Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session E28: Flow Instability: Nonlinear Dynamics and Global Modes II
5:10 PM–6:28 PM,
Sunday, November 18, 2018
Georgia World Congress Center
Room: B316
Chair: Roman Grigoriev, Georgia Institute of Technology
Abstract ID: BAPS.2018.DFD.E28.1
Abstract: E28.00001 : Spatiotemporal intermittency of global helical modes in low-density jets *
5:10 PM–5:23 PM
Presenter:
David D.W. Ren
(Hong Kong University of Science and Technology, University of California - Los Angeles)
Authors:
David D.W. Ren
(Hong Kong University of Science and Technology, University of California - Los Angeles)
Larry K.B. Li
(Hong Kong University of Science and Technology)
In previous experiments, we demonstrated that low-density jets issuing from long injectors can exhibit global instability in the form of self-excited helical oscillations. We found that decreasing the non-dimensional injector length $L_t^{-1}$ can cause the jet to transition from a global axisymmetric mode to a global helical mode. In the present study, we quantify the statistical properties of this transition by modelling the jet as a superposition of axisymmetric and helical eigenmodes whose amplitudes vary independently in time. Depending on $L_t^{-1}$ and the density ratio $S$, we find that the joint probability distribution of these modal amplitudes shows a statistical preference for axisymmetric or helical modes. We present evidence of intermittency using scaling laws for the ‘laminar’ phases and for the spectral density. We also demonstrate how the intermittency varies with spatial location, $L_t^{-1}$, and $S$. Finally, we use dynamic mode decomposition to extract the dominant frequencies of the axisymmetric and helical modes, yielding a universal frequency scaling for these modes in low-density jets.
*This work was funded by the Research Grants Council of Hong Kong (Projects 16235716 and 26202815) and HKUST’s Undergraduate Research Opportunities Program.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2018.DFD.E28.1
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