This study evaluated the leakage characteristics of a stepped labyrinth seal. Experiments and computational fluid dynamics (CFD) analysis were conducted for a wide range of pressure ratios and clearance sizes, and the effect of the clearance on the leakage characteristics was analyzed by determining the performance of the seal using a dimensionless parameter. It was observed from the analysis that the performance parameter of the seal decreases as the clearance size increases, but it tends to increase when the clearance size exceeds a certain value. In other words, it was revealed that there exists a specific clearance size (S_min) which minimizes the performance parameter of the seal. To identify the cause of this tendency change, a flow analysis was conducted using CFD. It was confirmed that the leakage characteristics of the stepped seal are affected by the size of the cavity, which is the space between the teeth. Therefore, a parametric study was conducted on the design parameters related to the cavity size (tooth height and pitch). The results show that the performance parameter decreases as the tooth height and pitch decreases. Moreover, S_min increases as the tooth height increases and the pitch decreases.

In the vicinity of gas turbine blades, a complex flow field is formed due to the flow separation, reattachment, and secondary flows, and this results in a locally non-uniform and high heat transfer on the surfaces. The present study experimentally investigates the effects of leakage flow through the slot between the gas turbine vane and blade rows on the film cooling effectiveness of the forward region of the shroud ring segment. The experiment is carried out in a linear cascade with five blades. Instead of the vane, a row of rods at the location of the vane trailing edge is installed to consider the wake effect. The leakage flow is introduced through the slot between the vane and blade rows, and additional coolant air is injected from the cooling holes installed at the vane’s outer zone. The effects of the slot geometry, cooling hole configuration, and blowing ratio on the film cooling effectiveness are experimentally investigated using the pressure-sensitive paint (PSP) technique. CO₂ gas and a mixture of SF₆ and N₂ (25% + 75%) are used to simulate the leakage flow to the mainstream density ratios of 1.5 and 2.0, respectively. The results indicate that the area-averaged film cooling effectiveness is affected more by the slot width than by the cooling hole configuration at the same injection conditions, and the lower density ratio cases show higher film cooling effectiveness than the higher density ratio case at the same cooling configuration.

In the vicinity of the gas turbine blades, a complex flow field is formed by various secondary flows, and results in locally non-uniform heat transfer on the surfaces. In particular, the tip leakage flow caused by the pressure difference between the blade pressure side and the suction side is accelerated through the narrow tip clearance, which promotes heat transfer not only at the