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Experimental investigation of planar offset attaching jets with small offset distances

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Abstract

An experimental investigation was performed to characterize the development of planar jets initially issuing parallel to an adjacent wall with offset distances of up to 1 jet height and Reynolds number of 44,000. The results showed that the initial development of the mean flow field in the planar offset jets could be divided into five regions; three associated with the jet attaching to the wall similar to other reattaching shear layer flows and two associated with the resulting planar wall jet flow. The transition from the reattaching flow to the wall jet flow was also characterized by a significant change in the characteristic frequency, size, and convection velocity of the large-scale structures in the flows.

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Abbreviations

C P :

mean wall pressure coefficient, 2(P−P ∞)/ρ U 2 a

C p′ :

fluctuating wall pressure coefficient, 2p′/ρ U 2 a

f :

frequency, Hz

F pp :

power spectrum of the fluctuating pressure, Pa2/Hz

H s :

offset distance from the lower edge of the jet outlet to the wall, m

H j :

height of the jet, m

P :

mean pressure, Pa

p′:

RMS value of the fluctuating wall pressure, Pa

Re :

Reynolds number of the jet, U a H j /ν

U :

streamwise component of the local mean velocity, m/s

U max :

maximum local mean streamwise velocity, m/s

U a :

flow rate averaged velocity of the jet at the exit, m/s

u′:

RMS value of the streamwise fluctuating velocity, m/s

u′max :

maximum u′ along the inner shear layer, m/s

〈uv 〉:

turbulent Reynolds shear stress, m2/s2

W :

channel or facility width, m

X r :

attachment length, m

x :

spatial coordinate in the streamwise direction, m

x 1 :

location of the reference microphone in the two-point measurements, m

x 2 :

location of the second microphone in the two-point measurements, m

y :

spatial coordinate in the vertical direction, m

y +1/2 :

outer half width of the jet, m

z :

spatial coordinate in the cross-stream direction, m

θ o :

initial momentum thickness of the jet shear layer, m

ν:

kinematic viscosity of air, m2/s

ρ:

density of air, kg/m3

ρ pp :

correlation coefficient of the fluctuating wall pressure

ρ pu :

correlation coefficient of the fluctuating wall pressure and the streamwise fluctuating velocity

ρ pv :

correlation coefficient of the fluctuating wall pressure and the vertical fluctuating velocity

τ:

time interval, s

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Acknowledgments

This work was funded by the Natural Sciences and Engineering Research Council of Canada. The authors wish to acknowledge Prof. J. W. Naughton for his assistance in the measurements of the reattachment location, Dr. J. Hall for his suggestions, and Ms. L. C. Ofiara for her assistance in preparing the manuscript.

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Author notes

  1. Nan Gao

    Present address: School of Engineering, Sun Yat-sen University, Guangzhou, 510275, China

Authors and Affiliations

  1. Department of Mechanical Engineering, McMaster University, Hamilton, ON, Canada, L8S 4L7

    Nan Gao & Dan Ewing

  2. Queens University, Department of Mechanical and Materials Engineering, Kingston, Canada

    Dan Ewing

Authors
  1. Nan Gao
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  2. Dan Ewing
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Corresponding author

Correspondence to Dan Ewing.

Additional information

The research was funded by the Natural Sciences and Engineering Research Council of Canada.

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Gao, N., Ewing, D. Experimental investigation of planar offset attaching jets with small offset distances. Exp Fluids 42, 941–954 (2007). https://doi.org/10.1007/s00348-007-0305-3

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  • DOI: https://doi.org/10.1007/s00348-007-0305-3

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