Microjet Configuration Sensitivities for Active Flow Control on Multi-Element High-Lift Systems

Various characteristics of small surface-normal jets (microjets) located on a flap's pressure-side near the trailing edge are investigated as an active aerodynamic load control technology for multi-element high-lift systems. Two-dimensional computational studies are carried out to investigate the sensitivity of microjet aerodynamic effectiveness to configuration. Initially, the effects of microjet location and width are explored. The study shows that lift enhancement decreases as the microjet is moved forward from the trailing edge, and that wider microjets are more effective in lift enhancement and drag reduction, whereas thinner microjets are more efficient. Microjet exit velocity profile effect on the integrated forces is also studied, and the effects are shown to be insignificant. To gain preliminary insight of the microjet system requirements, several plenum configurations are studied, and a preliminary analysis of the power requirements to supply the air mass flow is presented. Next, the study is extended to a geometry with moderate trailing edge separation to demonstrate microjet's separation mitigation capability. To gain better understanding of the system requirements, pulsed versus continuous microjets are examined, and it is found that pulsed blowing causes a breakdown of the favorable effect of the microjet on the trailing edge flow and therefore reduces the circulation control effectiveness of the microjet.