Multi-scale entropy analysis and conditional sampling of the velocity increment in a transitional boundary layer

Boundary layer transition induced by surface imperfections has a great impact on the performance of the long endurance vehicles. A better understanding of the physical mechanism of the transition process would be much helpful in developing new models for transition prediction. The velocity increment is important in the theory of turbulence, but it is rarely discussed in a transitional boundary layer. In this paper, the multi-scale entropy and the conditional sampling are used to study the velocity increment in the boundary layer transition process. Similarities in the distribution of velocity increment in each part (laminar/turbulent) of the intermittent flow are observed. It is also found that there is a process for both the laminar and turbulent part of the fluid motions to evolve into the mature state before the fully developed turbulence is reached.