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.

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.

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.

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.

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.

scholarly journals Study on water erosion and preventive measures of last stage blade of steam turbine

2021 ◽  
Vol 2076 (1) ◽  
pp. 012071
Author(s):  
Zhengxian Wang ◽  
Tong Liu ◽  
Renda Luo
Keyword(s):  
Steam Turbine ◽  
Power Plants ◽  
Preventive Measures ◽  
Dynamic Performance ◽  
Thermal Power ◽  
Turbine Blades ◽  
Water Erosion ◽  
Low Load ◽  
New Energy ◽  
Last Stage

Abstract In the background of carbon peak and carbon neutralization, most thermal power plants are more involved in peak regulation and even in-depth peak regulation in order to absorb new energy such as wind power and Solar power. When the turbine is running under low load, the exhaust pressure decreases, which leads to the increase of exhaust humidity. More and more turbine blades have water erosion. The erosion of the last stage blades will worsen the dynamic performance of the turbine, increase the risk of the last stage blade fracture, and threaten the safe operation of the turbine. This paper studies the mechanism of the last stage blade erosion of steam turbine, and analyzes the main factors which influence the erosion with examples. Combined with the mechanism of water erosion, the relevant preventive measures are made for reference of power supply plant.

Development of Long Rotating Blade Applied in the New Generation Nuclear Steam Turbine

2012 ◽  
Author(s):  
Kai Cheng ◽  
Zeying Peng ◽  
Gongyi Wang ◽  
Xiaoming Wu ◽  
Deqi Yu
Keyword(s):  
Steam Turbine ◽  
Nuclear Power ◽  
Power Plants ◽  
Structure Design ◽  
Good Reliability ◽  
Pressurized Water ◽  
Height Range ◽  
Water Reactor ◽  
Rotating Blade ◽  
Last Stage

In order to meet the high economic requirement of the 3rd generation Pressurized Water Reactor (PWR) or Boiling Water Reactor (BWR) applied in currently developing nuclear power plants, a series of half-speed extra-long last stage rotating blades with 26 ∼ 30 m2 nominal exhaust annular area is proposed, which covers a blade-height range from 1600 mm to 1900 mm. It is well known that developing an extra long blade is a tough job involving some special coordinated sub-process. This paper is dedicated to describe the progress of creating a long rotating blade for a large scaled steam turbine involved in the 3rd generation nuclear power project. At first the strategy of how to determine the appropriate height for the last-stage-rotating-blade for the steam turbine is provided. Then the quasi-3D flow field quick design method for the last three stages in LP casing is discussed as well as the airfoil optimization method. Furthermore a sophisticated blade structure design and analyzing system for a long blade is introduced to obtain the detail dimension of the blade focusing on the good reliability during the service period. Thus, except for CAD and experiment process, the whole pre-design phase of the extra-long turbine blade is presented which is regarded as an assurance of the operation efficiency and reliability.

The Effect of Stage-Diffuser Interaction on the Aerodynamic Performance and Design of LP Steam Turbine Exhaust Systems

2018 ◽  
Author(s):  
Bowen Ding ◽  
Liping Xu ◽  
Jiandao Yang ◽  
Rui Yang ◽  
Yuejin Dai
Keyword(s):  
Steam Turbine ◽  
Renewable Energy Sources ◽  
Rotor Blades ◽  
Steam Turbines ◽  
Flow Conditions ◽  
Part Load ◽  
Last Stage ◽  
Load Conditions ◽  
Turbine Exhaust ◽  
Exhaust Systems

Modern large steam turbines for power generation are required to operate much more flexibly than ever before, due to the increasing use of intermittent renewable energy sources such as solar and wind. This has posed great challenges to the design of LP steam turbine exhaust systems, which are critical to recovering the leaving energy that is otherwise lost. In previous studies, the design had been focused on the exhaust diffuser with or without the collector. Although the interaction between the last stage and the exhaust hood has been identified for a long time, little attention has been paid to the last stage blading in the exhaust system’s design process, when the machine frequently operates at part-load conditions. This study focuses on the design of LP exhaust systems considering both the last stage and the exhaust diffuser, over a wide operating range. A 1/10th scale air test rig was built to validate the CFD tool for flow conditions representative of an actual machine at part-load conditions, characterised by highly swirling flows entering the diffuser. A numerical parametric study was performed to investigate the effect of both the diffuser geometry variation and restaggering the last stage rotor blades. Restaggering the rotor blades was found to be an effective way to control the level of leaving energy, as well as the flow conditions at the diffuser inlet, which influence the diffuser’s capability to recover the leaving energy. The benefits from diffuser resizing and rotor blade restaggering were shown to be relatively independent of each other, which suggests the two components can be designed separately. Last, the potentials of performance improvement by considering both the last stage rotor restaggering and the diffuser resizing were demonstrated by an exemplary design, which predicted an increase in the last stage power output of at least 1.5% for a typical 1000MW plant that mostly operates at part-load conditions.

A Novel Method of Coupling the Steam Turbine Exhaust Hood and the Last Stage Blades Using the Non-Linear Harmonic Method

2013 ◽  
Author(s):  
Zoe Burton ◽  
Grant Ingram ◽  
Simon Hogg
Keyword(s):  
Steam Turbine ◽  
Turbine Blades ◽  
Computation Time ◽  
Computational Effort ◽  
Alternative Methods ◽  
Test Case ◽  
Exhaust Hood ◽  
Harmonic Method ◽  
Non Linear ◽  
Last Stage

The exhaust hood of a steam turbine is a vital area of turbomachinery research its performance strongly influences the power output of the last stage blades. It is well known that accurate CFD simulations are only achieved when the last stage blades are coupled to the exhaust hood to capture the strong interaction. This however presents challenges as the calculation size grows rapidly when the full annulus is calculated. The size of the simulation means researchers are constantly searching of methods to reduce the computational effort without compromising solution accuracy. This work uses a novel approach, by coupling the last stage blades and exhaust hood by the Non-Linear Harmonic Method, a technique widely used to reduce calculation size in high pressure turbine blades and axial compressors. This has been benchmarked against the widely adopted Mixing Plane method. The test case used is the Generic Geometry, a representative exhaust hood and last stage blade geometry that is free from confidentiality and IP restrictions and for which first calculations were presented at last year’s conference [1]. The results show that the non-uniform exhaust hood inlet flow can be captured using the non-liner harmonic method, an effect not previously achievable with single passage coupled calculations such as the mixing plane approach. This offers a significant computational saving, estimated to be a quarter of the computation time compared with alternative methods of capturing the asymmetry with full annulus frozen rotor calculations.

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