Visualization of the structure of vortex breakdown in free swirling jet flow

Conference paper (2016)

Authors

Vanierschot Katholieke Universiteit Leuven
van Oudheusden Aerodynamics - Aerospace Engineering
Research Group
Aerodynamics (Aerospace Engineering) (TU Delft)
Copyright: © 2016 M. Vanierschot, M. Perçin, B.W. van Oudheusden
Vortex breakdown Tomographic PIV Pressure reconstruction Swirling annular jet
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Published Date

2016

Language

English

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Faculty

Aerospace Engineering

Department

Flow Physics and Technology

Research Group

Aerodynamics

Abstract

In this paper we investigate the three dimensional flow structures in a free annular swirling jet flow undergoing vortex breakdown. The flow field is analyzed by means of time-resolved Tomographic Particle Image Velocimetry measurements. Both time-averaged and instantaneous flow structures are discussed, including a detailed analysis of the first and second order statistical moments. A Reynolds decomposition of the flow field shows that the time averaged flow is axisymmetric with regions of high anisotropic Reynolds stresses. Two recirculation zones exist with regions of very intensive mixing around them. Despite the axisymmetric nature of the time-averaged flow, a non-axisymmetric structure of the instantaneous flow is revealed, including a central vortex core which breaks up into a double helix. The winding sense of this double helix is opposite to the swirl direction and it is wrapped around the vortex breakdown bubble. The double helix precesses around the central axis of the flow with a precessing frequency corresponding to a Strouhal number of 0.13. To the authors’ knowledge, this structure of vortex breakdown has not been previously reported in the literature to occur for turbulent jet flow and it suggests that the well-known Precessing Vortex Core (PVC) found in swirling jets corresponds to the helical mode of vortex breakdown.