Characterizing the Unsteady Flow Field in Low-Flow Turbine Operation

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OriginalspracheEnglisch
Aufsatznummer101003
Seitenumfang11
FachzeitschriftJournal of turbomachinery
Jahrgang146
Ausgabenummer10
Frühes Online-Datum23 Apr. 2024
PublikationsstatusVeröffentlicht - Okt. 2024

Abstract

Current operational considerations require steam turbines to operate in a more flexible way, with more frequent and faster start-up and an increasing part-load operation. For very low mass flowrates, the interaction of highly separated flow with the high-speed rotor blades causes windage flow. This type of flow is characterized by increased temperature and highly unsteady flow, which forms vortex structures that rotate at a fraction of the rotor speed. If their magnitude is sufficiently high and the frequency is close to the blade eigenfrequency, non-synchronous vibration (NSV) can be induced. In this paper, low-flow turbine operation is investigated using a three-stage turbine rig that features an instrumentation concept focused on capturing aerodynamic and aeroelastic phenomena. Extensive steady probe, unsteady pressure, and tip-timing measurements are utilized. The experimental scope covers a wide range of operating points in terms of rotational speed and mass flowrates. Low-flow regimes are detected by a reversal in torque and increase in temperature. Unsteady measurements during transient operation identified large-scale vortical flow structures rotating along the circumference, so-called rotating instabilities (RIs). The onset, growth, and breakdown regimes of RI are characterized for different low-flow conditions. The quantitative characteristics of RI with regard to nodal diameter and rotational speed are derived by a cross-correlation of multiple unsteady sensors. The blade vibration measurements show a moderate structural response from unsteady aerodynamic excitation, indicating no significant NSV occurring in the present experimental setup. Later in the study, an acoustic excitation system has been applied to trigger a locked-in NSV without interrupting the coherent flow structures. From that, significant blade response has been observed, revealing a high degree of mistuning and damping of the rotor blading.

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Characterizing the Unsteady Flow Field in Low-Flow Turbine Operation. / Kim, Hye Rim; Stania, Lennart; Maroldt, Niklas et al.
in: Journal of turbomachinery, Jahrgang 146, Nr. 10, 101003, 10.2024.

Publikation: Beitrag in FachzeitschriftArtikelForschungPeer-Review

Kim HR, Stania L, Maroldt N, Oettinger M, Seume JR. Characterizing the Unsteady Flow Field in Low-Flow Turbine Operation. Journal of turbomachinery. 2024 Okt;146(10):101003. Epub 2024 Apr 23. doi: 10.1115/1.4065243
Kim, Hye Rim ; Stania, Lennart ; Maroldt, Niklas et al. / Characterizing the Unsteady Flow Field in Low-Flow Turbine Operation. in: Journal of turbomachinery. 2024 ; Jahrgang 146, Nr. 10.
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AU - Kim, Hye Rim

AU - Stania, Lennart

AU - Maroldt, Niklas

AU - Oettinger, Marcel

AU - Seume, Joerg R.

N1 - Publisher Copyright: Copyright © 2024 by ASME.

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