• International Journal of Fluid Machinery and Systems
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• 제8권4호
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• pp.230-239
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• 2015

The swirling flow in the draft tube of a Francis turbine can cause the flow instability and the cavitation surge and has a larger influence on hydraulic power operating system. In this paper, the cavitating flow with swirling flow in the diffuser was studied by the draft tube component experiment, the model Francis turbine experiment and the numerical simulation. In the component experiment, several types of fluctuations were observed, including the cavitation surge and the vortex rope behaviour by the swirling flow. While the cavitation surge and the vortex rope behaviour were suppressed by the aeration into the diffuser, the loss coefficient in the diffuser increased by the aeration. In the model turbine test the aeration decreased the efficiency of the model turbine by several percent. In the numerical simulation, the cavitating flow was studied using Scale-Adaptive Simulation (SAS) with particular emphasis on understanding the unsteady characteristics of the vortex rope structure. The generation and evolution of the vortex rope structures have been investigated throughout the diffuser using the iso-surface of vapor volume fraction. The pressure fluctuation in the diffuser by numerical simulation confirmed the cavitation surge observed in the experiment. Finally, this pressure fluctuation of the cavitation surge was examined and interpreted by CFD.

• Journal of Advanced Marine Engineering and Technology
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• 제36권3호
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• pp.351-357
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• 2012

Small hydropower is a reliable energy technology to be considered for providing clean electricity generation. Producing electrical energy by small hydropower is the most efficient contribution to renewable energy. Cross-flow turbine is adopted primarily because of its simple structure and high possibility of applying to small hydropower. The purpose of this study is to investigate the effect of inlet nozzle shape on the performance and internal flow of a cross-flow turbine for small hydropower by CFD analysis. Moreover, the shape effect of draft tube has been investigated according to modified shapes of the length and the diffuse angle. The results show that relatively narrow and converging inlet nozzle shape gives better effect on the performance of the turbine.

• 한국농업기계학회:학술대회논문집
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• 한국농업기계학회 1993년도 Proceedings of International Conference for Agricultural Machinery and Process Engineering
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• pp.307-315
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• 1993

A direct draft measurement system was developed based on the swingle tree- the rear component of the single-animal harnessing (or yoking) system . The prototype was made from a tube, on which four strain gages were attached. The pull of the draft animal through the flexible pull chains or ropes causes the beam to bend, The bending strain is sensed by the strain gages and the bridge converts this to a voltage signal. Counterweights keep the tube correctly oriented if the angle of pull changes , while end bearing follow the variations in the angle of pull. Hence, the voltage output is proportional to the draft. the device has highly linear response, acceptable sensitivity negligible error and hysteresis. It is suitable for electronic data acquisition, non-intrusive , easy to attach and detach and is reasonably priced.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 1993년도 추계학술발표회 초록집
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• pp.42-45
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• 1993

내경 0.1 m 의 draft tube 를 갖는 직경 0.3 m, 높이 2.7 m 인 내부순환유동층 가스화반응기에서 호주산 준 역청탄을 공기와 수증기를 사용하여 가스화 하였다. draft tube에 공기를 주입하여 연소반응, annulus 구역에 수증기를 주입하여 가스화하여 연소반응에서 생성된 열을 annulus 에 공급하였다. 반응기온도와 석탄주입량에 따라 H$_2$, CO 및 발열량이 증가하였으나 공기의 유량증가에 따른 H$_2$, CO는 감소하고 $CO_2$ 는 증가하였으며 발열량은 감소하였다.

• 신재생에너지
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• 제16권2호
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• pp.35-46
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• 2020

Recently, turbines operating in hydro power plants are required to undergo renovation and modernization due to their age exceeding 30 years. In the process of renovation or modernization, a performance test of the scaled-down model is necessary to verify the performance of the real-size model. This model test method, with criteria that is similar to that of a real turbine, is the most economical and important method. Furthermore, the shapes of the runner and guide vane can be modified or replaced easily. However, during the process of modernization, the components with the spiral casing and draft tube are impossible to repair or replace because of the buried ground. Thus, in this study, numerical analysis is conducted to investigate the hydraulic performance based on the difference between the two-dimensional computer-aided design (CAD) shape and the real three-dimensional scan shape of the spiral casing and draft tube.

• Membrane and Water Treatment
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• 제2권2호
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• pp.105-119
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• 2011

This study presents the tests of an Immersed Membrane BioReactor (IMBR) equipped with a draft tube and focuses on the influence of hydrodynamic conditions on membrane fouling in a pilot-scale using a hollow fiber membrane module of ZW-10 under ambient conditions. In this system, the cross-flow velocities across the membrane surface were induced by a cylindrical draft-tube. The relationship between cross-flow velocity and aeration strength and the influence of the cross-flow on fouling rate (under various hydrodynamic conditions) were investigated using Multi-Dimension Scaling (MDS) analysis. MDS technique is especially suitable for samples with many variables and has relatively few observations, as the data about Membrane Bio-Reactor (MBR) often is. Observations and variables are analyzed simultaneously. According to the results, a specialized form of MDS, CoPlot enables presentation of the results in a two dimensional space and when plotting variables ratio (output/input) rather than original data the efficient units can be visualized clearly. The results indicate that: (i) aeration plays an important role in IMBR performance; (ii) implementing the MDS approach with reference to the variables ratio is consequently useful to characterize performance changes for data classification.

• 한국유체기계학회 논문집
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• 제18권1호
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• pp.11-19
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• 2015

Recently, the cross flow turbines attract more attention for their good performance over a large operating regime at off design point. This study employs a very low head cross flow turbine, which has open inlet duct and has barely been studied before, to investigate the performance of the cross flow turbine with air suction from the rear part of the runner. Unlike conventional cross flow turbines, a draft tube is attached to the outlet of runner to improve the turbine performance. Water level and pressure in the draft tube are monitored to investigate the influence of air suction. Torque at local blade passage of three parts of runner is examined in detail under the conditions of different air suction. Consequently, it is found that with proper air suction in the runner chamber, the water level in the draft tube gradually drops to Stage 2 of the runner and the efficiency of the turbine can be raised by 10%. Overall, the effect of air-layer on the performance of the turbine is considerable.

• 한국수자원학회논문집
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• 제38권5호
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• pp.365-377
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• 2005

본 연구는 수력발전시설에서 물고기의 생존과 상해를 유도하는 흐름현상을 파악하기 위한 진보된 수치해석기법의 개발을 다루고 있다. 원형 젤의 LES를 실시하여 난류젤의 전단지역에 물고기를 방류하는 실험의 결과를 수치적으로 해석하였다. 이 연구에서는 순간 LES 흐름장이 유속, 압력 그리고 와도의 강한 변동으로 특성지울 수 있으며, 이것이 물고기에게 시간평균 정상류보다 상당히 큰 추진력과 모멘트를 발휘함을 보여준다. 이 연구는 아울러 수력터빈 드래프트관에서의 부정류를 RANS/LES의 혼성모형 즉 DES를 이용하여 해석하였으며, 물고기가 드래프트관내에서 방향감각을 상실하거나 과도하게 지체하도록 할 수 있는 난류가 발생함을 보여준다.

• 한국압력기기공학회 논문집
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• 제12권1호
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• pp.78-84
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• 2016

The FHX (Forced-draft sodium-to-air Heat Exchanger) employed in the ADHRS (active decay heat removal system) is a shell-and-tube type counter-current flow heat exchanger with M-shape finned-tube arrangement. Liquid sodium flows inside the heat transfer tubes and atmospheric air flows over the finned tubes. The unit is placed in the upper region of the reactor building and has function of dumping the system heat load into the final heat sink, i.e., the atmosphere. Heat is transmitted from the primary cold sodium pool into the ADHRS sodium loop via DHX (decay heat exchanger), and a direct heat exchange occurs between the tube-side sodium and the shell-side air through the FHX tube wall. This paper describes the DHRS and the structural design of the FHX.

• International Journal of Fluid Machinery and Systems
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• 제2권4호
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• pp.375-382
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• 2009

Hydraulic instability associated with pressure fluctuations is a serious problem in hydraulic machinery. Pressure fluctuations are usually a result of a strong vortex created in the centre of a flow at the outlet of a runner. At every radial turbine and also at every single regulating axial turbine, the draft tube vortex appears at part-load operating regimes. The consequences of the vortex developed in the draft tube are very unpleasant pressure pulsation, axial and radial forces and torque fluctuation as well as turbine structure vibration. The consequences of the vortex are transferred upstream and downstream with amplitude and frequency modulation in respect of the turbine operating regime, cavitation conditions and air admitted content. Numerical prediction of the vortex appearance in the design stage is a very important task. The amplitude of the pressure pulsation is different for each operating regime therefore the main goal of this research was to numerically predict pressure pulsation amplitude versus different guide vane openings and to compare the results with experimental ones. For the numerical flow analysis of a complete Francis turbine (FT), the computer code ANSYS-CFX11 has been used.