Experimental Investigation of Geometrical Parameters on the Pressure Recovery of Low Pressure Steam Turbine Exhaust Hoods

Abstract

The three-dimensional inhomogeneous flow in the exhaust hoods of low pressure steam turbines is a major cause of losses and the design of low-loss exhaust hoods remains a challenge, particularly in retrofit units. This paper examines the sensitivity of certain geometrical exhaust hood parameters on the pressure recovery of the whole exhaust system of low pressure steam turbines. The experimental investigations are carried out in a scaled exhaust system test rig operating at full-scale Mach numbers and near design flow conditions. The measurements for all exhaust hood configurations have been performed on two axial-radial diffuser geometries at two different load points, which represent the outflow in the design point of a last stage rotor with and without shrouds. The flow measurements make use of pneumatic probes and wall pressure taps. The influence of the exhaust hood area, the flow area in the horizontal joint plane and the location of the steam inlet are examined. The sensitivity of the pressure recovery on these parameters is evaluated. The flow area in the horizontal joint plane is identified as the most sensitive geometrical parameter in the exhaust hood of low pressure steam turbines.