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Three-dimensional unsteady cavitating flows around an axisymmetric body with a blunt headform
Changli Hu,Guoyu Wang,Guanghao Chen,Biao Huang 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.3
We investigated the three-dimensional characteristics in the unsteady cavitating flow over an axisymmetric body with a blunt headform. A high-speed video camera was used to visualize the cavitating flow structures. A modified PANS (Partially-averaged Navier-Stokes) turbulence model coupled with Kubota cavitation model was used to simulate the time-evolution process of the unsteady cavitatingflows. The finite-time Lyapunov exponent (FTLE) and Lagrangian coherent structures (LCS) methods are applied to investigate thethree-dimensional flow patterns. The results show that the numerical method is capable of simulating the unsteady cavitating flow forcapturing the attached cavity with maximum-length, the cavity break-off and U-type shedding, in accordance with the qualitative featuresobserved in the experiment. Three-dimensional characteristics are extremely impressive in the unsteady cavitating flows. The re-entrantflows originate from different circumferential positions at the closure region of the attached cavity, and move upstream at differentspeeds. Moreover, substantial circumferential motions in the unsteady cavitating flow are found based on Lagrangian trajectories, and itis reasonably deduced that the U-type shedding cavity is primarily induced by the effect of re-entrant flow motions consisting of movingupstream and circumferential flows as well.
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Changli Hu,Guoyu Wang,Xuede Wang,Biao Huang 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.7
Experiments have been performed to study the inception cavitation phenomena in the separated flows adjacent to two axisymmetric bodies whose forebodies are blunt and conical respectively. A high-speed video camera was used to visualize the dynamic process of incipient cavitation, and the PIV (Particle imaging velocimetry) technology was applied to measure the velocity field, the vorticity and turbulence fluctuations under non-cavitation and inception cavitation conditions. Observations suggest that incipient cavities around the two axisymmetric bodies have the similar onset appearance but different development patterns and cycles with different inception cavitation index. Also, it is found that incipient cavities are always located within the separated vortex upstream the reattachment point during the whole dynamic process, and the scale of separation vortex greatly influences the positions where incipient cavities generate and collapse. Measures of the turbulence fields show that the distribution of vorticity can be changed by unsteady incipient cavities, and inception cavitation causes slight uniformity of velocity in shear layer and conspicuous increase of turbulent fluctuations. Compared to that of the conical headform, inception cavitation around the blunt headform presents more vortical traits and turbulence fluctuations.
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Changli Hu,Xuede Wang,Guoyu Wang,Youquan Cao 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.1
The objective of this paper is to investigate the cavity shedding dynamics in unsteady cavitating flows around an axisymmetric body with a blunt headform. A high-speed video camera is used to record the cavity evolution process. The numerical simulations are performed based on the homogenous method coupled with a modified PANS (Partially-averaged Navier-Stokes) turbulence model and Zwart cavitation model. The results show that the predicted time-evolution process of cavity agree fairly well with the corresponding experimental data for two different cavitation numbers ( s = 0.7 and s = 0.6 ). Compared to that of s = 0.6 , the cavity shedding behavior of s = 0.7 presents more fluctuations and instabilities. To elucidate the different shedding structures, the Lagrangian coherent structures (LCS) and particle trajectory methods are also utilized here. It is found that the particle tracers respectively demonstrate the cavity shedding behaviors of conjunction at s = 0.6 and rolling up at s = 0.7 . Moreover, the LCS distributions vary with the timeevolution of vortex structures. The particle trajectories can illustrate the upstream and downstream vortex structures connect together at s = 0.6 but separate at s = 0.7 , which highly consistent with the cavity shedding behaviors.
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Construction of Ecological English Class in University of Physical Education
( Changli Li ) 한국체육학회 2015 국제스포츠과학 학술대회 Vol.2015 No.1
Purpose: Based on ecological perspectives, the paper makes a combined study of education of college students in physical university of sports and English teaching in this kind of universities. Taking the unsatisfactory ecology awareness in sports events and sports objects, a new kind of ecological English class should be constructed immediately in order to promote the humanities and ecological awareness in college students majoring in sports. On the one hand, English teaching and learning efficiency can be improved, and on the other hand, this new kind of class will contribute to ecologilization of sports and its sustainable development. Method: Firstly, through literature retrieval, research and related reference books about education ecology, system ecology, and sports ecology should be gathered to get a full understanding of theory frontier. Secondly, questionnaires are conducted to gathered information about demands of students, rate of satisfaction about English class, influence of English class upon the overall quality of college students, their understanding of ecology, trying to establish close relationship between English teaching and sports` sustainable development. Thirdly, through interview with experts and scholars in the fields of both English teaching and sports education, this study tries to get their understanding of education ecology, sports ecology and English teaching, analyzing the possibility to improve sustainable development of sports through construction of ecological English class. Result: Firstly, sports plays an increasingly important role in strengthening physical health and deepening friendship and understanding among human beings, and sports, in return, will further promote development of economy and cultural prosperity. College students majoring in sports get more access to international sports events, thus they are fully aware of the importance of English and have great demand of learning English. Secondly, As most of the time and energy has been spent on exercising, students majoring sports have little time to improve their English; consequently, their actual use and performance of English is not satisfactory, and this will further decrease their confidence. Besides, traditional English class is difficult to arouse their interest in English learning and therefore hard to make them get involved in English learning. Thirdly, Students in sports colleges are the main body in sports events, coaches and teachers; however, their understanding of ecology is confined in external environmental ecology, most of them fail to understand social ecology and psychological ecology, and fail to catch the relationship between ecology and sustainable development of sports as well as themselves. Conclusion: Firstly, organic ecology theory believes that any system must be open so that information exchange with external energy can be obtained, then survival and development becomes possible. College English class have to break the limit of space and time, students have to learn in an open ecosystem, and the class should extend to the whole society; in this way, the correlation between in-class learning and after-class application, and in-class teaching and interaction with outside society is closely related. Secondly, ecological college English classroom is based on harmonious and relaxed atmosphere, and teachers strive to create a multi-dimensional interaction between the teacher and individual student, between different groups through both cooperation and competition. Just like in a sports contest, all students are equipped with a strong sense of belonging and confidence to achieve a collective purpose. Ecological college English classroom has a good nourishing function, aiming at a healthy and sustainable growth of all ecology subjects in an equal, collaborative, and open atmosphere. Thirdly, ecological development emphasizes that development is a gradual and orderly system development. The purpose of the college English classroom should play a function in social service. Therefore, effective teaching strategies should be adopted to ensure a gradual and orderly development of students` language capacity, and increase their knowledge realm. Under the guidance of ecological perspective, college English, as a branch of humanities, has to cultivate students` humanities and their ecological ideas. This responsibility should never be neglected and abandoned. Through team work and multimedia display, taken sports ecology and sports ethics as teaching content, English class as a bridge strengthens students` ecology awareness and eventually promote sustainable development of sports and the whole of society.
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POWER GTO WITH COMPENSATED RING ANODE-SHORT
Zhang Changli,Chen Zhiming,S.C.Kim,W.G.Min,J.M.Park,N.K.Kim,E.D.Kim 전력전자학회 1998 ICPE(ISPE)논문집 Vol.- No.-
This paper gives the novel design of compensated ring anode-short for power GTO thyristor. By means of this design the power GTO of Φ63.5mm 2500A/4500V reaches more uniform turn-off compared with conventional ring shorts GTO, resulting in higher turn-off ability and low tail current/tail time.<br/>
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High Power Gto Thyristors with the New Anode-Shorts Structure
Zhang Changli,Wu Jijun,Chen Zhiming 전력전자학회 1995 ICPE(ISPE)논문집 Vol.1995 No.10
An 1000-A 3000-V gate turn-off thyristor( GTO) with the ringed anode-shorts has been developed. To achieve the low on- state voltage and switching loss, the optimum device design and processing technologies are presented here. It is also confirmed that the device with ringed anode- shorts has a faster decay rates which have strongly effects on the switching loss. As a result, the improved device design gives more reliability than that of symmetrical GTO during the turn-off period.
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SOFT RECOVERY CHARACTERISTICS OF POWER DIODE BY PROTON IRRADIATION
Zhang Changli,Chen Zhiming,J.M.Park,W.G.Min,S.C.Kim,N.K.Kim,E.D.Kim 전력전자학회 1998 ICPE(ISPE)논문집 Vol.- No.-
The soft reverse recovery characteristics of P-I-N power diodes by different lifetime killer were compared in this paper. It was concluded that the best local lifetime control at N" base was achieved through the optimization of penetrated depth into the wafer by 5 MeV proton irradiation, resulting in significant soft recovery performance in our study. The results of 5~12 MeV electron irradiation and platinum diffusion were also discussed here.<br/>
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