Transition prediction methods towards significant drag reduction via laminar flow technology

Efficient and reliable transition prediction methods are of great significance for the development of drag reduction technology through large extension of laminar flow over aircraft. To meet the strong need of engineering design of future laminar aircraft, this article focuses on the development and investigation of three types of transition prediction methods:1) a dual e^N method based on linear stability analysis; 2) a γ-Re_θ model based on localized flow variables; 3) a novel method combining dynamic model decomposition (DMD) and e^N method. These methods are validated by the transition predictions for flows over the DLR-F4 wing-body configuration, the sickle-shaped wing, and the natural-laminar-flow airfoil NLF0416, etc. The results show that the predicted transition points or lines are in good agreement with the experimental data. The dual e^N-method, served as an example of the transition prediction methods, is further demonstrated for aerodynamic design of a natural-laminar-flow wing for short-and medium-range transport aircraft. Remarkable drag reduction has been achieved, which shows that the developed transition prediction methods offer great potential for engineering applications.