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The role of streamwise vorticity in the near-field entrainment of round jets

Liepmann, Dorian and Gharib, Morteza (1992) The role of streamwise vorticity in the near-field entrainment of round jets. Journal of Fluid Mechanics, 245 . pp. 643-668. ISSN 0022-1120. doi:10.1017/S0022112092000612.

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The role of streamwise vortex structures in the near-field (x/d < 10) evolution of a round jet is examined. In free shear layers the streamwise vorticity develops into Bernal-Roshko structures which are streamwise vortex pairs. Similar structures are shown to exist in round jets. These structures, which evolve and amplify in the braid region between primary vortical structures, are shown to drastically alter the entrainment process in the near field and to increase the rate at which fluid is entrained into the jet. As the flow evolves downstream, the efficiency of the streamwise vorticity in entraining fluid increases relative to that of the azimuthal vorticity. Beyond the end of the potential core regime, the entrainment process is mainly controlled by streamwise vorticity. These processes are identified via flow visualization and confirmed by detailed global entrainment measurements.

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Additional Information:© 1992 Cambridge University Press. Received 31 May 1991 and in revised form 26 June 1992. Published online: 26 April 2006. The authors gratefully acknowledge the help of C. Willert for the DPIV experiments. We also acknowledge constructive discussions with G. Broadwell, J. Lasheras, R. Moser, C. Pozrikidis, and A. Roshko. This work has been sponsored by DARPA through the URI program (contract number DARPA/ACMP N00014-86-K-0758) and ONR (contract number N00014-89-1529).
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Office of Naval Research (ONR)N00014-89-1529
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ID Code:41326
Deposited By: Tony Diaz
Deposited On:16 Sep 2013 21:06
Last Modified:10 Nov 2021 04:28

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