Session: 01-02 Inlet Distortion and Engine Operability I

Paper Number: 151271

On Runway Foreign Object Ingestion With a Variable Pitch Fan in Reverse Thrust Mode 

A Variable Pitch Fan (VPF) can be used to generate reverse thrust by changing the direction of the airflow ingested by the fan rotor during the landing run. This can lead to significant mission fuel burn benefits of future aircraft as the bulky nacelle based thrust reversers are no longer required. When an aircraft is operating on the ground at low speeds with the thrust reversers deployed, there is a potential for foreign object ingestion (FOI). The description of FOI scenarios and quantification of foreign object debris (FOD) due to ingestion from the runway are key explorations required to evaluate the potential of VPF as the main thrust reversal unit. In addition to the NASA Advanced Ducted Propulsor (ADP) and Quiet Clean Short-haul Efficient Engine (QCSEE) programs, the authors have described the flow field and performance metrics of the VPF as a thrust reverser in an installed aircraft configuration. However, the feasibility of engineering the VPF necessitates insights into possible runway debris ingestion at low aircraft speeds to understand potential risks and ascertain its reverse thrust performance.

Therefore, in this study, the integrated airframe-engine-VPF research model is used to explore FOI scenarios. The model consists of a modern 40000lbf geared high bypass ratio engine with complete representation of the internal bypass nozzle flow path, and a nacelle that is attached to a twin-engine airframe in landing configuration through a pylon; a rolling ground plane to mimic the runway during the aircraft landing run is also included. Runway debris is represented by a particulate phase inside the computational domain. This is modelled by particles that are introduced several meters ahead of the engine on the ground plane. Multiphase simulations are conducted in which steady-state RANS solutions are used to obtain the flow field. FOI is modelled utilising a discrete particle transport method. The two frameworks are solved using a two-way coupling approach where forces from the generated flow field have an influence on the particles’ trajectory and the particles’ displacement affects the flow field as well. Several parametric analyses are undertaken to determine the effect of specific particle properties, such as density, size and irregularity, on the FOI levels.

At the end of the landing run with the reverse thrust pitch VPF being operated at high engine power setting, two FOI mechanisms are identified: 1) at 60 knots, debris are ingested into the engine from the bypass nozzle exit, due to the unique VPF reverse thrust flow field, and follows the reverse stream direction inside the engine. 2) at lower speeds, a ‘horseshoe’ vortex type flow field is formed directly in front of the engine and close to the ground. This affects the particle trajectories that cause some of these to enter the engine from the intake. These ingested particles interact with the fan blades. However, these particles are centrifuged out inside the fan passages and are ejected out with the reverse stream that comes out from the nominal fan inlet. Consequently, none of the ingested particles enter into the core engine. The extent of FOI from the runway is described in terms of the percentage of debris particles on the runway. Moreover, the effect of crucial particle properties of density, size and irregularity to ingestion levels is described in the paper. Several non-linear relationships are observed as well a novel mapping strategy utilizing an adaptation of Stokes number to provide insights into the trends. The outcome from this study provides insights into one of the key aspects of thrust reverser performance that is necessary for the implementation of the VPF in future sustainable aircraft. 

Presenting Author: Dimitrios Vitlaris Cranfield University

Presenting Author Biography: Dimitrios graduated with distinction in his Bachelor's degree in Mechanical Engineering from the University of Western Macedonia. In his final year, he utilised his dual-degree scholarship award and enrolled in the Computational Fluid Dynamics Master's course at Cranfield University. Currently, he is a PhD researcher within the Rolls-Royce University Technology Centre at Cranfield University working on aerodynamic investigations of a high bypass ratio turbofan engine using a Variable Pitch Fan (VPF) in reverse thrust conditions.

Authors:

Dimitrios Vitlaris Cranfield University
David Rajendran Cranfield University
Richard Tunstall Rolls-Royce plc
Barry Moore Rolls-Royce plc
Rory Clarkson Rolls-Royce plc
Vassilios Pachidis Cranfield University