THROUGH FLOW FLANGE-TO-FLANGE TURBINE & DIFFUSER ANALYSIS

At the present time an important aspect of power generation in combined cycle power plants is to keep part load performance of heavy duty gas turbines sufficiently high. Therefore it is a matter of importance to ensure the aerodynamic alignment between the turbine and exhaust diffuser, allowing potential increase in both turbine efficiency and diffuser pressure recovery. The benefit of such alignment could be noticed at numerical analysis accuracy of part-load conditions in particular due to the change in gas flow angle downstream of the turbine and resulting in an incidence on the diffuser struts. This incidence, in its turn, often causes local flow separation and an associated loss increase. This paper presents an integrated approach of the turbine and diffuser aerodynamic design by means of use of a single 3D Navier-Stokes CFD model. This model explores an automatic interface between the turbine and diffuser calculation domains. Furthermore, whilst gas turbine part load performance has been improved thanks to last stage turbine blade redesign, the above-mentioned integrated turbine & diffuser numerical modelling was used as working instrument to reach the optimal solution in terms of flange-to-flange efficiency in a broad operation range. Following test results, comparison against the numerical prediction fully proved the validity of chosen analytical approach.