A variable pitch fan and ultrahigh bypass ratio turbofans - A conceptual evaluation

摘要

This paper presents a short summary of the evaluation of the implementation, in a future large long range ultrahigh bypass ratio turbofan, of a Variable Pitch Fan VPF and, variable low pressure turbine nozzle guide vanes LPT NGVs, aiming to improve the overall engine efficiency and, consequently to improve the specific fuel consumption. It represents a small part of the work carried out in the ENOVAL European project. The work carried out includes: a) a model to predict fan pressure ratio performance map when varying the fan pitch angle, model validated with experimental data and, also b) some considerations on outer fan and inner fan performance predictions from the fan map, as well as on c) the low pressure turbine performance with variable nozzle guide vanes. Attending to Variable Pitch Fan efficiency performance map, two extreme cases have considered in the study: case 1, where it is assumed that the efficiency of the VPF does not change with the fan pitch angle and, case 2 where an experimental efficiency correlation with the fan pitch angle is assumed. Finally, the paper presents an advance of the most relevant engine results for midcruise flight condition consequence of these concepts implementation in the baseline engine, the ENOVAL ELLRT. All the results are referred to the respective baseline engine variables at the respective flight condition. At midcruise, the paper shows that significant benefits on specific fuel consumption seems to be achievable, depending on fan pitch angle, LPT NGVs position, and case 1 or case 2.