Experiments were carried out to investigate the seal characteristics of real size models of a typical steppedlabyrinth seal. Flow coefficients of the labyrinth seal were obtained in a high speed experiment facility at different pressure ratios (105－28)

relative sealing clearances (24－40)

Reynolds numbers(1900－28000) and rotational speeds (0－12000r/min).Results indicated that the flow coefficient of labyrinth seal rose with the increase of pressure ratio

and decreased with a higher relative sealing clearance. No noticeable change of flow coefficient was found when the labyrinth seal ran under a rotational speed of 5000r/min. However

under high rotational speed and low pressure ratio conditions

the flow coefficient declined more than 301% as the operating speed went up. Moreover

under the conditions with lower Reynolds numbers

a rapid drop of flow coefficient was found with the decreasing Reynolds numbers. When the Reynolds numbers were larger than 6000

no clear effect on flow coefficients can be observed. Axial pressure distribution measurements showed that pressure drop reached its minimum and maximum values when air flowed through the first and the last seal tooth respectively

the pressure dropped through the remaining teeth were almost uniform. According to the findings

an empirical expression to evaluate flow coefficients of steppedlabyrinth seals was also obtained

and agreed with the experimental results perfectly.