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Thermophysics and Aeromechanics

2005 year, number 2

Aerodynamic structure of unsteady swirling flow downstream of a sudden expansion

S.I. Shtork1, O. Comas2, E.C. Fernandes2, and M.V. Heitor2
1Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
2Department of Mechanical Engineering, Technical University of Lisbon, Portugal
Pages: 217-228

Abstract

Experimental study was performed for isothermal swirl flow behind an abrupt axisymmetric expansion resulting in development of instability in the form of precessing vortex core. LDA, high-speed video recording, and acoustic technique was used for study of instantaneous and averaged structure of unsteady flow. It was discovered that with an increase in the swirl number the flow evolved through typical stages, including the region of anomalous reduction of the precession frequency. Using the condition of helical symmetry of the flow [1], we demonstrated that this inversion in the frequency dependence occurs due to contribution from the axial movement of the helical vortex, with the helix pitch increasing with the swirl parameter.