• International Journal of Fluid Machinery and Systems
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• 제3권4호
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• pp.352-359
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• 2010

In recent years, the market has shown increasing interest in pump-turbines. The prompt availability of pumped storage plants and the benefits to the power system achieved by peak lopping, providing reserve capacity, and rapid response in frequency control are providing a growing advantage. In this context, there is a need to develop pumpturbines that can reliably withstand dynamic operation modes, fast changes of discharge rate by adjusting the variable diffuser vanes, as well as fast changes from pumping to turbine operation. In the first part of the present study, various flow patterns linked to operation of a pump-turbine system are discussed. In this context, pump and turbine modes are presented separately and different load cases are shown in each operating mode. In order to create modern, competitive pump-turbine designs, this study further explains what design challenges should be considered in defining the geometry of a pump-turbine impeller. The second part of the paper describes an innovative, staggered approach to impeller development, applied to a low head pump-turbine project. The first level of the process consists of optimization strategies based on evolutionary algorithms together with 3D in-viscid flow analysis. In the next stage, the hydraulic behavior of both pump mode and turbine mode is evaluated by solving the full 3D Navier-Stokes equations in combination with a robust turbulence model. Finally, the progress in hydraulic design is demonstrated by model test results that show a significant improvement in hydraulic performance compared to an existing reference design.

• International Journal of Fluid Machinery and Systems
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• 제4권3호
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• pp.334-340
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• 2011

Turbo-pumps have weak points, such as the pumping operation is unstable on the positive slope of the head curve and/or the cavitation occurs at the low suction head. To improve simultaneously both weak points, the first author invented the unique pumping unit composed of the tandem impellers and the peculiar motor with the double rotational armatures. The front and the rear impellers are driven by the inner and the outer armatures of the motor, respectively. Both impeller speeds are automatically and smartly adjusted in response to the pumping discharge, while the rotational torques between both impellers/armatures are counter-balanced. Such speeds contribute to suppress successfully not only the unstable operation at the low discharge but also the cavitation at the high discharge, as verified with the axial flow type pumping unit in the previous paper. Continuously, this paper investigates experimentally the effects of the tandem impeller profiles on the pump performances and the rotational speeds against the discharge, using the impellers whose loads are low and/or high at the normal discharge. The worthy remarks are that (a) the unstable operation is suppressed as expected and the shut off power is scarcely large in the smart control, (b) the blade profile contributes to determine the discharge giving the maximum/minimum rotational speed where the reverse flow may incipiently appears at the front impeller inlet, (c) the tandem impeller profiles scarcely affect the rotational speeds, while the loads of the front and the rear impellers are same, but (d) the impeller with the low load must run faster and the impeller with the high load must run slower at the same discharge to take the same rotational torque, and (e) the reverse flow at the inlet and the swirling velocity component at the outlet of the front impeller with the high load require making the rotational speed of the rear impeller with low load fairly faster at the lower discharge.

• International Journal of Fluid Machinery and Systems
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• 제4권2호
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• pp.217-222
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• 2011

The rotordynamic fluid forces acting on a closed type impeller in whirling motion were measured and the influence of the clearance geometry on the stability of the impeller was examined. At small positive whirling speed, the rotordynamic forces acted as destabilizing forces for all casings. A small clearance between the shroud of the impeller and the casing caused large fluid force, but did not change the destabilizing region. Radial grooves in the clearance were effective for reducing the fluid forces and destabilizing region due to the reduction of the circumferential velocity without the deterioration of the pump performance. A rotating phenomenon like a rotating stall of the impeller occurred at low flow rate and the resonance between it and the whirling motion led to a sudden increase in force at the whirling speed ratio of 0.7.

• 동력기계공학회지
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• 제3권2호
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• pp.13-19
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• 1999

The purpose of the present experimental study is to apply multi-point simultaneous measurement by PIV(Particle Image Velocimetry) to high-speed flow region within a domestic boiler circulation pump. Two different kinds of flow rate($27{\ell}/min,\;19{\ell}/min$)are selected as experimental condition. A volute casing and Impeller made of transparent Polycarbonate were made for the easy access of the illumination laser via fiber optical line and cylinder lens assembly to the measuring region. A CCD camera is syncronized with AOM to acquire clear original particle images. Optimized cross correlation identification to obtain velocity vectors is implemented by direct calculation of correlation coefficients. The instantaneous and time-mean velocity distribution, velocity profile and kinetic energy are represented quantitatively at the full-scale region for the deeper understanding of the unsteady flow characteristics in a commercial circulation pump.

• International Journal of Fluid Machinery and Systems
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• 제7권3호
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• pp.94-100
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• 2014

In double-suction centrifugal pumps, it was found that cavitation instabilities occur with vibration and a periodic chugging noise. The present study attempts to identify cavitation instabilities in the double-suction centrifugal pump by the experiment and Computational Fluid Dynamics (CFD). Cavitation instabilities in the tested pump were classified into three types of instabilities. The first one, in a range of cavitation number higher than breakdown cavitation number, is cavitation surge with a violent pressure oscillation. The second one, in a range of cavitation number higher than the cavitation number of cavitation surge, is considered to be rotating cavitation and causes the pressure oscillation due to the interaction of rotating cavitation with the impeller. Last one, in a range of cavitation number higher than the cavitation number of rotating cavitation, is considered to be a surge type instability.

• International Journal of Fluid Machinery and Systems
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• 제9권2호
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• pp.107-118
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• 2016

This paper focuses on the single stage and multistage performance characteristics of centrifugal mixed flow submersible borewell pump. This study reveals that the performance of single stage pump is higher than that of multistage pumps. The head, input power and efficiency of single stage pump are higher than the per stage head, per stage input power and efficiency of multistage pumps. This study is divided into three parts. In the first part, five prototype pumps were made in single stage and multistage construction and the performance tests were conducted. In the second part, numerical validation has been done for different turbulence models and grid sizes. k-Omega SST model has been selected for the performance simulation and was validated with the performance of the test pump with static pressure tappings. In the third part, single and three stage pump performance were simulated numerically and compared with experimental results. The detailed analysis of pressure and velocity distributions reveals the difference in performance of single and three stage pump, due to non-uniform flow and difference in averaged flow velocities at the subsequent impeller inlets except the 1st stage impeller inlet.

• International Journal of Fluid Machinery and Systems
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• 제2권3호
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• pp.189-196
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• 2009

The effect of inlet and outlet blade angles on a micro regenerative pump head was examined in experiments. The pump head was little increased by changing the blade angles compared with the original pump with the inlet and outlet blade angles of 0 degree. The effect of the axial clearance between the impeller and the casing on the pump head was also examined. The head was increased largely by decreasing the axial clearance. The computation of the internal flow was performed to clarify the cause of the increase of the pump head due to the decrease of the clearance. The local flow rate in the casing decreased as the leakage flow rate through the axial clearance decreased due to the decrease of the clearance. It was found that the larger head in the smaller clearance was just caused by the smaller local flow rate in the casing. In the case of the smaller clearance, the smaller local flow rate caused the smaller circumferential velocity near the front and rear sides of the impeller. This caused the increase of the angular momentum in the casing and the head.

• 한국초전도ㆍ저온공학회논문지
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• 제20권3호
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• pp.28-33
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• 2018

With the continuous performance improvement and commercialization of HTS wires, there have been many efforts to commercialize HTS power cables recently. Unlike conventional power cables, a cryogenic cooling system is required for a HTS power cable and a cryogenic pump is one of the essential components to circulate subcooled liquid nitrogen and cool the HTS power cable. Especially, the development of a reliable and high-efficiency cryogenic pump is an important issue for the commercialization of HTS power cables of several kilometers or more. In this study, we designed and fabricated a cryogenic pump for subcooled liquid nitrogen with a mass flow rate of 1.2 kg/s, a differential pressure of 5 bar, and evaluated the hydraulic performance of the pump. Impeller design was conducted to meet the target design performance with 1 D analysis model and CFD analysis. The pump performance parameters such as pressure heads, mass flow rates, and efficiencies in accordance with rotating speeds were assessed using a laboratory's performance evaluation system.

• Journal of Advanced Marine Engineering and Technology
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• 제39권3호
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• pp.248-254
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• 2015

국내에는 아직 침수선박 구조용 대용량 배수펌프에 대한 기술개발 사례가 없는 상황이다. 현재 침수선박 구조를 위해 농업용 배수펌프가 사용되고 있으나 실효성이 현저히 떨어지며, 낮은 배수량, 이물질 걸림 현상, 겨울철 운전 오작동 등의 문제점이 있다. 따라서 본 논문에서는 해양에서 신속한 침수선박의 구조를 위해 현재 장비가 가지는 문제점을 개선하여 분당 20 톤의 배수량을 가지는 대용량 배수펌프 시스템을 개발하고자 한다. 대용량 배수펌프 시스템은 펌프 배출구를 통해 배출되는 흡입양정 8 m에서 분당 20 톤의 해수를 배출하는 것을 목표로 배수펌프 시스템 설계 및 개발을 수행하였다. 펌프종류는 조선해양 분야에서 액체를 이송하는데 가장 많이 사용되는 원심펌프를 채택하였으며, 요구 시방을 기초로 펌프를 설계하였다. 임펠러 블레이드는 요구 시방과 Stepanoff 설계 상수를 이용하여 임펠러 제원과 블레이드 입출구각을 도출하였고, 설계된 임펠러와 하우징 형상에서 목표 유량 만족 여부를 확인하기 위해 유동해석을 수행하여, 임펠러 회전수에 따른 유량을 검토하였다. 또한 실제 운전 중에 발생할 수 있는 제품에 대한 구조적인 취약성을 판단하기 위해 임펠러 구조해석을 수행하여 안전성을 검토하여, 침수선박 구조를 위한 배수펌프 시스템 개발을 완료하였다.

• 항공우주기술
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• 제6권2호
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• pp.205-210
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• 2007

75톤급 액체 로켓 엔진용 터보펌프의 산화제펌프에 대한 로터다이나믹 설계를 수행하였다. 인듀서와 임펠러 및 베어링의 축배치는 항우연에서 개발 중인 유사한 구조를 가지는 터보펌프를 근간으로 하였고, 75톤급 산화제펌프 수력 설계에 맞추어 인류서, 임펠러의 축길이가 반영되었다. 후방 베어링으로부터 임펠러까지의 거리를 베어링 하중 설계에 대한 설계 변수로 고려하였고, 전방 베어링과 후방 베어링의 강성을 변화시키면서 회전 속도에 따른 비동기 고유진동수 해석을 수행하여 산화제 펌프의 임계속도를 고찰하였다. 베어링에 적절한 하중이 부과된다면 산화제 펌프의 임계속도는 기준속도 11,000 rpm과 비교하여 충분히 높기에, sub-critical 로터로서 기준속도 이내에서 안정적인 터보펌프의 운용이 가능하리라 판단된다.