Numerical Analysis and Performance Characterization of a Rear Variable Area Bypass Injector for Variable Cycle Engines

Variable Cycle Engines (VCEs) are a new family of engines that can dynamically modify their thermodynamic cycle to adapt to different flight conditions, being able to offer the efficiency of a high-bypass turbofan at subsonic speeds and the high specific thrust of a turbojet at supersonic speeds. To be able to do this, VCEs include components with variable geometry that regulate airflow and thermal cycle parameters, such as Variable Area Bypass Injector (VABI), Variable Stator Vanes (VSVs), compressor Inlet Guide Vanes (IGVs) and variable area exhaust nozzle. This study focuses on the Rear Variable Area Bypass Injector (Rear VABI), a key component that is the analog of the mixer in traditional turbofans. By adjusting the bypass to core area ratio, the Rear VABI controls the bypass ratio, playing an important role in optimizing engine performance across a wide operational envelope. In this study a Computational Fluid Dynamics (CFD) analysis is performed to gain insights into the aerodynamic characteristics of the Rear VABI and to assess its performance through the evaluation of quantities such as mixing effectiveness, pressure losses and vorticity generation. The objective is to generate a high-fidelity performance map of this component, that can be integrated into a zero dimensional (0-D) engine model to enhance its predictive capabilities on engine performances across the operating envelope. Available experimental data is used to validate the turbulence model used in the simulations. Subsequently, a relevant literature case is reproduced, serving as a basis for developing a custom-designed geometry tailored to the target engine specifications. A Python tool is developed to generate the geometry of the component ensuring consistency between the high-fidelity CAD model and the system-level engine representation. For this geometry, performance maps have been generated, representing relevant performance parameters as functions of outlet static pressure to total core pressure ratio, and total bypass pressure to total core pressure ratio. Ultimately, this work provides a framework for the development of a multi-fidelity engine performance model with improved prediction accuracy.