[en] The characteristics of dual coaxial jet which composed of inner supersonic nozzle of 26500 in constant expansion rate with 1.91 design Mach number and outer converging one with 40 .deg. C converging angle with the variation of outer nozzle stagnation pressure are experimentally investigated in this paper. In which the stagnation pressure for the inner supersonic nozzle is 750kPa thus, the inner jet leaving the nozzle is slightly underexpanded. The plenum pressure of outer nozzle are varied from 200 to 600kPa. Flow visualizations by shadowgraph method, impact pressure and centerline static pressure measurements of dual coaxial jet are presented. The results show that the presence of outer jet affects significantly the structures and pressure distributions of inner jet. And outer jet causes Mach disk which does not appear for the case of single jet stream. As the stagnation pressure of outer jet increases, impact pressure undulation is severe, but the average impact pressure keeps high far downstream

[en] A detailed time dependent behaviour of an unsteady shock wave through the T-type branched duct is investigated with both numerical and experimental methods. In order to study the effect of initial shock Mach number, M_s and the geometry of the duct on the unsteady shock motion, unsteady two-dimensional Navier-Stokes equations are solved by upwind scheme. The complicated flow fields including incident and reflected shock waves, vortex and expansion waves are visualized, and compared with experimented ones. The obtained results show when the shock wave with high initial shock Mach number generates the stronger vortex, increases the strength of reflected shock wave. Furthermore, it is found that the present computational and experimental results are good agreement

[en] Water droplet erosion is one of major concerns in the design of modern large fossil steam turbines because it causes serious operational problems such as performance degradation and reduction of service life. A new erosion model has been developed in the present study for the prediction of water droplet erosion of rotor blades operated in wet steam conditions. The major four erosion parameter; impact velocity, impacting droplet flow rate, droplet size and hardness of target are involved in the model so that it can also be used for engineering purpose at the design stage of rotor blades. Comparison of the predicted erosion rate with the measured data obtained from the practical steam turbine operated for more than 90,000 hours shows good agreement

[en] Hydrogen seal systems of the electricity generator for a nuclear power plant have been analyzed using computational fluid dynamics techniques. The seal system has been operated with two serious problems. The first one is that the seal temperature has been increased progressively, after scheduled overhaul, and the other is that differential pressure between inlet oil and hydrogen has been increased simultaneously. In order to solve these problems, CFD study has been done and results are discussed in this paper. Two types of the seals, flat type and tapered land type, have been compared in terms of force acting on the thrust collar, seal temperature, and oil flow rate. It was found from this study that the flat type seal is not appropriate because the acting force on the collar is not enough to maintain proper oil film thickness and this is main cause of temperature rising occurred in the seal. It has been reported from the operation history that the modified tapered land seal developed from this study shows excellent operating characteristics

[en] In order to investigate the flows with shock wave in branch, 108 deg. elbow and T-junction of the IRWST system of standard Korean nuclear reactor, detail time dependent behaviors of unsteady flow with shock wave, vortex and so on are obtained by numerical method using compressible three-dimensional Navier-Stokes equations. At first, the complex flow including the incident and reflected shock waves, vortex and expansion waves which are generated at the corner of T-junction is calculated by the commercial code of FLUENT6 and is compared with the experimental result to obtain the validation of numerical method. Then the flow fields in above mentioned units are analyzed by numerical method of finite volume method. In numerical analysis, the distributions of flow properties with the moving of shock wave and the forces acting on the wall of each unit which can be used to calculate the size of supporting structure in future are calculated specially. It is found that the initial shock wave of normal type is re-established its type from an oblique one having the same strength of the initial shock wave at the 4 times hydraulic diameters of downstream from the branch point of each unit. Finally, it is turned out that the maximum force acting on the pipe wall becomes in order of the T-junction, 108 .deg. elbow and branch in magnitude, respectively

[en] The In-containment Refueling Water Storage Tank (IRWST) has the function of heat sink when steam is released from the pressurizer. The hydrodynamic behaviors occurring at the sparger are very complex because of the wide variety of operating conditions and the complex geometry. Hydrodynamic behavior when air is discharged through a sparger in a condensation pool is investigated using CFD techniques in the present study. The effect of pressure acting on the sparger header during both water and air discharge through the sparger is studied. In addition, pressure oscillation occurring during air discharge through the sparger is studied for a better understanding of mechanisms of air discharge and a better design of the IRWST, including sparger. (authors)