Three Dimensional Flow Analysis in a Radial Turbine Rotor. 2nd Report, Flow Field near Tip Clearance and Turbine Efficiency.

Abstract

Three dimensional viscous flow analysis was performed in a radial turbine rotor. Tip clearance area was filled with another computational grid and multi block analysis code was adopted. Clearance height was changed from 0 mm to 1 mm to investigate its influence to leakage flow and turbine efficiency. The results showed that flow field near tip clearance was mainly decided by relation between scraping flow and leakage jet. Leakage mass flow increased greatly at the latter half of rotor passage. Turbine efficiency tended to improve as tip clearance became small. Especially good improvement was found between 0.5 mm and 0.25 mm. It may be cause that scraping flow was dominant at the middle of rotor passage.