Numerical Investigation of Condenser Pressure Effect on Last Stage Operation of Low Pressure Wet Steam Turbines

The flow in nuclear steam turbines is mainly affected in normal operating conditions by the condenser pressure, which depends on the heat sink temperature variations. This has an effect not only on the performance, but can also lead to undesired flow regimes and become related to safety issues.The flow in the low pressure last stages is characterized by two main features: unsteadiness due to the rotation and asymmetry due to the exhaust hood. The effect of the condenser pressure on the stage flow is numerically analyzed with steady and full unsteady approaches. Three distinct flow regimes can be identified at nominal, low and high condenser pressures with different types of unsteady behavior.A detailed investigation of the steam flow and possible consequences for the turbine safety is carried out at nominal and critical operating points. Comparisons of steady/unsteady approaches and the effect of the hood design are also presented.Copyright © 2013 by ASME