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- 저자 : Jiaxing Ren (검색결과 2 건)
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The characteristics investigation under the unsteady cavitation condition in a centrifugal pump
Jiaxing Lu,Shouqi Yuan,Parameswaran Siva,Jian-Ping Yuan,Xudong Ren,Banglun Zhou 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.3
Numerical simulation and experimental method are combined to investigate the pump inlet and outlet pressure fluctuations, the vibration characteristics and the internal flow instabilities under the unsteady cavitation condition in a centrifugal pump. It is found that the unsteady cavitation starts to generate as the NPSHa is lower than 5.93 m. Apparent asymmetric and uneven cavity volume distribution on each blade and in the impeller can be observed as the NPSHa decreases from 4.39 m to 1.44 m, which includes the cavitation develops from cavitation surge, rotating cavitation to asymmetric cavitation. The flow vortexes in each blade channel are produced in the cavity trailing edges by the shedding and collapse of cavitation, which interfere with each other and aggravate the flow instabilities. The dominant frequencies of the pump inlet and outlet pressure fluctuations are the shaft frequency and blade passing frequency under the unsteady cavitation conditions, respectively. Broadband pulses are obtained from both the pump inlet and outlet pressure pulsations, which results from the random shedding and collapse of unsteady cavitation bubbles. Obvious corresponding relationship between the root mean squares of the vibration measured in different positions and the suction performance curve is found under both the non-cavitation and unsteady cavitation conditions.
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Xiaowei Wang,Jiaxing Ren,Xinyu Hu,Xingyu Gu,Ning Li 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.6
The compaction characteristics of porous asphalt (PA) mixtures are significantly different from those of traditional dense-graded asphalt mixtures. Compaction efforts are critical for PA mixtures to exhibit good performance in terms of strength, functionality, and durability. The objective of this study was to determine the optimum number of gyrations for typical PA mixtures compacted using a Superpave gyratory compactor. The compaction characteristics and the influence of seven gyration levels on the indicators of air voids (AV) content, Marshall Stability (MS), multi-directional permeability, stone-on-stone contact, and durability of PA mixture were investigated through laboratory experiments. A multi-directional permeameter was designed to evaluate the multi-directional permeability of PA mixtures, including vertical, horizontal, and combined horizontal-vertical permeability. The AV content, multi-directional permeability decreases with the increasing gyrations. Based on the requirements of each indicator, the minimum and maximum gyrations for each indicator were determined. Balancing the performance of strength, functionality, and durability, the optimum number of gyrations for the PA mixtures was determined to be between 45 and 75 gyrations, which allows for different gyrations depending on the application of the PA mixture. Finally, the requirements of MS, horizontal permeability, and combined horizontal-vertical permeability are recommended for improving the performance of PA mixture.
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