Design of a two spool contra-rotating turbine for a turbo-fan engine.

Contra-rotating turbines offer enhanced performance over their conventional co-rotating configurations. In addition, vaneless contra-rotating turbine stages offer lesser stage length along with improved performance. Contra-rotating turbines with a vaned LP stages offer a controlled work-split between the stages over a wider range of operating conditions by maintaining inlet swirl to the second rotor. The objective of the present work is to design an equivalent vaned contra-rotating turbine for an existing co-rotating configuration of a two-spool turbo fan engine. The contra-rotating turbine is designed by retaining the existing flow path and HP turbine, and redesigning the LP turbine for fixed radial distributions of inlet total temperature, pressure and swirl. A comparative study between performance of the co-rotating and contra-rotating turbines is carried out for different speeds. Cascade testing of the LP stator and rotor mean sections was carried out to validate the analysis. The LP stage of contra-rotating turbine exhibits a performance improvement by 2% points at design point, as per flow predictions. The reduced flow deflection in stator row is the primary reason for significant reduction in profile and secondary losses in contra-rotating turbine, which contributed to the performance improvement. A significant reduction of 23% in blade weight and 45% in LP stator vane count is obtained