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

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

Vanierschot, M. (Katholieke Universiteit Leuven)
Perçin, M.
van Oudheusden, B.W. (TU Delft Aerodynamics)

2016

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.

Swirling annular jet
Tomographic PIV
Pressure reconstruction
Vortex breakdown

http://resolver.tudelft.nl/uuid:c335c1d2-65a5-4596-9f76-05d1d0de5fd9

Springer

978-989-98777-8-8

Proceeedings of the 18th International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics: Lisbon, Portugal

18th International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics, 2016-07-04 → 2016-07-07, The Calouste Gulbenkian Foundation, Lisbon, Portugal

Institutional Repository

conference paper

© 2016 M. Vanierschot, M. Perçin, B.W. van Oudheusden