Optimal rotor blade swirl law for the last stage of a stationary turbine with an axial diffuser

The flow kinetic-energy conversion into the pressure-forces field in the outlet turbine diffuser increases the heat drop to the last stage, generating additional power. The recovery properties of the diffuser are determined predominantly by the inlet boundary conditions of the flow formed by the last turbine stage. This study aims to demonstrate the influence of the last turbine stage swirl law on the boundary conditions formation at the diffuser inlet. The aerodynamics of the “turbine stage–exhaust diffuser” system (“S–D” system) was studied by an experimental method. The experimental results validated the numerical model of the flow in the “S–D” system. The stage's integral characteristics, the diffuser, and the “S–D” system were obtained for three system geometry variants. The results of the experiments revealed the indisputable advantage of the “negative” swirl law of the last turbine stage. An analysis of the flow structure based on the numerical simulation results revealed the details of the advantages of the boundary conditions at the diffuser inlet formed by the stage with a “negative” swirl compared with the stage with the traditional swirl law. Based on the results, recommendations for the “S–D” system design of powerful stationary gas turbines are proposed.