Simulations of an aircraft with constant and pulsed blowing flow control at the engine/wing junction

In high-lift and especially landing conditions, the vortices emerging from the engine strake and pylon as well as from the inboard and outboard slat tips of civil aircraft configurations can be the cause of the so-called nacelle wake flow separation. This phenomenon might be responsible for the wing stall and sudden lift loss; the effect is expected to increase with the coming up of enlarged nacelles and larger slat cutouts typical of Ultra High Bypass Ratio turbofan engines. In the framework of the European project AFLoNext, DLR and ONERA performed numerical studies focused on a realistic aircraft in high-lift configuration. Structured and unstructured grids were generated to perform Reynolds Averaged Navier-Stokes computations aimed at analyzing the baseline flow without control and determining relevant location and settings for active flow control systems. Constant blowing devices with different slot sizes, types and injection velocities were evaluated with RANS simulations over complete lift polars. The gains in CLmax were quantified; they range from 1 to 3% for actuator capacities compatible with manufacturer requirements, the nacelle wake separation appears at angles of attack one to two degrees higher than without control and the lift levels in post-stall conditions are significantly improved. Finally, unsteady RANS computations were carried out to investigate the potential of a pulsed blowing device. The gains in CLmax and flow separation containment obtained with the latter are similar to those of constant blowing devices which yet exhibit greater momentum coefficient and mass flow rate values.