Unsteady Wing-Pylon-Nacelle Interference in Transonic Flow

The interference effects between an unswept supercritical airfoil model and an annular wing representing an engine nacelle were investigated. The investigation aims to better understand and predict the impact of the interence effects on the aeroelastic stability of large, modern transport aircraft at transonic speeds. The main objective was to identify potential aerodynamic instabilities in the interference region due to unsteady shock-wave/boundary-layer interactions. The applied model allows to roll and yaw th nacell relative to the model wing and to pitch the entire model. The aerodynamic response to these movements affects the aeroelastic stability of an aircraft and was also investigated here. The overlap between the wing and the nacelle, and the height of the pylon were designed by numerical simulations such as that locally supersonic velocities and flow separation in the interference region might occur. Two linear hydraulic jacks inside the model were used to perform prescribed yaw and roll movements of the nacelle including the pylon. The experiments were conducted up to Mach numbers of 0.84 in an adaptive solid-wall wind tunnel using a hydraulic driven pitch-oscillation setup. Boundary-layer transition was tripped on the wing as well as on the nacelle. The unsteady tests reveal a strong dependency of the aerodynamic response to the structural movement on the topology of the time-averaged flow field. During the static tests, an aerodynamic instability was detected for certain Mach-number/model-incidence combinations. In addition to the initial objectives, a simple countermeasurement was applied in the interference region and its effectiveness was demonstrated.