jet Tunnel and Forcing Equipment Experimental Facilities IntroductionPrevious Experimental Facilities Basic Flow PropertiesSpatial Development U =10 m/s, H =12 mm Reynolds number = 7.7 ×10 3 Turbulence intensity = 0.5%

2012 Cross-Strait Symposium on Applied Mechanics  Jet Tunnel and Forcing Equipment Experimental Facilities IntroductionPrevious Experimental Facilities Basic Flow PropertiesSpatial 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 Mechanics Experimental Facilities IntroductionPrevious Experimental Facilities Basic Flow PropertiesSpatial Development NI DAQ Pitto tube indicator Hot-Wire anemometer

2012 Cross-Strait Symposium on Applied Mechanics  Data Processing Hot-Wire anemometer calibration Experimental Facilities IntroductionPrevious Experimental Facilities Basic Flow PropertiesSpatial Development King’s Law : U 1/2 = a E 2 + 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 jet IntroductionPreviousExperimental Facilities Basic Flow Properties Spatial Development These results are well fitted with the theoretical value for laminar fow. f 0 α U 0 3 / 2 θ 0 α U 0 - 1/ 2

2012 Cross-Strait Symposium on Applied Mechanics Basic Flow Properties of Natural jet IntroductionPreviousExperimental 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. IntroductionPreviousExperimental 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 jet IntroductionPreviousExperimental 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 jet IntroductionPreviousExperimental 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 jet IntroductionPreviousExperimental 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 jet IntroductionPreviousExperimental 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=4~5H Spatial Development of Impinging Jet Experimental FacilitiesBasic Flow Properties Spatial Development Spread FeatureConclusions 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=4~5H Spatial Development of Impinging Jet Experimental FacilitiesBasic Flow Properties Spatial Development Spread FeatureConclusions 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=4~5H Spatial Development of Impinging Jet Experimental FacilitiesBasic Flow Properties Spatial Development Spread FeatureConclusions 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. StreamwiseTransverse

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 Jet Experimental FacilitiesBasic 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 FacilitiesBasic Flow PropertiesConclusions Spatial Development Spread Feature Spreading 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. Conclusions Experimental FacilitiesBasic Flow Properties Spatial Development Spread Feature

2012 Cross-Strait Symposium on Applied Mechanics Thank you for your attention