Effects of Upstream Sprayed Water on Steam Flow Conditions and Blade Vibrations of a Low Pressure Steam Turbine

2016 ◽  
Author(s):  
Naoki Shibukawa ◽  
Yoshihiro Ishikawa ◽  
Yoshifumi Iwasaki ◽  
Kota Chiba
Keyword(s):  
Steam Turbine ◽  
Low Pressure ◽  
Steam Flow ◽  
Flow Conditions ◽  
Large Size ◽  
Low Load ◽  
Vibration Stress ◽  
Experimental Works ◽  
Last Stage ◽  
Two Stages

A shutdown operation of a large size steam turbine could possibly cause flashing phenomena of the pooled drain water in low-pressure heaters. The boiled steam is sometimes in the same amount as the main flow in the case where shutdown is executed during low load conditions, and returns to the steam flow path through the extraction lines. A series of experimental works with a subscale model turbine facility has been carried out to investigate the vibration stress behavior, and the steady and unsteady pressures under the flashing back conditions. It was observed that the blades of the two stages before the last stage (L-2) and a stage before the last stage (L-1) endured their peak vibration stresses immediately after the flash-back flow reached the turbine. In the meantime, the vibration stresses of the last stage (L-0) blades were reduced. In this paper, the behavior of the water droplets and their vaporization in the steam path were mainly investigated. A series of experiment was conducted in which several amounts of controlled sprayed water were continuously supplied into the turbine. The transient steam condition and blade’s vibration stresses were measured at the same time. The results showed the possibility that sprayed water upstream can change the mass flow rate and temperature downstream to avoid the unstable steam flow and overheating of the long blades during low load operation.

An Experimental Investigation of the Influence of Flash-Back Flow on Last Three Stages of Low Pressure Steam Turbines

2014 ◽  
Author(s):  
Naoki Shibukawa ◽  
Yoshifumi Iwasaki ◽  
Yoshiaki Takada ◽  
Itaru Murakami ◽  
Takashi Suzuki ◽  
...  
Keyword(s):  
Reverse Flow ◽  
Flow Region ◽  
Low Pressure ◽  
Detailed Examination ◽  
Steam Turbines ◽  
Back Flow ◽  
Large Size ◽  
Vibration Stress ◽  
Last Stage ◽  
Two Stages

A shutdown operation of a large size steam turbine could possibly cause flashing phenomena of the pooled drain water in low-pressure heaters. The boiled steam is sometimes in the same amount as the main flow in the case where shutdown is executed during low load conditions, and returns to the steam flow path through the extraction lines. A series of experimental work with a subscale model turbine facility has been carried out to investigate the vibration stress behavior, and the steady and unsteady pressures under the flashing back conditions. It was observed that the blades of the two stages before the last stage (L-2) and a stage before the last stage (L-1) presented their peak vibration stresses immediately after the flash-back flow reached the turbine. In the meantime, the vibration stresses of the last stage (L-0) blades were reduced for a few tens of seconds. It can be thought that the flash-back flow pushed out the reverse flow region around the L-0 blades and allow the blades to be more stable. A detailed examination with measured data of the L-2 blade explained that, as long as the flash-back flow has small wetness, the blade is excited in its specific vibration modes in larger than 8th harmonic of rotational speed, but once the flash back flow carries water droplets, the fluid force in random frequencies remarkably increases and excites the blade in less than 7th harmonic range.

An Experimental Investigation of the Influence of Flash-Back Flow on Last Three Stages of Low Pressure Steam Turbines

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Naoki Shibukawa ◽  
Takao Fukushima ◽  
Yoshifumi Iwasaki ◽  
Yoshiaki Takada ◽  
Itaru Murakami ◽  
...  
Keyword(s):  
Reverse Flow ◽  
Flow Region ◽  
Low Pressure ◽  
Detailed Examination ◽  
Steam Turbines ◽  
Back Flow ◽  
Large Size ◽  
Vibration Stress ◽  
Last Stage ◽  
Two Stages

A shutdown operation of a large size steam turbine could possibly cause flashing phenomena of the pooled drain water in low-pressure heaters. The boiled steam is sometimes in the same amount as the main flow in the case where shutdown is executed during low load conditions, and returns to the steam flow path through the extraction lines. A series of experimental work with a subscale model turbine facility has been carried out to investigate the vibration stress behavior, and the steady and unsteady pressures under the flashing back (FB) conditions. It was observed that the blades of the two stages before the last stage (L-2) and a stage before the last stage (L-1) presented their peak vibration stresses immediately after the flash-back flow reached the turbine. In the meantime, the vibration stresses of the last stage (L-0) blades were reduced for a few tens of seconds. It can be thought that the flash-back flow pushed out the reverse flow region around the L-0 blades and allow the blades to be more stable. A detailed examination with measured data of the L-2 blade explained that, as long as the flash-back flow has small wetness, the blade is excited in its specific vibration modes in larger than eighth harmonic of rotational speed, but once the flash-back flow carries water droplets, the fluid force in random frequencies remarkably increases and excites the blade in less than seventh harmonic range.

scholarly journals Research on Water Droplet Movement Characteristics in the Last Two Stages of Low-Pressure Cylinder of Steam Turbine Under Low Load Conditions

2021 ◽  
Vol 9 ◽  
Author(s):  
Shuangshuang Fan ◽  
Ying Wang ◽  
Kun Yao ◽  
Yi Fan ◽  
Jie Wan ◽  
...  
Keyword(s):  
Steam Turbine ◽  
Turbine Blades ◽  
Low Pressure ◽  
Water Droplets ◽  
Movement Characteristics ◽  
Low Load ◽  
Pressure Cylinder ◽  
Last Stage ◽  
Two Stages ◽  
Load Conditions

In the operating process of the coal-fired generation during flexible peaking regulation, the primary and secondary water droplets in the steam flowing through the last two stages of the low-pressure cylinder could influence the efficiency and safety of the steam turbine definitely. However, systematic analysis of the movement characteristics of water droplets under low-load conditions is scarcely in the existing research, especially the ultra-low load conditions below 30%. Toward this end, the more novel algebraic slip model and particle transport model mentioned in this paper are used to simulate the primary and secondary water droplets. Taking a 600 MW unit as a research object, the droplets motion characteristics of the last two stages were simulated within four load conditions, including 100, 50, 40, and 30% THA. The results show that the diameter of the primary water droplets is smaller, ranging from 0 to 1 µm, during the flexible peak regulation process of the steam turbine. The deposition is mainly located at the entire moving blades and the trailing edge of the last two stator blades. With the load decreasing, the deposition effect decreases sustainably. And the larger diameters of secondary water droplets range from 10 to 300 µm. The erosion of secondary water droplets in the last stage is more serious than that of the second last stage for different load conditions, and the erosion of the second last stage could be negligible. The pressure face and suction face at 30% blade height of the last stage blade have been eroded most seriously. The lower the load, the worse erosion from the secondary water droplets, which poses a potential threat to the fracture of the last stage blades of the steam turbine. This study provides a certain reference value for the optimal design of steam turbine blades under flexible peak regulation.

Aerodynamic Numerical Investigation of Low-Pressure Steam Turbine Last Stage Under Low Load Conditions With Mode Decomposition Methods

2019 ◽  
Author(s):  
Ping Hu ◽  
Tong Lin ◽  
Rui Yang ◽  
Xiaocheng Zhu ◽  
Zhaohui Du
Keyword(s):  
Steam Turbine ◽  
Frequency Spectrum ◽  
Low Frequency ◽  
Low Pressure ◽  
Unsteady Pressure ◽  
Mode Decomposition ◽  
Low Load ◽  
Last Stage ◽  
Operating Points ◽  
Load Conditions

Abstract It is common that steam turbine works at different operating points, especially under low load conditions, to cater to complex and varied demands for power generation recently. Considering the long and thin shape of last stage moving blades (LSMBs) in a low-pressure (LP) steam turbine, there are many challenges to design a suitable case which balances global efficiency against sufficient structure strength when suffering excitations at low load operating points. In present work, the aim is to extract specific aerodynamic excitations and recognize their distribution and propagation features. Firstly, steady 3D computational fluid dynamics (CFD) calculations are simulated at 25GV and 17GV (25% and 17% of design mass flow conditions) and corresponding unsteady calculations are performed with enough rotor revolutions to obtain integrated flow periodicities. Unsteady pressure signals near tip region of LSMBs are monitored circumferentially in both static and rotating coordinates. The fast Fourier transformation (FFT) results of unsteady pressure signals show that there are broadband humps with small disturbance amplitudes in low frequency spectrum at 25GV, however, a sharp spike is shown in low frequency spectrum at 17GV. Further, circumferential mode decomposition (CMD) method has been applied to distinguish different fluctuations in frequency and the mode numbers and circumferential propagating pace of which have been obtained. Finally, dynamic mode decomposition (DMD) method has been performed to describe detailed mode shapes of featured flow perturbances both in static and rotating coordinate system. These analyses indicate that at 25GV, a band of unsteady responses with very low amplitude was noted which has some features similar to rotating instability (RI). However, distribution and propagation features of flow unsteadiness at 17GV are in good agreement with rotating stall (RS) in compressor.

Unsteady Flow Features and Vibration Stresses of an Actual Size Steam Turbine Last Stage in Various Low Load Conditions

2013 ◽  
Author(s):  
Naoki Shibukawa ◽  
Yoshifumi Iwasaki ◽  
Mitsunori Watanabe
Keyword(s):  
Steam Turbine ◽  
Pressure Fluctuation ◽  
Load Condition ◽  
Test Facility ◽  
Stress Increase ◽  
Unsteady Pressure ◽  
Low Load ◽  
Vibration Stress ◽  
Last Stage ◽  
Load Conditions

Experimental investigations with a six stage real scale low pressure steam turbine operated at a very low load conditions are presented in this paper. Although the tested 35 inch last stage blades are circumferentially coupled at both tip and mid span with an intention to reduce the vibration stress, still its increase was observed at extremely low load condition. The pressure fluctuations were measured by several silicon diaphragm sensors which were mounted on both inner and outer casings of the stator inlet, exit and blade exit position. The measurement of the vibration stress was performed by strain gauges on several blades. The power spectra of unsteady pressures were precisely investigated considering both their location and steam flow condition. And the results implied that huge reverse flow and re-circulation started in the same location as a blade-to-blade CFD predicted. In terms of the correlation between vibration stress and the flow feature, the pressure fluctuation around the blade tip produces dominant effects on the vibration stress. The unsteady pressure frequency were also investigated and compared with those of the blade resonance and rotational speed. Basic trends observed in the results are similar to what other researchers reported, and on top of that, the continuous trends of pressure fluctuation and blade vibration stress were systematically investigated. Even the wall pressure, not the pressure on blade surface, showed the effective fluctuations which excited the several nodes of natural frequencies of the last stage blade. A series of FFT of fluid force by a full annulus quasi-steady CFD simulation seems to predict dominant mode of the excitation which account for the behavior of vibration stresses. The mechanism of the rapid stress increase was examined by considering CFD results and measured unsteady pressure data together. As the test facility takes a responsibility as an independent power producer, the tests were conducted in real plant operations which include multi stage effects, inlet distortions, Reynolds Number effect and so on. The obtained data and the particular indicator of vibration stress increase can be used as a part of design tool validation with neither aerodynamic nor mechanical corrections.

On the Prediction and Theory of the Temperature Increase of Low Pressure Last Stage Moving Blades During Low Volume Flow Conditions, and Limiting it Through Steam Extraction Methods

2014 ◽  
Author(s):  
Adam Beevers ◽  
Said Havakechian ◽  
Benjamin Megerle
Keyword(s):  
Steam Turbine ◽  
Temperature Increase ◽  
Low Pressure ◽  
Volume Flow ◽  
Flow Conditions ◽  
Steam Extraction ◽  
Last Stage ◽  
Low Volume ◽  
Critical Regions ◽  
Ventilation Conditions

During extreme low volume flow conditions, the last stages of a low pressure steam turbine operate in ventilation conditions that can cause a significant temperature increase of critical regions of the last stage moving blade. Under some conditions, the blade temperature may rise above a safe operating temperature, requiring the machine to be shut down. Limiting the heating effect on the last stage moving blade increases the allowable operating range of the low pressure turbine. One common method is to spray water droplets into the low pressure exhaust. As the length of last stage moving blades continues to increase, this method reaches its limit of practical operating effectiveness due to the amount of water required and its impact on the erosion of the LSB. An investigation into complimentary solutions to limit the temperature increase was conducted using CFD. An appropriate CFD setup was chosen from a sensitivity study on the effect of geometry, mesh density, turbulence model and time dependency. The CFD results were verified against steam turbine data from a test facility. The proposed complimentary solutions to limit the temperature increase include low temperature steam extraction, targeted for critical regions of the moving blade. From the test turbine and CFD results, the drivers of the temperature increase during ventilation conditions are identified and described.

On the Prediction and Theory of the Temperature Increase of Low Pressure Last Stage Moving Blades During Low Volume Flow Conditions, and Limiting it Through Steam Extraction Methods

2015 ◽  
Vol 137 (10) ◽  
Author(s):  
Adam Beevers ◽  
Said Havakechian ◽  
Benjamin Megerle
Keyword(s):  
Steam Turbine ◽  
Temperature Increase ◽  
Low Pressure ◽  
Volume Flow ◽  
Flow Conditions ◽  
Steam Extraction ◽  
Last Stage ◽  
Low Volume ◽  
Critical Regions ◽  
Ventilation Conditions

During extreme low volume flow conditions, the last stages of a low pressure steam turbine operate in ventilation conditions that can cause a significant temperature increase of critical regions of the last stage moving blade (LSB). Under some conditions, the blade temperature may rise above a safe operating temperature, requiring the machine to be shut down. Limiting the heating effect on the LSB increases the allowable operating range of the low pressure turbine. One common method is to spray water droplets into the low pressure exhaust. As the length of LSBs continues to increase, this method reaches its limit of practical operating effectiveness due to the amount of water required and its impact on the erosion of the LSB. An investigation into complimentary solutions to limit the temperature increase was conducted using CFD. An appropriate CFD setup was chosen from a sensitivity study on the effects from geometry, mesh density, turbulence model, and time dependency. The CFD results were verified against steam turbine data from a scaled test facility. The proposed solutions include low temperature steam extraction, targeted for critical regions of the moving blade. From the test turbine and CFD results, the drivers of the temperature increase during ventilation conditions are identified and described.

scholarly journals Failure Analysis in Lacing Wire Of Last Stage Low Pressure Steam Turbine Blade

2021 ◽  
Vol 1096 (1) ◽  
pp. 012097
Author(s):  
A M Kongkong ◽  
H Setiawan ◽  
J Miftahul ◽  
A R Laksana ◽  
I Djunaedi ◽  
...  
Keyword(s):  
Failure Analysis ◽  
Steam Turbine ◽  
Turbine Blade ◽  
Low Pressure ◽  
Pressure Steam ◽  
Steam Turbine Blade ◽  
Last Stage

Some Experiments on Wet Steam Flow Visualization in Large Steam Turbine Blading

1976 ◽  
Vol 98 (3) ◽  
pp. 573-577 ◽  
Author(s):  
J. Krzyz˙anowski ◽  
B. Weigle
Keyword(s):  
Steam Turbine ◽  
Steam Flow ◽  
Light Sources ◽  
Phase Flow ◽  
Wet Steam ◽  
Experimental Conditions ◽  
Advantages And Disadvantages ◽  
Primary Droplet ◽  
Last Stage ◽  
Wet Steam Flow

In a series of experiments aimed at the visualization of the wet steam flow in the exhaust part of a 200 MW condensing steam turbine a set of periscopes and light sources was used. The aim of the experiment was: 1 – The investigation of the liquid-phase flow over the last stage stator blading of the turbine mentioned. 2 – The investigation of the gaseous-phase flow through the last stage blading at full and part load. The first part of the program partially failed due to the opaqueness of the wet steam atmosphere for the turbine load higher than 10–20 MW. The detailed experimental conditions will be described. An assessment of the primary droplet size will also be given. The preliminary results of the second part of the program will be outlined. The advantages and disadvantages of the equipment used will be discussed.

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