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Flow Analysis in Positive Displacement Micro-Hydro Turbine and Development of Low Pulsation Turbine
Kurokawa, Junichi,Matsui, Jun,Choi, Young-Do Korean Society for Fluid machinery 2008 International journal of fluid machinery and syste Vol.1 No.1
In order to extract micro hydropower in the very low specific speed range, a Positive Displacement Turbine (PDT) was proposed and steady performance was determined experimentally. However, the suppression of large pressure pulsation is inevitable for practical application of PDT. The objective of the present study is to reveal the mechanism and the characteristics of pressure pulsation in PDT by use of CFD and to suppress the pressure pulsation. Unsteady CFD analysis has revealed that large pressure pulsation is caused by large variation of rotational speed of the following rotor, while the driving rotor, which is output rotor, keeps constant speed. Here is newly proposed a 4-lobe helical type rotor which can reduce the pressure pulsation drastically and the performance prediction of new PDT is determined.
J-Groove Technique for Suppressing Various Anomalous Flow Phenomena in Turbomachines
Kurokawa, Junichi Korean Society for Fluid machinery 2011 International journal of fluid machinery and syste Vol.4 No.1
In operating a turbomachine at off-design conditions various instabilities caused by anomalous flow phenomena occur and sometimes lead to the damage of a turbomachine. In order to avoid these phenomena various devices characteristic to each phenomenon have been developed, however they make turbomachines large-sized and cause efficiency drop. The present author has developed a very simple and innovative device, termed "J-groove," of suppressing various anomalous flow phenomena commonly by controlling the angular momentum of the main flow. It has been revealed that J-groove makes an operation of a turbomachine stable in all flow range, causes little efficiency drop, and can be easily applied to an existing machine. Here is reviewed totally the results of suppressing various anomalous flow phenomena in turbomachines.
쿠로카와준이치(Junichi Kurokawa),최영도(Young-Do Choi) 한국유체기계학회 2005 유체기계 연구개발 발표회 논문집 Vol.- No.-
Cavitation is the most serious problem caused in developing high-speed turbopump, and use of an inducer is often made to avoid cavitation in main impeller. Thus, the inducer always operates under the worst condition of cavitation. If it could be possible to control and suppress cavitation in the inducer by some new device, it would also be possible to suppress cavitation occurring in all types of pumps. The purpose of our present study is to develop a new effective method of controlling and suppressing cavitation in an inducer using shallow grooves, named as "J-Groove". J-Groove is installed on the casing wall near the blade tip to use the pressure difference between high pressure region and low pressure region in the axial direction at the inlet of the inducer. The results show that proper combination of backward-swept inducer with J-Groove improves suction performance of turbopump remarkably in the range of partial flow rate as well as designed flow rate. The rotating backflow cavitation occurring in the range of low flow rate and the cavitation surge occurring in the vicinity of the best efficiency point can be almost fully suppressed by installing J-Groove.
부로카와준이치(Junichi Kurokawa),최영도(Young-Do Choi),자오린후(Linhu Zhao) 한국유체기계학회 2005 유체기계 연구개발 발표회 논문집 Vol.- No.-
Recently, micro hydropower attracts attention because of its clean, renewable and abundant energy resources to develop. However, suitable turbine type is not normalized yet in the range of micro hydropower and it is necessary to study for the effective turbine type. Moreover, relatively high manufacturing cost by the complex structure of the turbine is the highest barrier for developing the micro hydropower turbine. Therefore, a cross-flow turbine is proposed for micro-hydropower in this study because of its simple structure and high possibility of applying to low head. The purpose of this study is to further simplify the turbine structure and improve the performance, A guide vane is removed and the runner chamber is made compact using a new air supply method. The results show that the efficiency of the turbine is improved in a wide operating range and the size of the turbine is remarkably reduced.
극저비속도영역에서 원심펌프의 불안정성능 개선에 관한 연구
최영도(Young-Do Choi),쿠로카와준이치(Junichi Kurokawa),김유택(You-Taek Kim),이영호(Young-Ho Lee) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-
The ratio of disk friction loss in a centrifugal pump is very large for the total pump oss in the range of very low specific speed. Therefore, impeller radius should be shortened to increase the pump efficiency because the disk friction loss is proportional to the fifth power of impeller radius. In order to compensate the decreased head by the shortened impeller radius, vane angle at impeller outlet should be increased. However, as the vane angle at impeller outlet becomes larger, performance instability occurs at low flow rate regions. In this study, J-Groove is adopted to suppress the performance instability and detailed examination is performed for the influence of the J-Groove on the pump performance. The results show that J-Groove gives good effect on the suppression of performance instability. Moreover, as J-Groove increases pump head considerably, the pump size can be smaller.
최영도,쿠로카와준이치,Choi Young-Do,Kurokawa Junichi 한국유체기계학회 2006 한국유체기계학회 논문집 Vol.9 No.3
There are high expectations of improving the performance of a centrifugal pump in the range of very low specific speed which has been developed recently for the use instead of a conventional positive displacement pump. However, even though elaborated studies has been done for the pump intensively, the pump performance has not increased so much. Also, it is difficult to find detailed information from published literatures for suction performance of the very low specific speed centrifugal pump. Therefore, this study is aimed to improve the pump performance more and to make clear suction performance of the very low specific speed centrifugal pump. Recircular flow stopper is installed on the pump casing wall at the region of impeller outlet to improve the pump performance and J-Groove is also installed at the inlet of the pump casing for the purpose of suppressing occurrence of cavitation as well as improving pump performance. The result suggests that the simultaneous improvement of pump performance and suction performance of the very low specific speed centrifugal pump is possible by adopting optimum configuration of the recirculation flow stopper and J-Groove.
최영도(Young-Do Choi),쿠로카와준이치(Junichi Kurokawa),이영호(Young-Ho Lee) 한국유체기계학회 2007 유체기계 연구개발 발표회 논문집 Vol.- No.-
The purpose of present study is not only to develop a simple method to improve pump performance but also to suppress the occurrence of cavitation in the centrifugal pump by use of J-Groove. Semi-closed impeller is a newly developed centrifugal impeller in which inlet shape of the front shroud is modified. J-Groove is a shallow groove installed on the casing wall in the meridional direction. The results show that the application of the new type impeller of semi-closed impeller with J-Groove to a centrifugal pump has proved its effectiveness as a useful countermeasure of the unstable pump performance and cavitation. The combination of semi -closed impeller and J-Groove can be applied successfully and improves both the pump performance and suction performance.
윤재홍,이영생,흑주일재,구야순일,고교영명 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.4
MoSi₂ is a very promising high temperature structure material for its excellent oxidation resistance and mechanical properties at high temperatures with relatively low weight. For the extensive use of MoSi₂, however, problems such as pesting, disintegration of MoSi₂ during oxidation, should be taken care of. The initial step of posting in MoSi₂ is reported to occur by a simultaneous oxidation of Mo and Si, with some variation on the oxidation temperature. To investigate the posting in MoSi₂, this study focused on the simultaneous oxidation temperature of Mo and Si and the nucleation and growth of oxides formed at 593∼793 K. In this study, MoSi₂ was produced by spark plasma sintering(SPS) and then oxidized at 593∼1093K. The simultaneous oxidation of Mo and Si took place below 893 K while selective oxidation of Si occurred above 993 K. The weight gain of MoSi₂ was the highest at about 693 K. SEM analyses of the specimens oxidated at 693 K showed a lot of MoO₃, most of which were believed to be preicipitated at or around defects in matrix including SiO₂ particles.