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

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 Basic Flow Properties of Natural Jet Spatial Development of Jet Impingement Upon a Cylinder Spreading Characteristics of Impinging Jet Conclusions

Introduction Introduction Previous Experimental Facilities Basic Flow Properties Spatial Development Free shear flow is governed by the velocity gradient and considered to be inviscid.

Introduction Introduction Previous Experimental Facilities Basic Flow Properties Spatial Development 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 Inflexion point Turbulent Free Shear flow Michalke (1964, 1965)

Introduction Introduction 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 promising Author : Crow and Champagne (1970) Brown and Roshko (1974) Winant and Browand (1974) Rockwell and Naudascher (1979) Turbulent Free Shear flow Concentrated Efforts: 1. The control of aerodynamic noise 2. The enhancement of flow mixing effects

Introduction Introduction Previous Experimental Facilities Basic Flow Properties Spatial Development • It is interpreted as the indicative of a structural origin of the • Collective Interaction and Feedback Mechanism. Ho and Nosseir (1981) • Turbulent free shear flow

Introduction Introduction Motivation Experimental Facilities Basic Flow Properties Spatial Development • Sub-harmonics and vortex merging in mixing layer Turbulent Free Shear flow Ho and Huang (1982)

Introduction Introduction Previous Experimental Facilities Basic Flow Properties Spatial Development • The instantaneous pressure field of single frequency • Turbulent free shear flow disturbance(Jet-Edge interaction) Kaykayoglu and Rockwell (1986)

Introduction Introduction Previous Experimental Facilities Basic Flow Properties Spatial Development • Multiple frequency pressure fields • Turbulent free shear flow disturbance(Jet-Edge interaction) Kaykayoglu and Rockwell (1986)

Outline 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

Previous Research Introduction 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.

Previous Research 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.

Motivation Introduction Motivation Experimental Facilities Basic Flow Properties Spatial Development 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.

Outline 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

Objectives Introduction Previous Experimental Facilities Basic Flow Properties Spatial Development • Mean velocity • Fluctuation velocity Velocity Measurement • Velocity profiles • Spreading characteristics FFT power spectra

Objection Introduction Previous Experimental Facilities Basic Flow Properties Spatial Development H H H H H Flow Field System

Experimental Facilities Introduction 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

Experimental Facilities Introduction 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 Jet Tunnel and Forcing Equipment

Experimental Facilities Introduction Previous Experimental Facilities Basic Flow Properties Spatial Development NI DAQ Pitto tube indicator Hot-Wire anemometer

Experimental Facilities Introduction Previous Experimental Facilities Basic Flow Properties Spatial Development King’s Law : U1/2 = a E2 + b • Data Processing • Hot-Wire anemometer calibration

Basic Flow Properties of Natural jet Introduction Previous Experimental Facilities Basic Flow Properties Spatial Development f0 α U0 3 / 2 θ 0 α U0 - 1/ 2 These results are well fitted with the theoretical value for laminar fow. Basic Flow Conditions

Basic Flow Properties of Natural jet Introduction Previous Experimental Facilities Basic Flow Properties Spatial Development • Basic Flow Conditions The initial flow field is laminar and turbulent intensity is less than 0.5%.

Basic Flow Properties of Natural jet Introduction Previous Experimental Facilities Basic Flow Properties Spatial Development 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. Basic Flow Measurements

Basic Flow Properties of Natural jet Introduction Previous Experimental Facilities Basic Flow Properties Spatial Development • Basic Flow Measurements • Constant velocity contours of streamwise mean velocity

Basic Flow Properties of Natural jet Introduction 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. • Basic Flow Measurements • Constant velocity contour of streamwise fluctuation velocity

Basic Flow Properties of Natural jet Introduction Previous Experimental Facilities Basic Flow Properties Spatial Development • Basic Flow Measurements • Constant contour of transverse fluctuation velocity

Basic Flow Properties of Natural jet Introduction Previous Experimental Facilities Basic Flow Properties Spatial Development • Basic Flow Measurements • Spreading characteristics • The entrainment phenomenon can explain from the momentum thickness, volume flow rate and shear layer width.

Spatial 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 Mean Velocity Distribution • Cylinder diameter= 4mm , Xcy=4~5H

Spatial 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. • Centerline Streamwise Fluctuation Velocity Distribution • Cylinder diameter= 4mm , Xcy=4~5H

Spatial Development of Impinging Jet Experimental Facilities Basic Flow Properties Spatial Development Spread Feature Conclusions Streamwise Transverse 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. • Frequency Distribution of Jet-Cylinder Interaction • Cylinder diameter= 4mm , Xcy=4~5H

Spreading Characteristic of Impinging Jet Experimental 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. • Spreading Characteristics • Momentum thickness & Volume flow rate

Spreading Characteristic of Impinging Jet Experimental Facilities Basic Flow Properties Spatial Development Spread Feature Conclusions The shear layer width after jet-cylinder impingement is obviously influenced even after the impinging cylinder. • Spreading Characteristics • Shear layer width

Outline Introduction Motivation Experimental Facilities and Data Processing Basic Flow Properties of Natural Jet Spatial Development Impinging upon Cylinders Spreading Characteristics of impinging Jet Conclusions

Conclusions Experimental Facilities Basic Flow Properties Spatial Development Spread Feature Conclusions 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.

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