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EVOLUTION OF A COUNTER-ROTATING VORTEX PAIR IN A STABLY STRATIFIED FLUID

Keiko K. Nomura
Dept. of Applied Mechanics and Engineering Sciences University of California, San Diego La Jolla, CA 92093-0411, USA

Hideaki Tsutsui
Department of Mechanical and Aerospace Engineering, University of California, San Diego La Jolla, CA 92093-0411, U.S. A.

Daniel Mahoney
Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093-0411, U.S.A.

Julie Crockett
Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093-0411, U.S.A.; Department of Mechanical Engineering, Brigham Young University, Provo, Utah, 84602

James W. Rottman
Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093-0411, U.S.A.

Résumé

The evolution of a counter-rotating vortex pair in a stably stratified fluid is investigated using direct numerical simulations. The study focuses on the short-wavelength instability occurring in this flow and subsequent decay of the vortices. With stable stratification, the instability exhibits an earlier onset and higher growth rate than in an unstratified flow. This is due to the enhanced strain that occurs when the vortices move closer together as a result of the generated baroclinic torque. The decay of the vortex pair is enhanced with stratification due to additional mechanisms present in the flow. Secondary vertical vortex structures form between the primary vortices which enables exchange of fluid in the transverse direction. Detrainment of fluid from the primary vortices by the generated baroclinic torque also contributes to the breakdown of the flow. Computed energy spectra show the evolution of the primary instability, development of harmonics, and late time behavior.