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An experimental study of an axisymmetric turbulent pulsed air jet

Published online by Cambridge University Press:  17 July 2009

I. CHOUTAPALLI ,
A. KROTHAPALLI  and
J. H. ARAKERI
I. CHOUTAPALLI*
Affiliation:
Department of Mechanical Engineering, 2525 Pottsdamer Street Florida A&M University and Florida State University, Tallahassee, FL 32310, USA
A. KROTHAPALLI
Affiliation:
Department of Mechanical Engineering, 2525 Pottsdamer Street Florida A&M University and Florida State University, Tallahassee, FL 32310, USA
J. H. ARAKERI
Affiliation:
Department of Mechanical Engineering, 2525 Pottsdamer Street Florida A&M University and Florida State University, Tallahassee, FL 32310, USA
*
†Email address for correspondence: cisaac@tamu.edu
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Abstract

An experimental study is carried out to elucidate the structure of a high Reynolds number (~105) turbulent pulsed jet. Particle image velocimetry measurements showed that the near flow field is dominated by a series of vortex rings with jet-like flows in between. The data show that the vortex rings convect at nearly constant speed of 0.6Uj (Uj: mean jet exit velocity) and the spacing between the rings assumes a value of about 0.6/St (St: Strouhal number=fd/Uj, where f is the pulsing frequency and d is the nozzle exit diameter). With increasing Strouhal number, the rings are closely spaced and the flow tends to assume a steady jet character at five diameters downstream of the nozzle exit. At lower Strouhal numbers there is a distinct region of jet flow in between the rings. Many of the global characteristics, entrainment, mass and momentum flux are essentially determined by the strength and spacing of the rings which, in turn, depend on St. We show that the increase in momentum is due to both increased momentum flux and overpressure at the exit in accordance with Krueger & Gharib (AIAA J., vol. 43 (4), 2005, p. 792). This increase in momentum comes at the expense of higher energy required to produce the jet. We also present results of organized and random components of the fluctuations and production of the random turbulence in a pulsed jet. The two regions of dominant turbulence production are identified with the ring and the trailing jet shear layers.

Type
Papers
Information
Journal of Fluid Mechanics , Volume 631 , 25 July 2009 , pp. 23 - 63
Copyright
Copyright © Cambridge University Press 2009

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Footnotes

‡

Present address: Department of Nuclear Engineering, Texas A & M University, College Station, TX 77843-3133, USA

Present address: Department of Mechanical Engineering, Indian Institute of Science, Bangalore, India

References

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