Modelling and performance analysis of vaneless counter rotating turbine in gas turbine engines

The objective of this article is to develop a method for 1+1/2 type vaneless counter rotating turbine (VCRT) modelling in gas turbine engines and to analyse the influence of the VCRT on a turbofan engine. By studying the off-design features of the VCRT, a new method to describe the VCRT characteristic map was established. The new turbine maps were integrated into the gas turbine performance simulation model based on component maps. The throttle performance of a low bypass counter rotating turbofan engine was simulated and the results were validated with engine test data. The validation results show that the new method improves the accuracy of the VCRT engine performance simulation. The influence of the VCRT on the engine steady state performance was illuminated by comparing the performance of a VCRT engine with that of a conventional engine. Under low engine load conditions, the insufficient work capacity of the VCRT low pressure turbine was detected due to the decrease of both its efficiency and pressure ratio. Consequently, the VCRT engine’s turbine inlet temperature, fan rotating speed, mass flow rate and engine thrust decreased while its specific fuel consumption increased compared to that of a conventional engine.