Hiroyuki Kawagishi

Development of Global Optimization Method for Design of Turbine Stages

A new optimization method which can search for the global optimum solution and decrease the number of iterations was developed. The performance of the new method was found to be effective in finding the optimum solution for single- and multi-peaked functions for which the global optimum solution was known in advance. According to the application of the method to the optimum design of turbine stages, it was shown that the method can search the global optimum solution at approximately one seventh of the iterations of GA (Genetic Algorithm) or SA (Simulated Annealing).Copyright

Influence of Surface Roughness on Turbine Nozzle Profile Loss and Secondary Loss

The effects of surface roughness of both nozzle and end-wall on a turbine nozzle performance were investigated experimentally using liner cascade wind tunnel facility under the Reynolds number (Re) condition of Re = 0.3∼1.0 × 106 . With buffing, milling, sand blasting and shot blasting, the total of seven levels of the model surface roughness were realized. In order to clarify the effect of the nozzle surface roughness on the profile loss, total pressure losses were measured using three-hole probe for different levels of the surface roughness. It became clear the nozzle profile loss increases as Reynolds number increases for larger roughness group. In addition, it appeared the profile loss depends on not only maximum value of the surface roughness but also roughness conditions. In order to examine the effect of surface roughness on the secondary flow loss, spatial total pressure field of the secondary flow region was measured using three-hole probe for the cases of smooth or rough nozzle surface with smooth or rough end-wall. The secondary flow structures were recognized at the 5∼10% span-wise height region of the suction surface of the nozzle for all cases. With increasing the nozzle surface roughness, not only the profile loss but also net secondary flow loss increases, which is defined as the difference between the total pressure loss and the profile loss in the secondary flow region. However, increase of the end-wall roughness has higher effect on the net secondary flow loss increase. Difference of the effect between the nozzle surface roughness and the end-wall roughness on the nozzle secondary flow loss was discussed.Copyright

Influence of Wetness on Efficiency of the Full Scale Size Low Pressure Turbines

Efficiencies of 60Hz full size test turbines were measured in various wet steam conditions to reveal the wetness impact on the performance. We changed the wetness and stage load conditions independently under the condition of constant steam mass flow rate in the low pressure turbine. The test results told that the stage efficiency decreases with the increasing of wetness as many studies showed, furthermore, the stage efficiency decreases more in smaller load conditions than in the design point. In addition, blade length effects were examined by comparing two types of LP turbine to be found that the longer case got more deficits at the same wetness. Some theoretical evaluations were tried and a combination of some simple loss models explained the tendencies above, qualitatively. The evaluation showed that absolute value of mechanical wet loss such as braking loss remained unchanged regardless of load conditions, so in low load condition, ratio of mechanical loss to stage load increased, resulting decrease of stage efficiency. It also showed that increasing wet loss at the longer blade was mainly because higher circumferential velocity caused larger mechanical wet loss such as braking loss.Copyright

An Experimental Flow Investigation of Low Pressure Turbine Stages With Various Wet Conditions

Detail flow characteristics of an actual size low pressure steam turbine stages under real operating conditions were examined in this paper. The main purpose of the experimental work was to obtain the radial distribution of the velocity triangles in the wet flow of the large size turbine, so that a series of tests were carried out with various wet conditions. Some particular changes of the flow pattern were observed at the exit of both the stator and the blade rows which would not predicted by steam turbine design tools.A kind of flow coefficient was defined and investigated as well as the steam velocities. With an assumption of the steam wetness distribution along the blade span, a tendency of the flow coefficient was appeared which was similar to previous work [7]. The wetness assumption was qualitatively verified by bore-scope observation of the water concentration on the stator surface and the fog condition of the steam path.Copyright

Evaluation of 1700C Class Turbine Blades in Hydrogen Fueled Combustion Turbine System

This paper describes the cooling design and experimental evaluations of the 1700C class turbine blades in hydrogen fueled combustion turbine system. The hybrid cooling method combining recovery steam cooling with partial film cooling was chosen based on a careful study on several cooling systems from the viewpoint of plant efficiency and durability of turbine blades. In the development process, high temperature cooled turbine blades, the advanced cooling technologies, single crystal super alloy and thermal barrier coating (TBC) are important issues to be paid attention and following experiments were performed. First, outer heat transfer test on stator blade and internal heat transfer test in ribbed channel for cooling rotor blade were carried out using liquid crystal thermography. The cooling effectiveness of rotor blade was further investigated in steam driven wind tunnel. The characteristics of single crystal super alloy and TBC were also evaluated in hot steam environment. As a next step, the scale model test blades of size nearly one half to that of the first stage stator and rotor blades in actual turbine were designed and manufactured. Finally, the turbine blade cascade tests were conducted using hydrogen-oxygen combustion driven wind tunnel under practical hot steam conditions of 1700C and 2.5MPa. In these experiments, cooling effectiveness, metal temperatures and cooling steam flow characteristics were investigated. After completing all the test runs, the robustness of blade substrate and TBC were inspected. The experimental results on the hybrid cooling method and blade design procedures are discussed.© 2000 ASME