Natural Laminar Flow Wing Development for Future Aircraft Design: Role of Bypass Transition

Natural Laminar Flow Wing Development for
Future Aircraft Design: Role of Bypass Transition

Abstract

For transport aircrafts more than half of total drag is caused by turbulent friction. Natural Laminar Flow (NLF) technology for transport aircraft wing design has come into being after the advent of supercritical airfoils that tries to delay transition. It is currently practiced with the help of semi-empirical models based on linear stability theory. The major problem of NLF design is due to the fact that transition prediction is still not reliable. Experimental validation
of the prediction is even less reliable. In the stability theory attention is focused on finding growing waves as precursor to transition, when the amplitude of these waves grow by empirically fixed factors. Stability approaches disregards role of actual disturbances. Moreover, flow over aircrafts often bypasses this route altogether – as is the case in many other technologically important flows also. Bypass transition is emerging as an important area of research in recent times. In the talk we will discuss about shortcomings of the stability theory and instead talk about receptivity approaches that link theoretically the transition process with specific types of background disturbances. Different types of bypass transition routes, including spatio-temporally growing disturbances would be tracked using receptivity
approach. These will be supplemented by high accuracy computing results for some new wing sections displaying bypass transition. Specific need for studying bypass routes for the design of future transport aircrafts would be discussed.