Investigation on low-pressure steam turbine exhaust hood modelling through computational fluid dynamic simulations

The constant growth of renewable energy sources has changed the working condition of the modern power plants, where a greater flexibility of the conventional units is required. Large steam turbines, for instance, have to be capable of partial load operation as well as quick starts in order to ensure a stable functioning of the power grid. This reflects on the design of the steam turbine and in particular on exhaust hoods which have a significant impact on the overall turbine performance, recovering the energy left and therefore affecting the power output. Exhaust hoods have to convert kinetic energy at the turbine last stage exit into static pressure at the condenser by decreasing the flow speed. In axial-radial hoods the flow must turn by 90 degrees in a very short distance, therefore, if such components are not well designed, this may lead to flow separation phenomena which reduce the hood recovery performance. Due to the nowadays operational requirements, it is mandatory to carefully design the steam turbine exhaust system for a wide range of operating conditions, in order to ensure high efficiencies also at partial loads.This work concerns a numerical investigation on a low-pressure steam turbine exhaust hood through computational fluid dynamic simulations, assessing several numerical methods to couple the exhaust casing with the turbine rear stage. The numerical outcomes were compared in terms of flow field distribution and pressure recovery coefficient, by allowing to define a numerical setup which is a good trade-off between results accuracy and computational effort.The constant growth of renewable energy sources has changed the working condition of the modern power plants, where a greater flexibility of the conventional units is required. Large steam turbines, for instance, have to be capable of partial load operation as well as quick starts in order to ensure a stable functioning of the power grid. This reflects on the design of the steam turbine and in particular on exhaust hoods which have a significant impact on the overall turbine performance, recovering the energy left and therefore affecting the power output. Exhaust hoods have to convert kinetic energy at the turbine last stage exit into static pressure at the condenser by decreasing the flow speed. In axial-radial hoods the flow must turn by 90 degrees in a very short distance, therefore, if such components are not well designed, this may lead to flow separation phenomena which reduce the hood recovery performance. Due to the nowadays operational requirements, it is mandatory to carefully design the steam t...