Chang-Goo Kim

A study on the effectiveness of an anti vortex device in the sump model by experiment and CFD

The head-capacity curves of pumps developed by the pump manufacturer are based on tests of a single pump operation in a semi-infinite basin with no closed walls of floors and with no stray currents. Therefore, the flow into the pump intake has no vortices of swirling. However, pump station designers relying on these curves to define the operating conditions for the selected pump sometimes experience reductions in capacity and efficiency, as well as an increase of vibration and additional noise. Therefore, sump model testing is necessary in order to examine the flow structure around intake. In this study, flow uniformity according to the flow distribution in the pump intake channel is examined to find out the cause of vortex occurrence in detail by experiment and CFD. Furthermore, the effectiveness of an anti vortex device for the suppression of the vortex occurrence in a single intake pump sump model has been examined by AVD type. The AVDs used for experimental testing, one of which has the shape of a rectangular bar and the other was a trident shape, are attached at the bottom of pump intake channel just below the bell-mouth. The AVD type for CFD test is in the shape of a trident. The experimental sump model was scaled down by a ratio of 1:8 whereas the CFD sump model was scaled to the actual size.

Experimental and CFD analysis for prediction of vortex and swirl angle in the pump sump station model

Sump model testing is mainly used to check flow conditions around the intake structure. In present paper, numerical simulation with SST turbulence model for a scaled sump model was carried out with air entrainment and two phases for prediction of locations of vortex generation. The sump model used for the CFD and experimental analysis was scaled down by a ratio of 1:10. The experiment was performed in Korea Maritime and Ocean University (KMOU) and the flow conditions around pumps intake structure were investigated. In this study, uniformity of flow distribution in the pump intake channel was examined to find out the specific causes of vortex occurrence. Furthermore, the effectiveness of an Anti Vortex Device (AVD) to suppress the vortex occurrence in a single intake pump sump model was examined. CFD and experimental analysis carried out with and without AVDs produced very similar results. Without the AVDs, the maximum swirl angle obtained for experimental and CFD analysis were 10.9 and 11.3 degree respectively. Similarly, with AVDs, the maximum swirl angle obtained for experimental and CFD analysis was 2.7 and 0.2 degree respectively. So, with reference to the ANSI/HI 98 standard that permits a maximum swirl angle of 5 degree, the use of AVDs in experimental and CFD analysis produced very desirable results which is well within the limit.

Effect of Water Depth on the Performance of a Direct Drive Turbine for Wave Energy Converter

Development of high efficiency turbine with good performance is one of the main topics in the field of developing wave energy converter. For the development and improvement of the turbine performance, the effect of wave condition on the turbine performance should be considered in detail. Also, water depth is an important factor because incident wave power to the turbine is considerably influenced by the wave particle amplitude of motion and the amplitude is closely related with the water depth. Therefore, in this study, the effect of water depth on the performance of a direct drive turbine(DDT) for wave energy converter is investigated using the DDT which is installed in two types of wave channel. The experimental results show that the DDT captures more wave energy under the condition of relatively shallow water depth. When the water depth is shallow, the horizontal water particle amplitude of motion becomes wider and thus, the water power toward the turbine becomes larger.

CFD Analysis for the Performance of Cross-Flow Hydraulic Turbine with the Variation of Blade Angle

The purpose of this study is both to further optimize the structure of cross-flow turbine and to improve the turbine performance. Optimization of the turbine structure has been made by the analysis of the turbine performance with the variation of the blade angle using a commercial CFD code. The results show that inlet and outlet angles of the runner blade give considerable effect on the performance of the turbine. Pressure on the surface of the runner blade changes considerably with the variation of blade angle both at the stages 1 and 2 but relatively small change occurs for the fluid velocity of cross-flow hydraulic turbine. Recirculating flow in the runner passage causes considerable hydraulic loss by which efficiency of the turbine decreases very much.

Determination of Optimum Nozzle Shape of a Direct Drive Turbine by CFD Analysis

The purpose of this study is to examine the influence of nozzle shape on the performance of a direct drive turbine for wave energy converter. The performance of the turbine is calculated by the variation of nozzle shape using a commercial CFD code. The results show that nozzle shape should be designed considering wave height and flow rate entering to the turbine. Best efficiencies of the turbine by 4 types of the nozzle shape do not change largely but overall performances vary mainly by the cross-sectional area of nozzle inlet. The output power of the direct drive turbine changes considerably by the nozzle shape, and a partial region of Stage 2 in the runner blade passage obtain maximum regional output power in comparison with the other region of the runner blade passage.

Experimental Study on a Direct Drive Turbine for Wave Power Converter System

Performance and internal flow of a direct drive turbine (DDT) model for wave power converter system is investigated experimentally. Three kinds of test turbine model are adopted for the examination. Test results show that rotational speed of test runner, differential pressure between front and rear nozzle passages and passage flow rate increase by the increase of wave height and wave period. Maximum output power and best efficiency of the test turbine model locate at the different rotational speed by wave height. Installation of front guide wall and rear water reservoir of the test turbine improves the turbine performance. Large passage vortex occurs both at the front and rear nozzle passages in turn by reciprocating flow in the internal flow passage of the turbine model.