Experimental Study on Effects of Slot Hot Blowing on Secondary Water Droplet Size and Water Film Thickness

Abstract

The effects of the slot hot blowing of the hollow stator blades on the size of secondary water droplets and the thickness of the water film were experimentally investigated in this paper. The experiment was carried out on the turbine blade cascades in a wet air tunnel with an inlet air wetness fraction of 7.9%, an outlet air velocity of 170 m/s, a slot width of 1.0 mm, and a slot angle of 45 deg to blade surface. The Malvern droplet and particle size analyzer was utilized to measure the secondary water droplet size and distribution downstream of the hollow stator blades in the experimental tests. The experimental results show that the maximum diameter and Sauter mean diameter of the secondary water droplets were reduced greatly, and the water droplet size distribution became narrower. The larger blowing pressure difference resulted in the smaller secondary water droplets and the narrower water droplet size distributions. In addition, the efficiency of water separation from the hollow stator blade surfaces was higher for slot on the suction side than that of the pressure side case. Another simplified experimental test was also carried out on the flat plate to investigate the effect of slot hot blowing on the thickness of the water film downstream of the slot. The conductivity probes were used to measure the thickness of the water film downstream and upstream of the blowing slot. The results show that the slot hot blowing reduced the thickness of the water film downstream of the slot, which was affected by the blowing pressure difference and temperature difference between the hot blowing air and the main airflow. In conclusion, the slot hot blowing of the hollow stator blades has reduced the size of the secondary water droplets and secondarily has evaporated a little water film on the blade surfaces. Both effects are beneficial to reduce the erosion damage to the rotor blades.