CFD Modelling of Steam Turbine Last Stage Blades at Low Load Using Multiple Mixing Plane Approach

2021 ◽  
Author(s):  
Antonio Mambro ◽  
Francesco Congiu ◽  
Enzo Galloni
Keyword(s):  
Steam Turbine ◽  
Cfd Modelling ◽  
Multiple Mixing ◽  
Low Load ◽  
Last Stage

CFD Modelling of Steam Turbine Last Stage Blades at Low Load Using Multiple Mixing Plane Approach

2020 ◽  
Author(s):  
Antonio Mambro ◽  
Francesco Congiu ◽  
Enzo Galloni
Keyword(s):  
Steam Turbine ◽  
Flow Behavior ◽  
Volume Flow ◽  
Operating Conditions ◽  
Continuous Increase ◽  
Multiple Mixing ◽  
Wide Range ◽  
Low Load ◽  
Last Stage ◽  
Low Volume

Abstract The continuous increase of variable renewable energy and fuel cost requires steam turbine power plants to operate with high flexibility. This situation leads to steam turbines running at very low volume flow (LVF) for an extended time. Ventilation power and temperature predictions have a significant impact on the thermo-economic optimization of the power plant and lifetime assessment of the ventilating stages. In the last decade with increasing capabilities of CFD and computational resources, significant steps have been made in assessing complex flow behavior. Full size or scaled experimental testing of different last stage blades for a wide range of low load operating conditions is expensive, therefore CFD provides new opportunities in low load assessment. However, prediction of the flow structure of the ventilating stages still represents a challenge for the current CFD tools in terms of calculation time and reliability of the results. There are many different approaches in assessing this phenomenon, which require different computer resources and may not be necessary for most industrial applications. This paper presents the validation of the multiple mixing plane approach (MMP) presented by [9] for low-pressure steam turbine running at low load. Through a comparison with measurements results and more sophisticated methods, it is shown that this approach is able to sufficiently accurately predict the flow field and hence the ventilation power and temperature at low volume flow.

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.

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.

Aeromechanical Characterization of a Last Stage Steam Blade at Low Load Operation: Part 2 — Computational Modelling and Comparison

2020 ◽  
Author(s):  
Lorenzo Pinelli ◽  
Federico Vanti ◽  
Lorenzo Peruzzi ◽  
Andrea Arnone ◽  
Andrea Bessone ◽  
...  
Keyword(s):  
Steam Turbine ◽  
Power Plants ◽  
Computational Modelling ◽  
Test Facility ◽  
Nonlinear Phenomena ◽  
Aerodynamic Damping ◽  
Low Load ◽  
Non Linear ◽  
Last Stage ◽  
Load Conditions

Abstract This paper is part of a two-part publication that aims to experimentally and numerically evaluate the aerodynamic and mechanical damping of a last stage ST blade at low load operation. A three-stage downscaled steam turbine with a snubbered last stage moving blade LSMB has been tested in the T10MW test facility of Doosan Skoda Power R&D Department in the context of the FLEXTURBINE European project (Flexible Fossil Power Plants for the Future Energy Market through new and advanced Turbine Technologies). Aerodynamic and flutter simulations of different low load conditions have been performed. The acquired data are used to validate the unsteady CFD approach for the prediction of the aerodynamic damping in terms of logarithmic decrement. Numerical results have been achieved through an upgraded version of the URANS CFD solver, selecting appropriate and robust numerical setups for the simulation of very low load conditions, such as increased condenser pressure at the exhaust hood outlet. The numerical methods for blade aerodamping estimation are based on the computation of the unsteady pressure response caused by the row vibration. They are usually classified in time-linearized, harmonic balance and non-linear approaches both in frequency and time domain. The validation of all these methods historically started in the field of aeronautical low-pressure turbines and has been gradually extended to compressor blades and steam turbine rows. For the analysis of a steam turbine last rotor blade operating at strong part load conditions, non-linear methods are recommended as these approaches are able to deal with strong nonlinear phenomena such as shock waves and massive flow separations inside the domain. Experimental data have been used to separate the contributions of mechanical and aerodynamic damping, extrapolating to zero mass flow the total measured damping. Finally, the comparisons between the aerodynamic damping coming from measurements and CFD results have been reported in order to highlight the capability to properly predict the last stage blade flutter stability at low load conditions. Such comparisons confirms the flutter free design of the new snubbered LSMB blade.

scholarly journals EXPERIMENTAL AND NUMERICAL ASSESSMENT OF A LAST STAGE ST BLADE DAMPING AT LOW LOAD OPERATION

2018 ◽  
Vol 20 ◽  
pp. 16-28
Author(s):  
Andrea Bessone ◽  
Luigi Carassale ◽  
Roberto Guida ◽  
Zdeněk Kubín ◽  
Antonio Alfio Lo Balbo ◽  
...  
Keyword(s):  
Experimental Data ◽  
Numerical Analysis ◽  
Steam Turbine ◽  
Software Tool ◽  
Test Plant ◽  
Steam Turbines ◽  
Aerodynamic Damping ◽  
Numerical Assessment ◽  
Low Load ◽  
Last Stage

As LP steam turbines are requested to work at strong part-loads, LSB stalled and unstalled flutter may occur. Testing on a downscaled steam turbine in T10MW test plant have been carried out to measure LSB aggregated damping at low load. Also numerical analysis to predict aerodynamic damping have been performed and results have been compared to experimental data, allowing software tool validation at low load.

Aerodynamic and Structural Numerical Investigation of Full Annulus Last Stage of Steam Turbine Under Low Load Conditions

2020 ◽  
Author(s):  
Di Qi ◽  
Yifeng Chen ◽  
Gang Lin ◽  
Wenfu Li ◽  
Wei Tan
Keyword(s):  
Structural Analysis ◽  
Steam Turbine ◽  
Computational Cost ◽  
Coupled Analysis ◽  
Aerodynamic Loading ◽  
Unsteady Aerodynamic ◽  
Low Load ◽  
Blade Vibrations ◽  
Last Stage ◽  
Load Conditions

Abstract Operating at low load conditions may cause strong and non-synchronous unsteadiness and a high blade dynamic loading for the last stage blades (LSB). Full annulus models should be used to investigate the circumferential asymmetric flow unsteadiness and blade vibrations. Currently, although full annulus models have been applied to numerical aerodynamic studies, to authors’ knowledge, there is still no research including the full annulus in structural analysis due to the high computational cost. In this paper, an unsteady aerodynamic and structural coupled analysis method for an industrial steam turbine LSB using full annulus model under low load conditions is presented. To conduct finite element method (FEM) with limited computational resources, a new structural analysis procedure is proposed to calculate the dynamic stress. The aerodynamic analysis is conducted in both steady and unsteady computational fluid dynamics (CFD) calculations. The tip pressure ratio in the steady state calculations is used to predict the aerodynamic loading intensity. The unsteady results indicate typical flow characteristics under low load conditions, which show a big separation region behind the last rotor and tip vortex between last stator and rotor. Unsteady aerodynamic loading is mapped onto the blade surface as the excitation force. The structural analysis is performed to investigate the characteristics of blade vibrations and stress distributions of the full annulus LSB. Repeating the method, a reasonable characteristics curve of vibration stress against flow rates for LSB is calculated.

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.

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