Shear layer instabilities in low-density transverse jets |
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Authors: | Daniel R Getsinger Cory Hendrickson Ann R Karagozian |
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Institution: | 1. Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, 46-147K Engineering IV, Los Angeles, CA, 90095-1597, USA
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Abstract: | The near-field shear layer instabilities forming in round transverse jets of variable (reduced) densities relative to the crossflow are investigated through gas-phase experiments. Jets composed of helium and nitrogen mixtures are injected from a converging nozzle mounted flush with an injection wall into air crossflow, allowing the jet-to-crossflow density ratio S to be varied between 1.00, the equidensity case, and 0.14, at constant jet Reynolds number Re j ?=?1,800. Jet-to-crossflow momentum flux ratios J are examined in the range $\infty>J\geq5$ at incremental values of the density ratio S. The results of single-component hotwire measurements in the jet shear layer indicate that a transition to global instability likely occurs as J is brought below approximately 10, and/or as S is brought below approximately 0.45?C0.40. This observation appears to link many previous independent studies of both equidensity transverse jets and low-density free jets, which may become globally unstable under alteration of J and S, respectively. However, the dynamical character of the transition to global instability in the low-density transverse jet displays differences under independent variation of J and S, which may indicate the predominance of different modes. |
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