Abstract

Abstract The installed flow field for a Variable Pitch Fan (VPF) operating in reverse thrust for the complete aircraft landing run is described in this paper. To do this, a VPF design to generate reverse thrust by reversing airflow direction is developed for a representative 40000 lbf modern high bypass ratio engine. Thereafter, to represent the actual flow conditions that the VPF would face, an engine model that includes the nacelle, core inlet splitter, outlet guide vanes, bypass nozzle, core exhaust duct, aft-body plug and core nozzle is designed. The engine model with the VPF is attached to a representative airframe in landing configuration to include the effects of installation. A rolling ground plane that mimics the runway during the landing run is also included to complete the model definition. 3D RANS solutions are carried out for two different VPF stagger angle settings and rotational speeds to obtain the fan flow field. The dynamic installed VPF flow field is characterized by the interaction of the free stream and the reverse stream flows. The two streams meet in a shear layer in the fan passages and get deflected radially outwards before turning back onto themselves. The flow field changes with stagger setting, fan rotational speed and the aircraft landing speed because of the consequent changes in the momentum of the two streams. The description of the installed VPF flow field as generated in this study is necessary to: a) qualify VPF designs that are typically designed by considering only the uninstalled static flow field b) choose the VPF operating setting for different stages of the aircraft landing run.

Highlights

  • In a Variable Pitch Fan (VPF), the pitch setting or stagger angle of the fan blades can be varied by an actuator located in the fan bulletnose

  • To completely describe the installed fan flow field of the VPF in reverse thrust at different landing speeds, the results are presented in the following sequence: 1. The installed configuration differs from the uninstalled configuration in terms of the flow conditions that the VPF will need to operate

  • The change in the fan flow field with change in the landing speed of the aircraft is described by considering the VPF at ζ1 ̊ stagger and N1 fan rotational speed

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Summary

Introduction

In a VPF, the pitch setting or stagger angle of the fan blades can be varied by an actuator located in the fan bulletnose. Such control over the pitch setting can be used to optimize off-design fan operation without the need for a variable area bypass nozzle. The lower mission fuel burn, adaptability to intelligent engine configurations and possibility to mechanically design the system has resulted in research interest in VPF. The combination of ‘slim-line’ nacelle and VPF for reverse thrust without the variable area nozzle and cascade thrust reverser unit can improve the aircraft mission fuel burn in the range of 10 to 15% [6]. The manner in which VPF can be used to generate reverse thrust by changing the direction of airflow is described in Appendix A

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