Steam Turbine Exhaust Hood With Swirl Flow Separation Ducts

Abstract

The efficiency of a steam turbine is significantly influenced by pressure recovery performance of its low-pressure exhaust hood; hence it is important to specify the cause of loss generation and to devise improved structures. The performance of the exhaust hood is greatly influenced by many structural factors such as the size of its outer casing, design of the diffuser parts and arrangement of internal supports. Previously we optimized an exhaust hood using CFD. However, even for this exhaust hood, large and strong swirl flow was still observed and it seemed to be one of the main causes of the mixing loss. The vortex structure of the exhaust hood flow was carefully examined for this reason, and swirls with a strong vorticity were all found to originate from the upper part of the exhaust hood for all models calculated. In the present study, we propose a new structure with special ducts capable of effectively decreasing the swirl strength. Then, we experimentally verify the effectiveness of the improved structure and confirm the possibility of further performance enhancement.