CFD ANALYSIS AND REDESIGN OF THE FRANCIS TURBINE WITH LARGE HEAD VARIATION

GUO PENGCHENG,LUO XINGQI,LIU SHENGZHU 한국수자원학회 2005 한국수자원학회 학술대회 Vol.2005 No.1

Influence of tip clearance on pressure fluctuations in an axial flow pump

Jianjun Feng,Xingqi Luo,Pengcheng Guo,Guangkuan Wu 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.4

Rotor-stator interaction in axial pumps can produce pressure fluctuations and further vibrations even damage to the pump system in some extreme case. In this paper, the influence of tip clearance on pressure fluctuations in an axial flow water pump has been investigated by numerical method. Three-dimensional unsteady flow in the axial flow water pump has been simulated with different tip clearances between the impeller blade tip and the casing wall. In addition to monitoring pressure fluctuations at some typical points, a new method based on pressure statistics was proposed to determine pressure fluctuations at all grid nodes inside the whole pump. The comparison shows that the existence of impeller tip clearance magnifies the pressure fluctuations in the impeller region, from the hub to shroud. However, the effect on pressure fluctuation in the diffuser region is not evident. Furthermore, the tip clearance vortex has also been examined under different tip clearances.

Torsional Vibration Analysis of Hydro-Generator Set Considered Electromagnetic and Hydraulic Vibration Resources Coupling

Zhiqiang Song,Yunhe Liu,Pengcheng Guo,Jianjun Feng 한국정밀공학회 2018 International Journal of Precision Engineering and Vol.19 No.7

The torsional vibration characteristics of the hydro-generator set considering the electromagnetic and hydraulic vibration resources coupling are studied. The moment of rotation consists of water flow driving and magnetic torques caused by the air gap magnetic field in the generator rotor in the case of ignoring the mechanical friction. A coupling torque vibration model of hydro-generator shaft system was established. The model considered the coupling action of hydraulic and electromagnetic excitations, as well as the elastic effect of rotor spiders. The influences of the rotor moment inertia, rotor stiffness, and mass of turbine water added into the torsional natural vibration of the unit shaft system were studied. The effect of hydraulic excitation frequency on torsional vibration response was also investigated. The frequency response curves of shaft torque, torsional vibration angle, and electromagnetic torque were presented. The electromagnetic and hydraulic coupling resonance was studied when hydraulic excitation frequency was equal to zero and first-order frequencies. The excitation electric current and internal active power angle on torsional vibration was further analyzed. This study provides an analysis model and method considering the coupling of electromagnetic and hydraulic vibration resources for design and stable operation of water turbine generator sets.

Numerical Investigation on a Twin-Screw Multiphase Pump Under low IGVF

Shuaihui Sun,Pengbo Wu,Pengcheng Guo,Guangzhi Yi,Ahmed Kovacevic 한국유체기계학회 2021 International journal of fluid machinery and syste Vol.14 No.4

A three-dimensional transient numerical model was developed to obtain the two-phase flow characteristics in a twin-screw multiphase pump based on dynamic mesh technology and the multiphase flow model. The pump performance under different inlet gas volume fractions (IGVF) was predicted by the numerical model and was tested. Then, the numerical model was validated after comparing the simulation and experimental results. After that, the flow field in the pump under 10% IGVF was analyzed. When the IGVF is 10%, the pressure increases step by step and is symmetrical from both ends to the middle of the screw rotors. The pressure distribution through a single working chamber is uniform. It falls rapidly at the inlet of the tooth tip gap and then drops linearly in the gap channel. At the outlet of the tip gap, the pressure temporarily falls due to the high-speed jet. The GVF distribution in the working chamber is uneven. The leakage flow is laminar in the tip gap, and the liquid concentrates on the top of the gap. When the last working chamber connects with the discharge chamber, the discharge jet flow causes the vortices in the discharge pipe. The gas gradually moves to the center of the vortices, forming four gas-phase aggregation regions. The velocity of the interlobe leakage is the largest. The maximum velocity appears at the second cross-section and reaches 35m/s. This research can be used to improve the performance of the twin-screw multiphase pump under two-phase working conditions.

Experimental Study of Seismic Damage with Park-Ang Model for Recycled Aggregate Concrete Columns

Yujiang Fan,Ziqiang Guo,Yachao Wang,Pengcheng Zhao,Binshan Yu 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.9

By means of the low cycle loading tests on six recycled aggregate concrete (RAC) columns with different proportions, in combination with the Park-Ang two-parameter damage model suitable for ordinary concrete columns and the damage degree Dc of actual structures, the calculated value of cyclic loading coefficient β of recycled aggregate concrete columns was determined. It would be achieved by analyzing the calculated β that the impact of the replacement ratio of recycled aggregate and the content of mixed fibers on β was significantly different. Considering the reinforcement ratio mentioned in paper. Matlab was further employed to fit multivariable linear equation regarding recycled aggregate replacement ratio, mixed fibers contents and reinforcement rate as the basis, so that the computation formula of the cyclic loading coefficient β suitable for recycled aggregate concrete columns was revealed.

Experimental study on fabrication of large-scale micro cylinders array by mask jet electrochemical deposition

Ting Huang,Zhongning Guo,Guiming Liang,Shunzhi Qiao,Pengcheng Cai,Zhixiang Zou 대한기계학회 2023 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.37 No.8

The mask jet electrochemical deposition was used to deposit the large-scale micro cylinders array in this study. The effect of the pulse peak current density, pulse frequency, pulse duty cycle, injection pressure and scanning speed on the deposition characteristics (i.e. deposition height, surface roughness and surface quality of micro cylinders) have been investigated. The experiment results showed that the mean height and the surface roughness of micro cylinders increased form the peak current density. Moreover, due to a high pulse frequency provided a shorter pulse on-time, and significantly facilitating the renewal of the ion concentration in the electroforming fluid. A higher pulse frequency and larger duty cycle provide a better deposition characteristic. The injection pressure was found to have a significant effect on the height, the surface roughness and surface appearance of micro cylinders. Furthermore, when using higher scanning speed, the crystalline particles of the cast layer decrease, significantly decreasing the surface roughness. Based on discussed, the pulse current density of 12 A/dm 2 , a pulse frequency of 3000 Hz, a pulse duty cycle of 30 %, a jet inlet pressure of 80 kPa, a scanning speed of 8 mm/s and a number of scans of 100 is optimal parameters. Finally, by using these parameters, a large-area micro cylindrical array structures with a height of 22.53±2.46 μm and diameter of 205±3.21 μm were successfully fabricated. It can be concluded that the mask jet electrochemical deposition is a simple method to realize the electrodeposition of large-area array structures.

Numerical Analysis of Two-Phase Flow in a Micro-Hydraulic Turbine

Tiejun Chen,Shuaihui Sun,Ye Pang,Pengcheng Guo 한국유체기계학회 2019 International journal of fluid machinery and syste Vol.12 No.4

In many industrial processes such as natural gas processing, seawater desalination et al, there is a large amount of liquid waste pressure energy, which can be converted into electric or mechanical energy by a micro-hydraulic turbine. But its efficiency and stability will deteriorate when the working fluid contains gas. Aiming at improving the hydraulic efficiency of the micro-turbine, the three-dimensional transient two-phase flow model which adopts the shear-stress-transport (SST) model as turbulence model and Eulerian-Eulerian model as two-phase flow model with the commercial code ANSYS-CFX was established and solved to study the two-phase flow characteristics of the micro-hydraulic turbine with fixed guide vane openings under different gas volume fraction (GVF). The numerical simulation results show that the power and efficiency of the turbine decrease by 24% and 21% respectively when the inlet GVF is 0.20. The area of low pressure in each impeller passage increases with the inlet GVF, and the pressure difference between the working and suction surface of the blade decreases. The GVF distribution in impeller passage is asymmetrical, which is caused by the gas-liquid separation in the volute. At the left lower part of impeller passage, the gas accumulates at the suction surface of the blades under the Coriolis force and its GVF reaches 90%. The asymmetrical GVF distribution will result in the asymmetrical pressure distribution in the impeller passage, which leads to the imbalance force on the blades. Moreover, the asymmetrical GVF distribution will reinforce the positive incidence at the lower part of impeller passage, and weaken it at the upper right impeller passage. The volute should be redesigned to ensure the uniform gas distribution at the inlet of each impeller passage.

Performance of Cone Meter for Measuring Cryogenic Fluid Considering Cavitation

Denghui He,Zhuang Chang,Bofeng Bai,Senlin Chen,Pengcheng Guo 한국유체기계학회 2019 International journal of fluid machinery and syste Vol.12 No.1

The performance of the cone meter when measuring the cryogenic fluid was investigated by numerical simulation. The results show that the discharge coefficient and pressure loss coefficient of the cone meter are almost constant when the Reynolds number in the “stable region”. The cryogenic fluids, especially the liquid hydrogen, have wider stable Reynolds number ranges than the water. There is little effect of cavitation on the discharge coefficient and pressure loss coefficient at the initial stage of cavitation. Thus the effect of slight cavitation on the measurement error of the flow rate is small, whose relative error is less than ±0.5% in present cases. This study opens a new avenue for measuring the flow rate of the cryogenic fluid.