Hostname: page-component-848d4c4894-ndmmz Total loading time: 0 Render date: 2024-05-19T07:25:32.867Z Has data issue: false hasContentIssue false
  • English
  • Français

Measurements of spanwise scale change in a forced mixing layer

Published online by Cambridge University Press:  26 April 2006

Richard L. Leboeuf  and
Rabindra D. Mehta
Richard L. Leboeuf
Affiliation:
Center for Turbulence Research, Stanford University/NASA Ames Research Center, CA 94035, USA Fluid Mechanics Laboratory, NASA Ames Research Center, Moffett Field, CA 94035-1000, USA
Rabindra D. Mehta
Affiliation:
Department of Aeronautics and Astronautics, JIAA, Stanford University, Stanford, CA 94305-4035 USA Fluid Mechanics Laboratory, NASA Ames Research Center, Moffett Field, CA 94035-1000, USA
Get access Rights & Permissions [Opens in a new window]

Abstract

Spanwise scale changes of the streamwise vortical structure in a plane forced mixing layer have been investigated through direct measurements. Detailed three-dimensional phase-averaged measurements were obtained of the spanwise and streamwise vorticity in a forced mixing layer undergoing three spanwise roller pairings. A two-stream mixing layer with a velocity ratio (U2/U1) of 0.6 and laminar initial boundary layers was generated in a mixing-layer wind tunnel. Acoustic forcing, consisting of a fundamental roll-up frequency and its first, second and third subharmonics, was used to phase-lock the initial development and the first three pairings of the spanwise rollers. Although the overall spanwise scale remained unchanged through the first two roller pairings, some (cyclic) ‘readjustment’ of the weaker streamwise structures was observed. The overall spanwise scale doubled during the third roller pairing. For the first time, one of the proposed mechanisms for the scale change has been identified and its details measured directly. The weakest (positive) streamwise vortex is split into two and displaced by stronger neighbouring (negative) vortices. These two vortices (of the same sign) then merge together, thus doubling the spanwise scale and circulation of the resulting streamwise vortical structure.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 293 , 25 June 1995 , pp. 305 - 319
Copyright
© 1995 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

Bell, J. H. & Mehta, R. D. 1992 Measurements of the streamwise vortical structures in a plane mixing layer. J. Fluid Mech. 239, 213–248.Google Scholar
Bell, J. H. & Mehta, R. D. 1993 Effects of imposed spanwise perturbations on plane mixing-layer structure. J. Fluid Mech. 257, 33–63.Google Scholar
Bernal, L. P. & Roshko, A. 1986 Streamwise vortex structure in plane mixing layers. J. Fluid Mech. 170, 499–525.Google Scholar
Breidenthal, R. 1981 Structure in turbulent mixing layers and wakes using a chemical reaction. J. Fluid Mech. 109, 1–24.Google Scholar
Ho, C.-M. & Huerre, P. 1984 Perturbed free shear layers. Ann. Rev. Fluid Mech. 16, 365–424.Google Scholar
Huang, L.-S. & Ho, C.-M. 1990 Small-scale transition in a plane mixing layer. J. Fluid Mech. 210, 475–500.Google Scholar
Jimenez, J. 1983 A spanwise structure in the plane mixing layer. J. Fluid Mech. 132, 319–326.Google Scholar
Jimenez, J., Cogollos, M. & Bernal, L. P. 1985 A perspective view of the plane mixing layer. J. Fluid Mech. 152, 125–143.Google Scholar
Konrad, J. H. 1976 An experimental investigation of mixing in two-dimensional turbulent shear flows with applications to diffusion-limited chemical reactions. Project SQUID Tech. Rep. CIT-8-PU; and PhD thesis, California Institute of Technology, 1977.
Lasheras, J. C., Cho, J. S. & Maxworthy, T. 1986 On the origin and evolution of streamwise vortical structures in a plane, free shear layer. J. Fluid Mech. 172, 231–258.Google Scholar
Lasheras, J. C. & Choi, H. 1988 Three-dimensional instability of a plane free shear layer: an experimental study of the formation and evolution of streamwise vortices. J. Fluid Mech. 189, 53–86.Google Scholar
LeBoeuf, R. L. & Mehta, R. D. 1995a On using Taylor's hypothesis for three-dimensional mixing layers. Phys. Fluids, in press.Google Scholar
LeBoeuf, R. L. & Mehta, R. D. 1995b Vortical structure morphology in a forced mixing layer: initial roll-up and pairing. J. Fluid Mech. (Submitted).Google Scholar
Pierrehumbert, R. T. & Widnall, S. E. 1982 The two- and three-dimensional instabilities of a spatially periodic shear layer. J. Fluid Mech. 114, 59–82.Google Scholar
Rogers, M. M. & Moser, R. D. 1993 Spanwise scale selection in plane mixing layers. J. Fluid Mech. 247, 321–337.Google Scholar
Tung, C. H. 1992 Initial streamwise vorticity formation in a two-stream mixing layer. PhD dissertation, Department of Mechanical Engineering, University of Houston.