Through this study, velocity distribution characteristics of exit section and downstream straight length of square sectional 180° and 90° curved ducts were numerically analyzed with RSM (Reynolds Stress Model) by changing various flow parameters such as air velocity, surface roughness and hydraulic diameter etc. As a result of it, the maximum velocity profiles according to air velocity in 180° and 90° curved ducts were indicated at Y/D=0.8 and X/D=0.7 region. Also, the efficient measuring location in bended duct downstream was able to suggest when the most stable straight duct length in flow deviations were indicated at L/D=30 and L/D=10 region, and the standard deviation characteristics according to hydraulic diameter were mostly indicated at L/D=15∼30 and L/D=10 region considering minimum deviations in the same velocity condition.

The schedule speed is one of the most important elements of railway industry. In korea, Gyeongbu Line’s highest speed is 300km/h. But it’s schedule-speed is no more than about 174km/h from Seoul to Busan. In this study, we analyzed the effect of the proposed improvements in the speed reduction zone using Train Performance Simulation. We found that the improvements can raise the schedule speed from 15 to 20%.