Development of a Research Model to Study the Operability of a Variable Pitch Fan Aero Engine In Reverse Thrust

Abstract

A rationale for the level of model fidelity required to provide the most representative flow field information to ascertain the feasibility of using a Variable Pitch Fan (VPF) in a modern high bypass ratio aero engine to generate reverse thrust is described in this paper. This is done by comparing the 3D RANS flow field solution for a newly developed reverse flow VPF design from two research models: i) isolated engine model in which the bypass duct, guide vanes, splitter and VPF are wrapped in an axisymmetric nacelle and placed in a generic far-field domain and b) integrated model in which the engine is installed to an airframe in landing configuration through a pylon and placed in a far-field domain bound by a rolling runway. The flow field solution obtained at an aircraft landing speed of 80 knots indicates that even though both models can predict the general flow patterns, there are substantial differences in parameters such as the amount of reverse stream, circumferential distribution of flow properties and flow development downstream of the engine. These differences impact the levels of reverse thrust generated, flow distortion entering the core engine and resultant airframe forces. This study makes the case that it is necessary to use an integrated model that includes a full engine nacelle installed on an airframe, to answer design questions for engineering the VPF system to generate reverse thrust.

On the Use of an Inflatable Rubber Lip to Improve the Reverse Thrust Flow Field in a Variable Pitch Fan

“…Solver residual monitoring tolerance and statistical evolution of parameters of interest over a fixed iteration interval is considered to determine the convergence and obtain the reverse thrust flow field vector solution space for the complete aircraft landing run. The detailed description of the model development, computational discretization methods, flow solution methodology and the rationale for utilization of the complex integrated model are discussed in the model development and installed fan flow field description work published by the authors [11,13].…”

“…An integrated airframe-engine-VPF research model that features a reverse flow capable VPF design in a future high bypass ratio geared turbofan engine and installed onto an appropriate twin engine airframe is developed to explore the installed VPF reverse thrust flow field during the aircraft landing run [13]. In order to appropriately resolve the VPF reverse thrust flow field in realistic conditions, a translating ground plane to mimic the rolling runway during the landing run is defined as the base of a large cuboidal far field domain within which a symmetric half of the airframe-engine model with the VPF in reverse thrust is placed, as shown in Figure 1.…”

“…the realistic dynamic installed reverse thrust behavior using flow solutions obtained from an integrated airframe-engine research model [11][12][13]. The installed reverse thrust behavior was obtained by considering the VPF operating in a baseline representative unmodified aircraft-engine configuration without any flared nozzle 'exlets' as in the outdoor engine tests.…”

Estimation of Resultant Airframe Forces for a Variable Pitch Fan Operating in Reverse Thrust Mode

“…The integrated airframe-engine-VPF model is built in this manner to quantify the amount of the decelerating force that a reverse thrust VPF would generate during the landing run of a typical modern airframe installed with a future high bypass ratio turbofan engine and no additional reverse thrust specific design features. Further details of the VPF turbomachinery design, engine components and airframe design, along with a detailed exploration into the benefits of using an integrated model for VPF reverse thrust studies are discussed in a separate model development paper by the authors [11]. [12] GTP-22-1306, RAJENDRAN 6…”

“…While these explorations have resulted in the capability to develop reverse flow VPF turbomachinery designs and validated the concept of establishing reverse flow in an isolated static engine, no studies have thence been done to understand the VPF reverse thrust behavior, as installed on to an airframe during the aircraft landing run. Therefore, to address this research gap, the authors developed an integrated airframe-engine-VPF model to computationally obtain the realistic installed dynamic VPF reverse thrust behavior during the aircraft landing run [11]. Several aspects of the VPF reverse thrust behavior like the installed dynamic fan flow field, distortion transferred on to the core engine inlet during reverse thrust operation and the use of an inflatable rubber lip to improve the reverse flow were discussed by the authors in separate publications [12][13][14].…”