A Comparison of Two Methods for Utilizing Steam Turbine Exhaust Hood Flow Field Data

Abstract

This article describes the effects of two methods for representing the nonuniform distribution of flow properties across a steam turbine discharge annulus, on the hood loss coefficient. One method uses a mass-weighted integration of the property across the station, while the other is based on a mass-derived representative value of the property. The former has the potential for very high accuracy provided a sufficient number of points are integrated. The latter, while less accurate, is easier to apply and therefore more commonly used. The analytical modeling includes a simplistic step profile of pressure across the annulus, as well as a three-dimensional exhaust hood, flow-field simulation calculated using a Navier–Stokes code. Results show that significant errors can occur in the hood loss coefficient with the mass-derived approach. Although the analysis centers on hood loss coefficient as the performance parameter whose sensitivity is being monitored, the results highlight the pitfalls of improper application of measured data for any internal flow system.