A Literature Review of Low Pressure Steam Turbine Exhaust Hood and Diffuser Studies

Abstract

This paper summarizes the findings from research studies carried out over the last 30 years, to better understand the flows in steam turbine low pressure exhaust hoods and diffusers. The work aims to highlight the areas where further study is still required. A detailed description of the flow structure is outlined and the influence of the last turbine stage and the hood geometry on loss coefficient is explored. At present, the key challenge faced is numerically modeling the three-dimensional, unsteady, transonic, wet steam exhaust hood flow given the impractically high computational power requirement. Multiple calculation simplifications to reduce the computational demand have been successfully verified with experimental data, but at present there is no 'best-practice' approach to reduce the computational time for routine design exercises. This paper highlights the importance of coupling the exhaust hood to the last stage steam turbine blades to capture the interaction; ensuring the total pressure and swirl angle profiles, along with the tip leakage jet are accurately applied to the diffuser inlet. The nonaxial symmetry of the exhaust hood means it is also important to model the full blade annulus. More studies have emerged modeling the wet steam and unsteady flow effects, but more work is required in this area to fully understand the impact on the flow structure.

The Experimental Studies of Improving the Aerodynamic Performance of a Turbine Exhaust System

“…The total KE flux was also considered, differing from Eq. (2) in that it incorporates all three velocity components for the KE nonuniformity (Ux, Uy, Uz)…”

“…Burton et al [2] summarized the most recent studies of steam turbine exhaust hood and diffuser performance. Owczarek et al [3], Zhang et al [4], and Yoon et al [5] found that the major sepa ration region appears behind the diffuser casing or the flow guide.…”

An Alternative Numerical Model for Investigating Three- Dimensional Steam Turbine Exhaust Hood

“…This necessitates the use of lowfidelity numerical models to reduce the computational demand to levels suitable for use in industrial design processes over the last two decades. A summary of these methods which couple the turbine last stage and the exhaust hood has been discussed by Burton et al (2013). The simulation of isolated exhaust hood from the last stage blade could drastically reduce the computational power.…”

Effect of Wet Steam on Aerodynamic Performance of Low-Pressure Exhaust Passage with Last Stage Blade

“…For recent years, researches on the aerodynamic performance of exhaust passage focus principally on the structure redesign in such aspects as the flow guide, guiding cone, and built-in guide device (Fan et al 2007 andBurton et al 2013). Among the common methods of providing flow characteristics in the exhaust passage are a full-scale model test (Lagun et al 1984), scale-model experiment (Zhang et al 2007 andVeerabathraswam et al 2016), and numerical investigation (Yoon et al 2002 andMizumi et al 2013).…”