Abstract: The development of natural laminar flow nacelle is of great significance to enhance the economy and environmental friendliness of modern civil transport aircrafts. The study on the laminar-to-turbulent transition influencing factors of the nacelle can better guide the design of laminar flow nacelle. Based on the linear stability analysis method, the double e^N-method coupled with the RANS equation solver is used to establish an instability prediction method that can simultaneously calculate the N-factors of the induced transition of T-S (Tollmien-Schlichting) wave and cross flow. The method is verified through the spheroid with detailed experimental data. Then the influence factors including flow Mach number, Reynolds number, turbulence, and angle of attack on the transition of the nacelle are examined. The results show that the obvious change of pressure gradient caused by Mach number and angle of attack or sideslip angle will lead to the change of transition position, whereas the Reynolds number and the turbulence intensity have relatively little influence on transition position under high Reynolds number condition, because the range of transition position movement is no more than 5% of the nacelle length. Therefore, in the design stage, it is better to maintain the positive pressure gradient on the upstream of the nacelle as large as possible.

Key words: natural laminar flow nacelle, double e^N method, linear stability analysis, transition judgment, transition influencing factors