NUMERICAL SIMULATION OF UNSTEADY FLOW IN LAST STAGE AND EXHAUST HOOD OF A POWERFUL STEAM TURBINE

We have substantiated numerical studies of 3D unsteady turbulent flow in the flow section of the «last stage – exhaust hood» compartment of a powerful steam turbine. We have given the results of numerical simulation of the flow structure in the exhaust hood at normal and doubled radial clearance over the turbine impeller shroud ring for smooth and stepped conjugation of the meridian contours of the stage and the exhaust hood. The influence of the tip back-facing step on the power of the turbine’s last stage and the exhaust hood efficiency is estimated. It is shown that stepped conjugation causes a slight decrease in the stage power at nominal radial clearance. When the radial clearance is doubled, using the step leads to an increase in the power of the stage but twice as small as in the nominal clearance case. The influence of the step on the flow structure and localization of total pressure losses in the exhaust hood is considered.