PIV measurement of the attached plane jet velocity field at a high turbulence

PIV measurement of the attached plane jet velocity field at a high turbulence intensity level in a room

Guangyu Cao a,b,*,Markku Sivukari b ,Jarek Kurnitski c ,Mika Ruponen d

a

Technical Research Centre of Finland (VTT),Vuorimiehentie 5,Espoo 02044,Finland b

Department of Energy Technology,Aalto University,Otakaari 4,Espoo 02150,Finland c

Finnish Innovation Fund,Itämerentori 2,Helsinki 00181,Finland d

Halton Oy,Haltonintie 1–3,Kausala 47400,Finland

a r t i c l e i n f o Article history:

Received 8June 2009

Received in revised form 6April 2010Accepted 19April 2010

Keywords:PIV

Attached plane jet Jet velocity

Turbulence intensity

a b s t r a c t

The behaviour of an attached plane jet at high turbulence intensity (>20%)is not completely understood,especially at relatively low Reynolds numbers (<2000)in a room.This study focuses on the detailed mean and instantaneous jet flow field using the particle image velocimetry (PIV)measurement technique in a full-scale climate chamber.Three isothermal conditions at different Reynolds numbers based on the jet slot height and slot average velocity,960,1320and 1680,were measured,having a turbulence intensity of 44%,30%and 22%,respectively.The results show that the measured jet velocity was able to match the earlier empirical turbulent jet results when the turbulence intensity was of the order of 40%.Incomplete self-similarity occurs when the turbulence intensity is less than 30%.After a few slot heights downstream from the jet slot,most of the data of the jet at the Reynolds number 960present self-similarity characteristics.

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1.Introduction

The attached plane jet,also called the two-dimensional wall jet,has been studied for many decades in different engineering appli-cations (Glauert,1956;Rajaratnam,1976;Abrahamsson,1997;Zou,2001).In practical engineering applications,attached plane jet discharging is a common application used for the ventilation or air conditioning in a room (Karimipanah,1996).The discharging jet flow from diffusers is designed to attach to the ceiling or the wall surface,so that the high-velocity region is restricted outside the occupied zone (Goodfellow and Tähti,2001;Cao et al.,2007,2008).After the jet exits from the opening,the potential core of the jet,which represents a short distance from the jet slot preserv-ing the jet slot velocity,is consumed at the point where the bound-ary layer growth on the surface meets the shear layer expansion at the free boundary (Awbi,1991).The downstream jet core flow undergoes a transition process and becomes fully developed.1.1.Self-similarity and jet zones of the attached plane jet

The earliest known work on the attached plane jet was carried out by Förthmann (1934),described and quoted in Schwarz and Cosart (1961),Rajaratnam (1976),and Awbi (1991).The first theo-retical investigation of the incompressible isothermal laminar at-tached plane jet was undertaken by Tetervin (1948),presented in Quintana et al.(1997).Tetervin predicted that the boundary layer thickness of the attached jet would grow and the local maximum velocity would decay with the downstream distance as x 0.75and x À0.5,respectively.Generally,the non-dimensional jet velocity pro-files should be similar at a different distance from the jet slot in the fully developed zone of the turbulent jet.This refers to the self-similarity of the jet,which is one of the characteristics of the tur-bulent jet in the fully developed zone (Rajaratnam,1976;Awbi,1991).Glauert (1956)achieved a similarity solution for the laminar and turbulent radial and attached plane jet.Bajura and Szewczyk (1970)carried out an experimental investigation on laminar wall jets and obtained good agreement with Glauert’s similarity solu-tion in the laminar condition.Under non-isothermal conditions,the different jet zones have been identified by experimental stud-ies and found to be dependent on the initial conditions,including the slot Reynolds number and the initial Archimedes number (Cao et al.,2009a ).

Generally,a four-zone division into the potential core zone,transition zone,fully developed turbulent zone,and the terminal zone was used to describe the free jet flow field by Tuve (1953),ci-ted by Hagström et al.(1999)and Goodfellow and Tähti (2001).As for the classification of the attached plane jet zones,only two zones,the potential core zone and the characteristic decay zone,were presented by Awbi (1991)under isothermal conditions.Under non-isothermal conditions,a three-zone division into the

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*Corresponding author at:P.O.Box 1000,FI-02044VTT,Finland.Tel.:+358401993513;mobile:+358503902475;fax:+358207227015.

E-mail address:guangyu.cao@vtt.fi(G.Cao).