UNSTEADY STATOR-ROTOR INTERACTION COUPLED WITH EXHAUST HOOD EFFECT FOR LAST STAGE STEAM TURBINES

Steam turbines behavior assessment is an important issue in the energy industry. Various industrial objectives call for the accurate prediction of turbine steam flow under different operating conditions. Steam turbines' last stages are characterized not only by typical unsteady phenomena due to the rotation, but also by complex subsonic to supersonic flows and asymmetries due to the exhaust. The effect of the exhaust on the last stage performance is analyzed with different simulation methods. The CFD analysis is carried out with several different methodologies using the elsA solver. Steady and unsteady approaches are used for different geometrical configurations: a single inter-blade channel, several inter-blade channels, 360 degrees complete axisymmetric stage and 360 degrees complete stage with exhaust hood. The unsteady models used for the complete stage with exhaust hood show very interesting flow information. The unsteady interactions developing between the turbine rows are coupled with the exhaust effect, strongly affecting the steam flow and the stage performances.