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  • 2019 Volume 39 Issue 5
    Published: 15 May 2019
      
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  • Design Method for Fillet-like End Walls
    ZHANG Xuyang
    2019, 39(5): 345-352.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Based on simulation results of the simplified leading-edge model for turbine blades, a new model was developed for the fillet-like end wall by analyzing the flow and heat transfer characteristics of the end wall in the original model, and subsequently the flow and heat transfer behaviors were comparatively studied among the new end wall model, the end wall model with leading-edge fillet and the original model. Results show that the use of fillet-like end wall would make the static pressure distribution more uniform; the low energy fluid in the leading edge stagnation zone would flow toward the mainstream under the guidance of end wall pressure, and the strength of the horseshoe vortex would drop accordingly. Compared with the model with leading-edge fillet, the use of the new end wall model could eliminate the discontinuous line of the curvature between the end wall and the fillet, lead the accumulative low energy fluid out of the corner region, inhibit the generation of high strength corner vortex and decrease the heat transfer on the leading edge.
  • Research on Fluid-induced Vibration Characteristics of the Control Stage with Eccentric Tip Clearances Under Partial Admission Conditions
    ZHANG Yao, ZHANG Wanfu, GU Qianlei, CHEN Luqi, MA Kai, LI Chun
    2019, 39(5): 353-359.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Based on the computational fluid dynamics, three-dimensional models were established for the control stage of a 350 MW steam turbine to study the influence of rotor eccentricity and tip shroud on the characteristics of fluid-induced vibration under partial admission conditions with the valves being opened in different combinations and degrees. Calculated results show that with the rise of valve pressure, the accumulative mass flow increases while the fluid-induced force increases firstly and then decreases. The force mainly generates from the inner arc of the rotor blade. However, for the free blades in eccentric state, the force mainly comes from the top of the blade when the accumulative flow rate is relatively small. The fluid-induced force in vertical and horizontal direction is approximately equal in magnitude. Non-diagonal admissions produce larger fluid-induced force, which reaches the maximum for the model with shroud when valves I, Ⅱ and Ⅲ are open, and for the model without shroud when all the four valves are non-uniformly opened, sharing 24% to 35% weight of the high-pressure rotor. Both the rotor eccentricity and tip shroud increase the fluid-induced force, but the force is also affected by the partial admission mode, the eccentric direction and the relative position between the two factors. Under same working conditions, the maximum fluid-induced force in eccentric state is about 133.94% of that in un-eccentric state, and the maximum fluid-induced force for the model with shroud is about 150% of that without shroud.
  • Analysis and Optimization on the Structural Strength of a Main Steam Valve During Rapid Cold Startup at Fixed Parameters
    CHEN Shikun, WANG Peng, CAI Zhenwei, HONG Hui, WANG Weizhe
    2019, 39(5): 360-365.
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    A study was conducted on the structural strength of the main steam valve in a back-pressure turbine unit with manifold piping system during rapid cold startup at fixed parameters. A three-dimensional finite element model was established for the main steam valve using ABAQUS, so as to obtain its instantaneous temperature field and stress field in startup process, compare the calculated and measured temperatures at measuring points, and to analyze the effects of valve opening on the stress alteration. Results show that the calculated temperatures at measuring points of the main steam valve agree well with actual measurements. Obvious stress alteration exists in the main valve seat during startup of the main steam valve, which could be eliminated by changing the valve opening, thus to reduce the fatigue damage of the main valve seat.
  • Feature Extraction of Acoustic Emission Signals Under Hydraulic Turbine Cavitation Conditions Based on Improved EMD and Correlation Dimension
    LIU Zhong, YUAN Xiang, ZOU Shuyun, ZHOU Yungui, CHEN Ying
    2019, 39(5): 366-372.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To investigate the characteristics and evolution law of acoustic emission signals, a feature extraction method was proposed for the acoustic emission signals under hydraulic turbine cavitation conditions based on improved Empirical Mode Decomposition (EMD) and correlation dimension. The method of mirror extension combined with variable cosine window function was used to improve the conventional EMD, and the improved EMD was then applied to analyze the acoustic emission signals under cavitation conditions of a Francis hydraulic turbine. The time delay parameters and the best embedding dimensions for each order of intrinsic mode function (IMF) component of the acoustic emission signals were subsequently calculated respectively by autocorrelation method and pseudo-nearest-neighbor analysis algorithm, while the correlation dimensions of each order IMF were extracted using G-P algorithm, so as to study the change rules of the correlation dimension with the cavitation coefficient of the Francis turbine. Results show that with the cavitation state changing from non-cavitation to incipient cavitation and further to critical cavitation, the correlation dimension of each order of IMF components gradually increases, which directly reflects the cavitation evolution of the hydraulic turbine growing out of nothing from weak to strong, where the flow state becomes more turbulent.
  • Lubrication State Diagnosis of Journal Bearings Based on Information Exergy Closeness Degree of Acoustic Emission Signals
    LU Xuxiang, TAN Haoyu, CHEN Xiangmin, JIANG Yadi, RAO Hongde
    2019, 39(5): 373-379.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To effectively detect the lubrication states of journal bearings and improve the discrimination degree and accuracy of the state-based lubrication diagnosis, a diagnosis method was proposed for the lubrication state of journal bearings based on the process information exergy. Acoustic emission signals of the dry, semi-dry and liquid friction state of a journal bearing were collected in the simulated rotor test rig of a 300 MW turbo-generator set, and the acoustic emission signals were subsequently analyzed using the method of information exergy closeness degree and information exergy variance to achieve effective discrimination of different lubrication states. Results show that the method based on the change of information closeness and variance of acoustic emission signals can help to accurately diagnose the lubrication in different states, with higher information utilization rate and discrimination degree than those of the diagnosis method based on the information entropy band.
  • Research on Optimization of Flow Field and Concentration Field in a Double Variable Cross-section SCR Denitrification System
    WANG Zhaoyang, CHEN Hongwei, CHENG Kai, WANG Guangtao, LIU Xiaodong
    2019, 39(5): 380-386.
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    To reduce the large deviation factor of the velocity field and concentration field corresponding to the first-layer catalyst in the denitrification system of a 1 000 MW tower boiler, a three-dimensional model was established for the selective catalytic reduction (SCR) denitrification system, and subsequently the effects of deflector layout on the flow field in the double-variable cross-section flue were studied using numerical simulation. By comparing the simulation results of different deflector schemes, the flue structure was modified, with an optimal arrangement of deflectors obtained and a reasonable size of ammonia injection grid (AIG) determined. Results show that the concentration deviation factor of NH3 in the first-layer catalyst could be reduced to 2.32% by regional ammonia spraying, which ensures the uniform distribution of reactants in each channel of the catalyst and improves denitrification efficiency.
  • Multi-model NOx Emission Prediction Based on IGASA-FCM and IPSO-SVM for Coal-fired Power Plants
    FU Zhongguang, GAO Xuewei, LI Chuang, LIU Binghan, WANG Shucheng
    2019, 39(5): 387-393.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A novel multi-model modeling method was proposed for the SCR denitrification system by mining massive historical data of the system. Through theoretical and practical analysis of SCR denitrification systems, the training data set was divided to obtain the optimal clustering results using fuzzy C-means clustering (FCM) based on improved genetic algorithm simulated annealing (IGASA). Then corresponding sub-models were established by support vector machine (SVM), and the sub-model parameters were subsequently optimized based on improved particle swarm optimization (IPSO). Finally, an integral prediction model was built up by weighted fusion of the sub-model membership values. Taking the denitrification system of a power plant boiler as an example, the model was verified and then compared with that built by other modeling methods. Results show that the model proposed has strong generalization ability and high prediction accuracy.
  • Numerical Simulation of Biomass Fast Pyrolysis Based on Euler-Euler Multiphase Flow Model
    XUE Lianjin, LI Xinbao, WANG Yucheng, SHEN Pengfei
    2019, 39(5): 394-401.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    Based on Euler-Euler method, the kinetic model for single-step multi-component reaction was used to study the fast pyrolysis of biomass in a two-dimensional bubbling fluidized bed reactor, with focus on analysis of the particle flow, heat transfer, and the distribution of pyrolysis products in the reactor. Results show that the bubble flow benefits the mixing and heat exchange of gas, quartz sand and biomass particles. Through convective heat transfer with gas and contact heat conduction with quartz sand, the temperature of biomass rises rapidly, following which, fast pyrolysis of biomass occurs, with a pyrolysis temperature lying in 750-850 K, and the calculated yields of bio-oil, char, and non-condensable gas being 59.2%, 14.4% and 22.1%, respectively.
  • Research on Heave Motion Inhibition for the Semi-submersible Platform of Floating Wind Turbines with New Heave Plates
    HUANG Zhiqian, DING Qinwei, LI Chun
    2019, 39(5): 402-408.
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    A new type of semi-submersible platform equipped with a heave plate capable of effectively suppressing the heave motion was designed for floating wind turbines, while its dynamic response to the combined action of wind, wave and flow load was analyzed, which was subsequently compared with that of the three-buoy three-pillar semi-submersible platform. Results show that in the frequency-domain analysis, the heave plate has best suppression effect on the heave motion, followed by the pitch and sway motion; the radiation damping of original platform is closer to that of the heave plate platform in the sway, pitch and heave direction, but the additional mass of the latter is relatively large. In the time-domain analysis, compared with original platform, all the motion responses of heave plate platform are relatively small in the sway, pitch and sway direction, with best suppression effect on the heave motion, followed by the pitch and sway motion.
  • A Compound Control Method for Active Load Alleviation of a Smart Blade Wind Turbine Based on x-LMS
    ZHANG Wenguang, WANG Yifeng, LIU Haipeng, LIU Ruijie
    2019, 39(5): 409-417.
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    To study the control method for active load alleviation of large-scale wind turbines, taking the NREL 5 MW reference wind turbine as a research object, an unsteady aerodynamic model was established for the smart blade wind turbine with trailing edge flaps (TEFs), while its unsteady aerodynamic characteristics were analyzed. The pitch angle and TEF angle were controlled respectively based on x-LMS, and a compound control method of active load alleviation was proposed by combining the individual pitch control and TEF control, of which, the control effects were subsequently analyzed under different wind conditions. Results show that the model established can effectively simulate the unsteady aerodynamic characteristics of the smart blade wind turbine. The control method proposed can mitigate the fluctuation of high-frequency and low-frequency flapwise root moment and can significantly reduce the fatigue load of blades, thus achieving safety operation of the wind turbine.
  • Cold-end Optimization of a Coal-fired Power Generation System Integrated with a Supercritical CO2 Cycle
    ZHANG Qiang, XU Cheng, GAO Yachi, XU Gang, LIU Tong, YANG Yongping
    2019, 39(5): 418-424.
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    To reduce the high degree of superheat of the steam bleed and the large heat-transfer temperature difference to achieve high power generation efficiency of ultra supercritical coal-fired power units, an improved conceptual supercritical coal-fired power generation design was proposed, which integrates a supercritical CO2 (S-CO2) power cycle to utilize the superheat of steam bleeds to heat the CO2 medium and drive the CO2 cycle, thus reducing the degree of superheat significantly; whereas the air preheating process in boiler tail flue is divided into two stages, between which a low temperature economizer is allocated to heat the high-temperature feedwater and condensate. The energy-saving effects of the proposed system were analyzed based on a typical 1 000 MW supercritical power unit. Results show that, compared with the reference power unit and a conventional flue gas waste heat recovery system, the additional electric power output of the proposed system has been increased by 30.07 MW and 25.51 MW, respectively. Moreover, the power supply coal consumption has been reduced by 7.9 g/(kW·h) and 6.7 g/(kW·h), respectively, indicating significant energy-saving effects.
  • Creep Rupture Life Prediction of T/P91 Heat-resistant Steels Based on Ω Method
    WANG Zheng, WANG Yanfeng, WAN Haibo
    2019, 39(5): 425-432.
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    The creep rupture life of T/P91 heat-resistant steels respectively in original and service state was predicted by Ω method, and the results were compared with those obtained by isotherm method and Larson-Miller parameter method. Meanwhile, an accelerated test scheme was proposed based on Ω method, which could rapidly predict the creep rupture life with only one specimen under given temperatures and stress parameters. Results show that compared with isotherm method and Larson-Miller parameter method, the accelerated Ω method shows higher prediction accuracy. For service state T/P91 heat-resistant steels, nearly same Ω values shall be obtained in different acceleration schemes, and the predicted values of creep fracture time would be in good agreement with actual measurements.