Numerical analysis of the performance of a low pressure turbine during an intermediate pressure shaft fail in three-shaft turbofan engines

Abstract

Consulta en la Biblioteca ETSI Industriales (8867)

[EN] Low Pressure Turbine aerodynamics plays a key role during an Intermediate Pressure shaft failure event. The IP Turbine acceleration, together with the High Pressure Compressor surge, lead to high negative incidence angles at the LPT inlet. Such incidences cause a reduction in LPT performance, affecting favourably the limitation of the free running turbine final speed. The objective of the present work is to develop a methodology to obtain the LPT map under different over-speed conditions. In order to do that, the performance of the LPT first stage under different over-speed conditions of the upstream turbine has been studied by means of CFD simulations. Then, a stage stacking technique has been developed. Additionally, a splitting technique has also been implemented. The splitting technique is employed to obtain a ¿virtual¿ stage 2 that simulates the performance of the components downstream of the stage 1. Once the map of the stage 2 is obtained, the stage stacking technique is employed to obtain the LPT map under different over-speed conditions by changing the correspondent deteriorated stage 1 map. The methodology has been applied and it has shown satisfactory results. The outputs are presented in two different ways: as a function of the LPT inlet angle and as function of the upstream turbine non-dimensional rotational speed. The obtained results show that the capacity of the LPT is reduced when the incidence moves to negative values. An interesting fact found is that the stage 1 is not choked at any point simulated. The huge increase in pressure losses across the LPT1-NGV forces a rear stage to choke. Therefore, for the LPT rotational speed simulated, the increase in pressure losses across the NGV prevail over the NGV capacity reduction.