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 Q18: Vortex Dynamics and Instability
12:50 PM–3:26 PM,
Tuesday, November 20, 2018
Georgia World Congress Center
Room: B305
Chair: Arnab Samanta, Indian Institute of Science Banglore
Abstract ID: BAPS.2018.DFD.Q18.3
Abstract: Q18.00003 : Secondary Instability of Streamwise Vortices in a Turbulent Convex Wall Jet
1:16 PM–1:29 PM
Presenter:
Anshuman Pandey
(Ohio State Univ - Columbus)
Authors:
Anshuman Pandey
(Ohio State Univ - Columbus)
James W. Gregory
(Ohio State Univ - Columbus)
The outer part of a wall jet flowing over a convex wall satisfies the centrifugal instability criterion. Such a configuration has been studied in this work with a wall jet of air flowing over the exterior surface of a 0.91-m long circular cylinder. This flow scenario has found practical use in NOTAR helicopters for side force generation and in airfoil trailing edge designs for lift augmentation. As the convex wall jet evolves, centrifugal instability manifests itself in the form of unsteady streamwise vortices whose spanwise wavelength scales with wall jet thickness. These vortices enhance mixing between the wall jet and ambient flow and can be used as a control mechanism through appropriate use of secondary instability affecting them. In this work, micro-vortex generators are positioned at the wall jet nozzle lip in order to force stronger disturbances and preset the wavelength. Planar, stereo and TR-PIV have been conducted to characterize the evolution of the vortices. The coherent streamwise vortices undergo breakdown into non-coherent turbulence at a downstream location that depends on the preset vortex wavelength. Various decomposition techniques such as spatial FFT, POD and DMD have been used to study the modes of secondary instability leading to the breakdown process.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2018.DFD.Q18.3
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