Aerodynamic investigations on generic fan-in-wing configurations

The present study focuses on the aerodynamic characteristics of generic fan-in-wing configurations based on a combination of numerical simulations and experimental investigations. The objective is to reproduce a transition flight or a Short Take-Off and Landing situation without ground effect. The predictive capabilities of Computational Fluid Dynamics methods are assessed by comparison with experimental data. The obtained experimental data include force measurements, surface pressure measurements, flow field mapping using Stereo-Particle Image Velocimetry, hot-wire measurements and flow visualizations. A variety of wind tunnel model arrangements are tested to analyze the flow physics and the aerodynamic performance of the wing. A structured mesh with minimum geometrical approximations is used to perform Unsteady Reynolds Averaged Navier-Stokes simulations of a configuration with one fan installed in the wing’s rear part. The area surrounding the rotor blades is set up as sliding mesh to simulate the rotation. Time-averaged unsteady results exhibit a satisfactory agreement with the experimental data. Fan-in-wing configurations feature a complex flow field. On the wing upper side, the fan is subject to inlet distortion resulting in a significant dynamic blade loading. On the wing lower side, the jet created by the fan is deflected by the incoming crossflow and rolls-up into a pair of counter-rotating vortices which affect primarily the aerodynamic characteristics of the wing. The flow field of the wing lower side is highly unsteady and creates to some extent a wing dynamic loading. Strong pressure fluctuations are concentrated near the fan inlet and the nozzle. They decay significantly on the outboard wing part. The fan-in-wing flow topology is reported in detail based on experimental data, time-averaged and unsteady numerical simulation results. Furthermore, an extensive parameter study is carried out on generic fan-in-wing configurations of regional aircraft wing planform by means of steady-state actuator disk simulations. The present actuator disk approach is validated against the experimental data. Relevant design parameters are examined including the fan location on the wing, the fan diameter, the fan axis inclination, the ratio of freestream velocity to jet velocity and the angle of attack. In particular, the induced lift caused by a jet flap effect can be maximized by installing the fan near the wing trailing edge. Depending on the velocity ratio, significant drag can be generated at the fan inlet due to the deflection of the incoming cross-flow. The design of an inlet lip with variable radius and a configuration with tangential blowing constitute passive and active lip-flow control solutions, respectively, to reduce the fan inlet distortion originating from boundary layer separation on the inlet lip.