Effects of location, shape and width of a suction slot on the water removal performance of a hollow stator blade

Abstract

Experimental tests were implemented on a wet steam test rig to investigate the effects of location, shape and width of a suction slot on the water removal performance of a hollow stator blade. A straight cascade with varying outlet Mach numbers and suction pressure differences was used for the tests. The inlet flow conditions were consistent with the real running condition before the last stage stator of a 1000-MW nuclear steam turbine. Results show that the flow Mach number and suction pressure difference affect the amount of water removed. A moderate increase in the suction pressure difference triggers water film vaporisation, which decreases water removal performance. The amount of water removed continuously increases, as the slot location moves from 0.24 to 0.42 times the axial chord in the suction surface. Compared with the straight slot, the step-shaped slot cannot improve the water removal performance. On the contrary, the result is poor when the Mach number is above 0.7 because additional sharp corner leads to more serious water vaporisation. A suction slot with an arc-shaped inlet significantly improves the water removal performance by eliminating water film vaporisation under the test conditions. A 0.35-mm-width suction slot is apt to allow water film across, and a 2-mm-width suction slot cannot form an effective suction pressure difference along the slot height, both leading to poor water removal performance. Meanwhile, 0.7- and 1-mm-width suction slots promote good water removal performance, but the latter is less affected by water vaporisation.