Analytical and experimental investigations into hybrid laminar flow control (HLFC)

A transition control methodology using hybrid laminar flow control (HLFC) for drag reduction for civil transport aircraft is described. An HLFC concept with a single suction chamber with varying porosity can be integrated into the leading-edge wing structure, with the wing ice protection system and high lift system. The resultant structural system is less complex than the multi-chamber concept, and with weight saving. A turbulent type of pressure distribution has been applied to a civil transport retrofit HLFC wing design resulted with a higher aerodynamic performance than a favourable gradient type of pressure distribution. A turbulent type of pressure distribution also has the potential of being able to retain the performance of a conventional aircraft in the case of suction system failure. An analysis of wind tunnel transition data with linear stability analysis method is described. Detailed measurements of the tunnel environment and fluctuations within the boundary layer are required to provide a better understanding of the physics of transition and data for non-linear methods. A wind tunnel testing capability developed for measuring the effect of small features on transition in natural laminar flow could be extended to HLFC to investigate the effect of suction on the disturbances due to various degree of surface imperfections. A high Reynolds number wind tunnel simulation technique using surface suction to thin the turbulent boundary layer has been demonstrated theoretically and experimentally for a turbulent flow wing design. A theoretical investigation has shown that this technique could be extended to an aircraft with a HLFC wing design.