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Int. J. Turbomach. Propuls. Power 2018, 3(2), 11; https://doi.org/10.3390/ijtpp3020011

Vortex Structure and Kinematics of Encased Axial Turbomachines

Chair of Fluid Systems, Technische Universität Darmstadt, Otto-Berndt-Str. 2, 64287 Darmstadt, Germany
This paper is an extended version of our paper published in Proceedings of the 17th International Symposiumon Transport Phenomena and Dynamics of Rotating Machinery (ISROMAC 2017).
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Received: 26 January 2018 / Revised: 5 April 2018 / Accepted: 23 April 2018 / Published: 27 April 2018
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Abstract

This paper models the kinematics of the vortex system of an encased axial turbomachine at part load and overload applying analytical methods. Thus far, the influence of the casing and the tip clearance on the kinematics have been solved separately. The vortex system is composed of a hub, bound and tip vortices. For the nominal operating point φ φ opt and negligible induction, the tip vortices transform into a screw. For part load operation φ 0 the tip vortices wind up to a vortex ring, i.e., the pitch of the screw vanishes. The vortex ring itself is generated by bound vortices rotating at the angular frequency Ω . The hub vortex induces a velocity on the vortex ring causing a rotation at the sub-synchronous frequency Ω ind = 0.5 Ω . Besides, the vortex ring itself induces an axial velocity. Superimposed with the axial main flow this results in a stagnation point at the tube wall. This stagnation point may wrongly be interpreted as dynamic induced wall stall. For overload operation φ the vortex system of the turbomachine forms a horseshoe, i.e., the pitch of the screw becomes infinite. Both hub and tip vortices are semi-infinite, straight vortex filaments. The tip vortices rotate against the rotating direction of the turbomachine due to the induction of the hub vortex yielding the induced frequency Ω ind = 0.5 Ω / s with the tip clearance s. View Full-Text
Keywords: vortex dynamics; potential flow; part load; overload; sub-synchronous frequency; kinemtatic induced noise vortex dynamics; potential flow; part load; overload; sub-synchronous frequency; kinemtatic induced noise
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Pelz, P.F.; Taubert, P.; Cloos, F.-J. Vortex Structure and Kinematics of Encased Axial Turbomachines. Int. J. Turbomach. Propuls. Power 2018, 3, 11.

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