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  • 2018 Volume 38 Issue 2
    Published: 15 February 2018
      
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  • Prediction of Steam Turbine Heat Rate Based on Sine Cosine Algorithm
    NIU Peifeng, WU Zhiliang, MA Yunpeng, SHI Chunjian, LI Jinbai
    2018, 38(2): 85-91.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To accurately predict the heat rate of steam turbines, an integrated modeling method was proposed by combining an improved adaptive sine consine algorithm (ASCA) based on Bloch coordinates of qubits with the fast learning network (FLN). The specific way is to compare the ASCA with classical artificial bee colony (ABC) algorithm, teaching-learning-based optimization (TLBO) algorithm and sine consine algorithm (SCA), and then to set up a prediction model for the heat rate using the operation data collected from a 600 MW supercritical steam turbine unit, and finally to contrast the prediction results among the ASCA-FLN, FLN, ABC-FLN, TLBO-FLN and SCA-FLN model. Results show that the ASCA-FLN prediction model has higher prediction accuracy and stronger generalization ability, which therefore can be used to predict the heat rate of steam turbines more accurately.
  • Simulation Study of the Trailing Edge Slot Ejection on a Transonic Turbine Cascade
    YAO Shichuan, CHEN Liu, XUAN Liming, SHI Liuliu, DAI Ren
    2018, 38(2): 92-97.
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    Spalart-Allmaras (S-A) turbulence model was used to simulate and analyze the steady flow structure of trailing edge slot ejection on a transonic turbine cascade, while a study was conducted on the effects of different pressure ratios of trailing edge ejection on following parameters, such as the structure and intensity of shock, the structure of wake and various energy losses, etc. Results show that the wake width, the lowest velocity magnitude, and the intensity of trailing edge shock can all be reduced by slot ejection, which has relatively larger weakening effect on the shock at pressure side. The ejection causes the formation position of shock to approach the trailing edge, leading to the increase of the shock angle. Total kinetic energy loss of the cascade can be reduced by ejection. The shock loss and wake loss are more sensitive to the ejection pressure ratio than the loss in boundary layer. According to the state of cascade exit, there exists an optimum ejection pressure ratio in the transonic turbine.
  • Modeling and Dynamic Simulation of H-class Heavy-duty Gas Turbines
    REN Jingqi, CAO Yue, SANG Yiqian, QIAO Hong, DAI Yiping, WANG Yongqing
    2018, 38(2): 98-104.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    A nonlinear dynamic simulation model was built for the H-class heavy-duty gas turbine using object-oriented modularized technique. To improve the simulation accuracy, the effects of different gas compositions and specific heat capacities on the accuracy of the model were considered. Through simulations on the Simulink platform, the dynamic characteristics of H-class heavy-duty gas turbines were studied under external disturbances and different moments of inertia on the rotor. Results show that under rated conditions, the larger the load distrubance is, the greater the over adjustment of rotational speed and fuel mass flow will be, but the adjustment time in different load disturbance processes is nearly the same. When the ambient temperature increases, the rotational speed first increases and then declines while the fuel mass flow first declines and then increases; the exhaust gas flow decreases and the exhaust temperature increases slightly during steady state operation of the turbine. In the process of gas turbine load rejection, the smaller the moment of inertia on rotor is, the greater the over adjustment of rotational speed/fuel mass flow and the shorter adjustment time will be; whereas, the greater the moment of inertial on rotor is, the stronger robustness will be resulted against load disturbance. There exists an optimum scheme of gas turbine shaft arrangement; when the single shaft arrangement with 3S clutch is adopted, the dynamic performance of gas turbine would be relatively good and the stability of the system would be relatively high.
  • Influence of Hole Spacing on the Film Cooling Effectiveness of a Gas Turbine Moving Blade
    TANG Xuezhi, LI Luping, HUANG Zhangjun, LIANG Yongchun, ZHONG Wanli
    2018, 38(2): 105-113.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To improve the cooling effectiveness of a gas turbine moving blade, three-dimensional constant incompressible N-S equations were dispersed based on Realizable k-ε turbulence model combined with Simple algorithm and finite volume method, so as to analyze the influence of hole spacing on the film cooling effectiveness of the moving blade in a heavy-duty gas turbine under different blowing ratios and mainstream turbulence conditions. Results show that under certain conditions, with the rise of hole spacing, the cooling air coverage reduces and the cooling efficiency lowers. The cooling effectiveness of the trailing edge is obviously higher than that of the leading edge due to the superposition effect from the leading edge. Under same hole spacing, the comprehensive cooling effectiveness of the moving blade increases with the rise of blowing ratio. When other conditions are fixed, in case of M=1.4, the greater the mainstream turbulence is, the lower the film cooling efficiency will be, however, the influence is relatively small.
  • Application of Acoustic Signals in Analysis of Lean Premixed Prevaporized Oscillation Combustion
    ZHANG Zilai, DU Shiqiang, GE Bing, SUN Peifeng, ZANG Shusheng
    2018, 38(2): 114-119.
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    To perform a feasibility study on application of acoustic signals in analysis of thermo-acoustic oscillation in a lean premixed prevaporized (LPP) combustor, an experimental LPP system was established, so as to carry out comparative tests for the thermo-acoustic parameters, and to conduct a modal analysis of the combustor. Results show that in the vicinity of basic frequency, a mutual coupling effect exists in the sound field of the combustion chamber and premixed chamber. At same inlet air velocities, the basic frequency of combustion chamber is proportional to the change of fuel flow rate, i.e. if the fuel flow rate keeps unchanged, the oscillation frequency of combustion chamber would remain the same. In transition conditions, the acoustic signal can reflect the variation states in the combustion chamber during ignition, stable to oscillation combustion, oscillation to stable combustion and flameout period. The main frequency of sound signals measured in the experiment is of the two order axial oscillation mode.
  • Real-time Online Diagnosis of Vibration Faults in Rotary Machineries
    FAN Jiaqing, XIAO Bole, GAO Sheng, ZHANG Qiang
    2018, 38(2): 120-126.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    To realize real-time online diagnosis of vibration faults in rotary machineries, some vibration signals were collected during operation of a unit, so as to calculate their characteristic values, determine the distribution of sensitivity levels, find the relationship between characteristic values and fault causes, set up database of characteristic values, and to verify the fault diagnosis model in a test rig. Results show that the model can achieve online analysis and diagnosis of vibration faults, which may serve as a reference for real-time local monitoring and intelligent remote diagnosis of vibration faults in rotary machineries, such as fans and water pumps, etc.
  • Effects of Laser Wavelength on Measurement of Trace Elements in Gas Using LIBS
    WANG Zhenzhen, ZHANG Zhenzhen, YAN Junjie, LIU Jiping, CHONG Daotong
    2018, 38(2): 127-131.
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    Laser-induced breakdown spectroscopy (LIBS) was used to measure the trace elements in gas, which has great potential in on-line measurement of trace elements. By setting up a LIBS exprimental system and taking the trace elements mercury and iodine as the objects of study, the trace elements in gas were measured and analyzed using LIBS under low-pressure and different laser wavelength conditions. Results show that the detection capability of LIBS can be significantly improved by lowering the pressure; at different pressures, the detection capability with laser of wavelength 532 nm for trace elements in gas is stronger than that with laser of wavelength 1 064 nm.
  • Experimental Study and Precision Comparison of Different Drift Loss Measurement Methods for Evaporative Cooling Equipment
    ZHANG Lixin, ZHUO Jing, GAO Ming, HE Rentu, SHEN Yan
    2018, 38(2): 132-137.
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    The circumferential unevenness at air outlet of evaporative cooling equipment was studied with an efficient water collection trough. To overcome the deficiency of single-layer filter paper method, a three-layer fan-shaped filter paper method was proposed, and subsequently experimental tests were conducted respectively by the method of efficient water collection trough, single-layer filter paper and three-layer fan-shaped filter paper, following which, their measurement precisions were compared. Results show that the precision of drifting measurement can be improved by adding circumferential testing points, or even by continuous rotation along the fan centerline. Three-layer fan-shaped filer paper helps to reduce the absorption weight and secondary drift loss. The drift loss mainly concentrates in the direction along the outlet radius from 0.71R to 0.75R.
  • Experimental Study on Heat-transfer Characteristics of Supercritical CO2 Fluid in Nickel-based Alloy Tubes at 700℃
    GE Xueli, ZHANG Zhongxiao, SHANG Xianyao, DONG Jiancong, FAN Haojie
    2018, 38(2): 138-144.
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    Convective heat-transfer characteristics of supercritical CO2 fluid in horizontal nickel-based alloy tubes of sizes d=15 mm and 10 mm were respectively studied in a test rig, while the effects of following factors on the convective heat-transfer coefficient were analyzed at wall temperature of 700℃, such as the medium pressure, medium temperature and mass flux, etc. Results show that the increase of medium pressure and mass flow rate can significantly improve the heat-transfer coefficient; when the pressure gets up to 8 MPa, the heat-transfer coefficient of tube 617 and tube 321 can reach 174.2 W/(m2·K) and 166.6 W/(m2·K), respectively. By comparing the expermental data and calculated results, it has been found that the caculation results of classical correlations are obviously deviated from experimental data, but the newly fitted correlation is relatively accurate, with a calculation error less than 12%.
  • Study on Fluidization Characteristics and Hysteresis Phenomena of Nanoparticles
    WANG Yuanbao, LIU Daoyin, WANG Zheng, CHEN Xiaoping
    2018, 38(2): 145-150.
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    To study the fluidization characteristics and hysteresis phenomena of nanoparticles, the fluidization behavior of following nanoparticles was investigated experimentally, such as the SiO2, Al2O3 and TiO2 nanoparticles, so as to find the difference of fluidization state and bed pressure drop of nanoparticles in the forward and reverse flow. Results show that under stable fluidization conditions, above three particles are different in bed pressure drop and fluidization state; SiO2 fluidization exhibits in the agglomerate particulate form, while Al2O3 and TiO2 fluidization are of the agglomerate bubbling type. For above three nanoparticles, there is a significant hysteresis in forward fluidization compared with the reverse fluidization. In the process of forward fluidization, the bed pressure drop and the expansion height fluctuate greatly, which are relatively stable in the reverse flow. By means of the design of "forward-backward-forward" fluidization experiments, it has been found that there is no hysteresis in the secondary forward flow of nanoparticles compared with the reverse fluidization, indicating that the hysteresis phenomena are mainly caused by the structure and cohesion of nanoparticles in the initial bed.
  • Design of a Supersonic Rotor Blade Working with Organic Fluids
    DAI Yongsheng, WANG Hongguang, HAN Tieying
    2018, 38(2): 151-155.
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    Based on the design theory for two-dimensional rotor blade with ideal gas, a real gas model was established for the design of supersonic rotor blade working with organic fluids. By using C++ to write the design program for rotor blade working with fluid R134a, under given conditions such as Mach number of import and export, the blade wall coordinates were obtained by calculation, and subsequently, a comparison was made for the blade profile respectively designed by ideal gas model and real gas model. Results show that when the operation point is close to the saturation line of R134a, the dense gas effect becomes strong, resulting in obvious difference in the design of rotor blades by above two models, whereas, when the operation point is far away from the saturation line, the dense gas effect becomes weak, resulting in little difference in the design. Numerical simulation results indicate that the real gas model is reasonable and feasible.
  • Calculation and Analysis on Oxidation Rates of Ferritic-Martensitic Steels in Supercritical Water
    SUN Li, YAN Weiping
    2018, 38(2): 156-162.
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    Based on an available space model of duplex oxide scale, the oxidation rates of two ferritic-martensitic steels were predicted in the environment of supercritical water at 400℃, 500℃ and 600℃, while the diffusion coefficients of iron in magnetite and Fe-Cr spinel were extrapolated at relatively low temperatures. Results show that the oxygen partial pressure at the magnetite/supercritical water interface meets the requirement of reaction equilibrium on equivalent oxygen partial pressure. The oxidation simulation results of NF616 steel at 500℃ and 600℃ and of HCM12A steel at 600℃ are found to be close to the experimental data, indicating that the consumption is basically effective. The relative error of HCM12A steel at both 400℃ and 500℃ between oxidation simulation and actual measurements is 40%, and its oxidation rate is less than that of EPRI by 1-2 orders of magnitude.
  • Experimental and Theoretical Study on the Shape of Long Bubbles in Horizontal and Near Horizontal Two-phase Slug Flows
    WU Zhicheng, XIONG Zhenqin, GU Hanyang
    2018, 38(2): 163-168.
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    The shape of long bubbles in horizontal and near horizontal two-phase slug flows was experimentally and theoretically studied, during which, the long bubbles were acquired by injecting isolated bubbles into the pipe of two different inner diameters, and their shape parameters were measured using parallel wire probes. Subsequently, a one-dimensional model was established to predict the shape of long bubbles, and the prediction results were compared with actual measurements. Results show that the shape of long bubbles depends on the liquid velocity, bubble length and the tube inclination. The prediction results obtained with the theoretical model agree well with actual measurements.