Separation Control for Aeroengine Intakes, Part 1: Low-Speed Investigation of Control Strategies

This paper documents the first part of an investigation into control of the separation occurring over the windward lip of an aeroengine intake operating in a crosswind. The results presented are for a low-speed experimental study that investigated the effectiveness of two candidate control techniques: boundary-layer trips and vortex generator jets. The study was conducted using a novel experimental rig that was designed to set up a representative pressure gradient on a two-dimensional intake lip, and which allowed the experiments to be conducted at a larger scale than would otherwise be possible with the available wind tunnel. It was shown that the rig exhibited the same typical flow behaviors as a three-dimensional intake operating at low engine mass flow (low fan-face Mach number) under crosswind conditions. Control techniques were applied to reduce the separation on the intake lip, and consequently reduce the distortion in total pressure at the fan face. Both boundary-layer trips and vortex generator jets positioned on the outside surface of the intake lip were found to successfully remove the leading-edge separation. A combination of vortex generator jets outside and inside the intake further reduced the distortion in total pressure.