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.E28.2
Abstract: E28.00002 : Precessing vortex core oscillations in a swirled jet - a weakly non-linear analysis*
5:23 PM–5:36 PM
Presenter:
Santosh Hemchandra
(Indian Institute of Science)
Authors:
Kiran Manoharan
(Indian Institute of Science)
Mark Frederick
(Pennsylvania State University)
Sean Clees
(Pennsylvania State University)
Jacqueline O'Connor
(Pennsylvania State University)
Santosh Hemchandra
(Indian Institute of Science)
Swirled jets at high swirl number (S), show the formation of a central recirculation zone (CRZ) due to vortex breakdown. At high S values, CRZ precession about the streamwise axis generates a precessing vortex core (PVC) with a characteristic precession frequency, fPVC. This occurs due to an internal feedback mechanism in the hydrodynamic field that results in coherent self-sustained flow oscillations.
We study the emergence of a PVC in a swirled jet (Re ~ 44000) where S is varied as a parameter for fixed net mass flow rate. Time resolved velocity field measurements are obtained using stereoscopic particle image velocimetry (sPIV) at 5 kHz. Wavelet and spatial cross spectral analysis of the data shows that a helical limit cycle flow oscillation emerges due to PVC formation at S=Sc=0.61. Global linear stability analysis using time averaged flow fields from sPIV accurately predicts fPVC at S=Sc. Predictions of fPVC for S > Sc from a weakly non-linear extension of linear theory agree well with experimental values. This confirms the fact that self-excited helical global modes can result in the emergence of PVCs through a supercritical Hopf bifurcation.
*Partial support from the National Center for Combustion Research and Development at IISc.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2018.DFD.E28.2
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