The Infra Rig: Experimental and Numerical Investigation of Fan Intake Interaction Under Cross Wind Conditions

Abstract

The increasing demand for higher propulsive efficiency in future turbofan engines has driven a design trend towards Ultra-High Bypass Ratio (UHBR) engines. This shift presents new aerodynamic challenges, particularly in the fan and intake system, as the nacelle is shortened to mitigate weight penalties associated with larger bypass ratios. To investigate these coupling effects, a novel experimental setup was developed using the INFRa rig (Integrated Nacelle Fan Rig assembly). The INFRa rig, located at the Propulsion Test Facility (PTF) of the Institute of Jet Propulsion and Turbomachinery (IFAS) at TU Braunschweig, enables advanced research in propulsor aerodynamics. With cutting-edge capabilities, including cross wind simulation, the rig is uniquely suited to study the complex dynamics of modern UHBR fans at representative take off conditions. This paper explores the fan-intake coupling in a scaled (1:3) UHBR configuration subjected to cross wind conditions through two experimental setups. The first setup, comprises an aspirated throughflow nacelle, focused on intake performance under cross wind. The second featuring a powered fan stage to represent the bypass system, enabling a comparison between unpowered and powered intake configurations. Comparability is guaranteed by complying with Mach's similarity in the aerodynamic interface plane (AIP). Both setups were exposed to clean and distorted inflow conditions, revealing how the fan extends the separation-free operational range of the intake system. A range of operating points, from low-speed subsonic to transonic flows, and inflow conditions — including cross winds up to 38 knots — were evaluated. cross wind conditions caused a reduction in efficiency and pressure ratio, while time-resolved pressure measurements indicated rotating instabilities. To further investigate, steady simulations were conducted at selected operating points, and a comparison between numerical and experimental results is presented.