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Dynamics and Bifurcations of Laminar Annular Swirling and Non-Swirling Jets
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2022-05-01
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Abstract:This paper presents bifurcation analyses characterising the nonlinear dynamics of fully developed laminar annular jets with respect to the centrebody diameter d, Reynolds number Re, and swirl ratio S. Similar flows appear in numerous applications and feature a vibrant range of topological and dynamical characteristics associated with phenomena including shear layer separation and vortex breakdown. Our results begin by describing the non-monotonic evolution of the axisymmetric jet’s steady topology under varying S. In accord with earlier reports, the jet progresses through a sequence of wake, breakdown and wall jet regimes in a qualitatively similar manner across a wide span of d and Re values. In the wake regime, the non-swirling jet bifurcates to a plane-symmetric, but not axisymmetric, steady flow pattern beyond a d-dependent critical Re value. With further increase in Re, the steady non-swirling jet destabilises subsequently via multiple distinct Hopf bifurcations. Introducing S > 0 to the jet also induces unsteadiness by twisting the singly azimuthally periodic (|m| = 1) asymmetric wake structure and causing it to precess periodically in time about the central axis. Intermediate swirl stabilises this unsteady dynamics and restores the jet’s axisymmetry. This stabilising effect is then reversed in the breakdown regime at higher S, where a variety of different |m| = 1 and |m| = 2 instabilities bifurcate from the steady flow as S is increased. Several instances of hysteresis and subcritical behaviour are reported and discussed, including one that manifests precessing vortex core oscillations.
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Content Notes:This is an open access article under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) license https://creativecommons.org/licenses/by/4.0/. Please cite this article as: Douglas, C., Emerson, B., & Lieuwen, T. (2022). Dynamics and bifurcations of laminar annular swirling and non-swirling jets. Journal of Fluid Mechanics, 943, A35. doi:10.1017/jfm.2022.453
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