Transport aircraft wake influenced by oscillating winglet flaps

The wake vortex development in the near held and extended near field behind a four engined large transport aircraft model fitted with an active winglet is presented. A detailed wind-tunnel investigation is conducted using a half-model focusing on the high-lift case of a typical approach configuration at a Reynolds number of 0.5 × 10⁶ based on the wing mean aerodynamic chord and an angle of attack of 6.5 deg. The flowfield is observed using advanced hotwire anemometry mainly focusing on the crossflow plane at 5.6 spans downstream of the model. Based on the time-dependent velocity components the wake flowfield is analyzed by distributions of mean vorticity, turbulence intensities, and spectral densities. Seven main vortical structures dominating the near-field wing vortex sheet roll up and merge to form the remaining trailing vortex in the extended near field. By the use of oscillating winglet flaps the velocity fluctuations at the core region of the remaining vortex are significantly influenced. Distinct narrowband concentrations of turbulent kinetic energy can be found for the farthest downstream plane documenting the presence of the disturbances generated by the winglet flaps which may result in an amplification of inherent far-field instabilities. The frequencies at which these narrowband energy concentrations occur are, on the one hand, dependent on the oscillation frequency of the winglet flaps; on the other hand, there are also independent energy concentrations within the frequency bands associated with wake instabilities.