Unsteady Flow Effects on Steam Turbine Last Stage Blades at Very Low Load Operating Condition

Tanuma, Tadashi; Ogawa, Michio; Okuda, Hiroshi; Hashimoto, Gaku; Shibukawa, Naoki; Okuno, Kenichi; Tsukuda, Tomohiko

doi:10.1115/gt2018-76498

Cited by 8 publications

(8 citation statements)

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“…Further research by Sigg and Rice 12 showed that the system RI was influenced by the exhaust shape. Nonsynchronous unsteady aerodynamic excitations in the last stage were also found by Liu et al 13 and Tanuma et al 14 Besides the flow fluctuation, Beevers et al 15 and Mambro et al 16,17 found that in this region, due to lack of axial flow, heat was difficult to dissipate through convection, and the temperature of the flow increased abnormally, which caused the LSMB tip and the casing to be in high temperature.…”

Section: Introductionmentioning

confidence: 57%

Numerical investigation on flow instabilities in low-pressure steam turbine last stage under different low-load conditions

Lin²,

Yang³

et al. 2021

Proceedings of the Institution of Mechanical Engineers, Part A:

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The modern power generation system requires steam turbines operating at flexible operating points, and flow instabilities readily occur in the low-pressure (LP) last stage under low-load conditions, which may cause failure of the last stage moving blades. Some studies have shown that within this operating range, a shift of the operating point may lead to flow instabilities. Numerical simulation has gradually developed into a popular method for such researches, but it is expensive for a complex model, which has to be balanced between efficiency and accuracy. This work is divided into three parts: Firstly, one of the low-load conditions is selected to provide both URANS model and the Scale-Adaptive Simulation (SAS) model. The results of the two models are compared to evaluate specific flow phenomena; Secondly, through calculations of different low-load conditions, the flow structure and propagation characteristics of instabilities in the last stage are obtained; Finally, flow analysis is applied to explain the formation mechanism of flow instabilities in LP steam turbines. The results show that, the introduction of SAS model increases the randomness of flow over time, but does not fundamentally change the flow instabilities. Flow instabilities take different forms at different flow rate, from rotating instability to rotating stall. The formation of flow instabilities is related to the radial flow in the cascade passages.

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Section: Introductionmentioning

confidence: 57%

Numerical investigation on flow instabilities in low-pressure steam turbine last stage under different low-load conditions

Lin²,

Yang³

et al. 2021

Proceedings of the Institution of Mechanical Engineers, Part A:

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show abstract

“…In recent years, the occurrences of RI in steam turbines are frequently reported through tests or numerical simulations. 18–20…”

Section: Introductionmentioning

confidence: 99%

“…Although it has not been clearly proposed in researches of steam turbines, the characteristics of blade dynamic stress measurements in Refs. 18 and 26 showed that with the continuous change of operating parameters, the blade dynamic stress would maintain a relatively high level within a certain range after an abnormal rise. It seems to indicate that the abnormal vibrations of LP steam turbine LSMBs under low-load conditions are not only resonance, but more likely to be lock-in phenomenon within a certain frequency range.…”

Section: Introductionmentioning

confidence: 99%

“…In recent years, the occurrences of RI in steam turbines are frequently reported through tests or numerical simulations. [18][19][20] Until now, there is no public experimental description of the complete formation process of NSV in steam turbines, but some reference can be drawn from compressors. Holzinger et al 21 tested on a 1.5-stage transonic compressor configuration with large tip clearance and found that wall pressure transducers detected typical RI fluctuations before obvious blade vibrations occurred.…”

Section: Introductionmentioning

confidence: 99%

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Numerical investigations on non-synchronous vibration and frequency lock-in of low-pressure steam turbine last stage

Zhu

Lin³

et al. 2021

Proceedings of the Institution of Mechanical Engineers, Part A:

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The flow phenomenon of rotating instability (RI) and its induced non-synchronous vibrations (NSV) in the last stage have gradually become a security problem that restricts the long-term flexible operations of modern large-scaled low-pressure steam turbines. Especially, if one structural mode of the last stage moving blade (LSMB) is excited, significant blade vibrations may potentially lead to high-cycle fatigue failure. A loosely coupled computational fluid dynamics reduced model with prescribed blade vibrations has been established to investigate NSV of the LSMB and the potential lock-in phenomenon under low-load conditions. Firstly, calculations with reduced multi-passage domain have been verified by comparing with the results of the full-annulus one, and an appropriate reduced domain is determined. Secondly, a set of calculations by controlling blade vibration parameters indicate that lock-in phenomenon between RI frequency and blade vibration frequency may occur when nodal diameters of cascade vibrations is coincident with the wave number of RI. Furthermore, dynamic modal decomposition technology has been employed to identify the unsteady pressure field around the blade surface and to reveal the interaction relationship between the flow modes of RI and vibration-induced pressure disturbance. Finally, the blade response evaluation based on harmonic analysis shows that in NSV, the global maximum dynamic response level of locked-in case is nearly 20 times than that of unlocked one.

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“…The flow research in steam turbines at low regimes is performed mainly using numerical simulations of the flow [1,2]. In certain cases experimentally obtained results are available [3], when experiments were performed on model steam turbines. It is valuable to compare both methods, which ensures two-way data validation [4].…”

Section: Introductionmentioning

confidence: 99%

Experimental steam turbine T10MW cold end cooling by water spraying

Hoznedl

2021

MATEC Web Conf.

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The paper deals with steam flow in experimental turbine T10MW, located in Škoda laboratory. The flow was examined for low or negative outputs of the turbine, i.e. for the so called last stages ventilation. The flow path of the turbine was in the Boiler Feed Pump Turbine (BFPT) version. It had all together 4 stages out of which two were last stages with the outlet to the condenser. In the area of each of the two outlets cooling nozzles were located with water for cooling the outlet steam flow and the area of last blades root cross-sections. Cooling of these areas is necessary due to the compression heat that occurs in the off design (ventilation) regimes. Various proportional amounts of cooling water and flowing steam were tested experimentally in constant pressure behind both last stages. Due to the fact that the flow path and the exhaust hood were fitted with many static pressure taps, thermometers and with the possibility of probing the temperature field along the outlet cross-section height, a number of results were achieved. These were mainly the turbine outputs, steam flows through the blades and cooling nozzles, determination of saturation limits in individual places at the outlet as well as temperature differences measured by the probe and stable thermometers. It was found out that the amount of cooling water was oversized for blade roots cooling, while the flow at the tip was cooled only minimally. The results are beneficial both in terms of further research of steam turbines in low regimes because this is how most newly produced machines are operated and for the designers of these machines.

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Unsteady Flow Effects on Steam Turbine Last Stage Blades at Very Low Load Operating Condition

Cited by 8 publications

References 0 publications

Numerical investigation on flow instabilities in low-pressure steam turbine last stage under different low-load conditions

Numerical investigation on flow instabilities in low-pressure steam turbine last stage under different low-load conditions

Numerical investigations on non-synchronous vibration and frequency lock-in of low-pressure steam turbine last stage

Experimental steam turbine T10MW cold end cooling by water spraying

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