NUMERICAL SIMULATION OF TWIN SPOOL AXIAL FLOW TURBINES OF A SMALL GAS TURBINE ENGINE

Reynolds Averaged Navier-Stokes CFD analysis is carried out for a twin spool turbine of a typical small gas turbine engine, using commercial CFD solvers by employing SST turbulence model to understand the 3D flow field. In this work, detailed performance characterization at design and off-design speeds of both the high pressure (HP) and the low pressure (LP) stages is carried out using two approaches. In the First approach, individual HP and LP turbine stages are analyzed separately (case 1) with well-defined inlet and outlet boundary conditions and, in the second approach HP and LP turbine stages are analyzed together (case 2). NUMECA-AutoGrid is used to generate a good quality mesh with y(+) around one. RANS CFD simulations are carried out for design speed, using both ANSYS-CFX and NUMEECA's FINE/Turbo solver and compared for conformity of the CFD analysis results. Further ANSYS-CFX is used for the detailed flow simulations for design and off-design speeds. The turbine parameters such as mass flow function, specific work function and total-to-total adiabatic efficiency of the HP and LP turbines are compared for case 1 and case 2. From case 1 & case 2 analysis, it is observed that, LP turbine stage is capable of allowing higher mass flow than required, but HP turbine stage limits the mass flow. Cascade testing of HP turbine mean section profiles has been carried out and compared with CFD analysis results.