Hostname: page-component-76fb5796d-x4r87 Total loading time: 0 Render date: 2024-04-25T13:55:41.345Z Has data issue: false hasContentIssue false
  • English
  • Français

Investigation of a co-flowing buoyant jet: experiments on the effect of Reynolds number and Richardson number

Published online by Cambridge University Press:  26 April 2006

E. R. Subbarao  and
B. J. Cantwell
E. R. Subbarao
Affiliation:
Department of Aeronautics and Astronautics, Stanford University, Stanford, CA 94305, USA Present Address: Hughes Aircraft Company. PO Box 92919, Los Angeles, CA 90009-2919, USA.
B. J. Cantwell
Affiliation:
Department of Aeronautics and Astronautics, Stanford University, Stanford, CA 94305, USA
Get access Rights & Permissions [Opens in a new window]

Abstract

Experiments have been carried out on a vertical jet of helium issuing into a co-flow of air at a fixed exit velocity ratio of 2.0. At all the experimental conditions studied, the flow exhibits a strong self-excited periodicity. The natural frequency behaviour of the jet, the underlying flow structure, and the transition to turbulence have been studied over a wide range of flow conditions. The experiments were conducted in a variable-pressure facility which made it possible to vary the Reynolds number and Richardson number independently. A stroboscopic schlieren system was used for flow visualization and single-component laser-Doppler anemometry was used to measure the axial component of velocity. The flow exhibits several interesting features. The presence of co-flow eliminates the random meandering typical of buoyant plumes in a quiescent environment. The periodicity of the helium jet under high-Richardson-number conditions is striking. Under these conditions transition to turbulence consists of a rapid but highly structured and repeatable breakdown and intermingling of jet and free-stream fluid. At Ri = 1.6 the three-dimensional structure of the flow is seen to repeat from cycle to cycle. The point of transition moves closer to the jet exit as either the Reynolds number or the Richardson number increases. The wavelength of the longitudinal instability increases with Richardson number. At low Richardson numbers, the natural frequency scales on an inertial timescale, τ1 = D/Uj where D is the jet diameter and Uj is the mean jet exit velocity. At high Richardson number, the natural frequency scales on a buoyancy timescale, τ2 = [ρjD/g(ρ∞ -ρj)]½ where g is the gravitational acceleration and ρj and ρ∞ are the jet and free-stream densities respectively. The transition from one flow regime to another occurs over a narrow range of Richardson numbers from 0.7 to 1. A buoyancy Strouhal number is used to correlate the high-Richardson-number frequency behaviour.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 245 , December 1992 , pp. 69 - 90
Copyright
© 1992 Cambridge University Press

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Ballantyne, A. & Bray K. N. C. 1977 Investigations into the structure of jet diffusion flames using time-resolved optical measurement techniques. Sixteenth (Intl) Symp. on Combustion, pp. 777–787. The Combustion Institute.
Becker, H. A. & Liang D. 1983 Soot emission, thermal radiation and laminar instabilities of acetylene diffusion flames. Combust. Flame 52, 247–256.Google Scholar
Chamberlin, D. S. & Rose A. 1928 The flicker of luminous flames. Ind. Engng Chem. 20, 1013–1016.Google Scholar
Chen, C. J. & Rodi. W. 1980 Vertical Turbulent Buoyant Jets: A review of Experimental Data. Permagon.
Fay J. A. 1973 Buoyant plumes and wakes. Ann. Rev. Fluid Mech. 5, 151–161.Google Scholar
Gebhart B., Hilder, D. S. & Kelleher M. 1984 The diffusion of turbulent buoyant jets. Adv. Heat Transfer 16, 1–57.Google Scholar
Grant, A. J. & Jones J. M. 1975 Low frequency diffusion flame oscillations. Combust. Flame 25, 153–160.Google Scholar
Kimura I. 1965 Stability of laminar jet flames. Tenth (Intl) Symp. on Combustion, pp. 1295–1300. The Combustion Institute.
Schonbucher A., Arnold B., Banhardt V., Bieller V., Kasper H., Kaufmann M., Lucas, R. & Schiess N. 1986 Simultaneous observation of organized density structures and the visible field in pool fires. Twenty-first (Intl) Symp. on Combustion, pp. 83–92. The Combustion Institute.
Strawa A. W. 1986 An experimental investigation of the structure of an acoustically excited diffusion flame. Ph.D. thesis, Stanford University, Department of Aeronautics and Astronautics.
Strawa, A. W. & Cantwell B. J. 1989 Investigation of an excited jet diffusion flame at elevated pressure. J. Fluid Mech. 200, 309–336.Google Scholar
Subbarao E. R. 1987 An experimental investigation of the effects of Reynolds number and Richardson number on the structure of a co-flowing buoyant jet. SUDAAR 563. Stanford University, Department of Aeronautics and Astronautics.
Zukoski E. E., Cetegen, B. M. & Kubota T. 1984 Visible structure of buoyant diffusion flames. Twentieth (Intl) Symp. on Combustion, pp. 361–366. The Combustion Institute.