Laminar flow active/passive control technology

Friction drag is the major part of the total drag of a transport. Reducing the friction drag is essential for improving aircraft performance and its influence on the environment. Since laminar friction drag is much less than the turbulent one, one of the important measures for reducing the friction drag is to increase the laminar flow extent, and if possible, to realize a fully laminar flow. Three types of laminar flow active control technology, including natural laminar flow, fully laminar flow and hybrid laminar flow controls (HLFC), are formed through half centenary reseach. Based on the analysis of drag reduction and instability of flow, the concepts, methods, advantages and disadvantages, potential benefits and design methods of laminar flow control aircraft and its operational maintenance (including protection from insect contamination and ice accumulation) are described systematically in the present paper. The effectiveness and difficulties of active control are shown by briefly introducing the projects of HLFC flight tests of the X21A slotted suction flight tests, simulated airlines flight tests of Jetstar HLFC leading edge systems and Boeing 757 HLFC flight tests. A kind of passive control technology, from its mechanism to the flight demonstrator, is also systematically introduced in the present paper.