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Labyrinth seals as a type of non-contact seal have been used very often in gas turbine and in many kind of fluid machines. They have various type of shapes. Most of them had been designed from the view point of very practical use and it is difficult to explain their characteristics. However, one of the fundamental design policies of labyrinth seal is to design the configuration which can produce larger differential leakage in the direction of fluid flow. Especially, if there is a periodical variation of pressure difference between both sides of labyrinth seal or there is reciprocal pressure difference, it is very significant in the seal performance to have large difference of leakage in the direction of flow. In this research work, variation of leakage and fluid resistance depending on the flow direction were investigated for the narrow flow path.

Leak and seal performances in stationary state and rotating state for each brush mounted labyrinth and ordinary labyrinth were studied and presented hereunder in this paper. It was found in this research work that seal performance of brushmounted labyrinth is much better than that of ordinary labyrinth. Brush mounted labyrinth has two remarkable characteristics: In the case that the brush is positioned behind fin against flow, i.e. positioned downstream of fin, amount of leakage is suppressed as increasing of rotation speed. In the case that brush is positioned upstream of fin, leakage increases as increasing of rotation speed.