Experiments in a boundary layer subjected to free stream turbulence. Part 1. Boundary layer structure and receptivity

TLDR

The study focuses on the upstream region of transition onset, where elongated flow structures dominate, and discusses the mechanisms underlying transition, including the role of Tollmien–Schlichting waves, in a companion paper. The authors investigate how nearly isotropic free‑stream turbulence modifies the mean and fluctuating characteristics of a flat‑plate boundary layer using hot‑wire anemometry. They experimentally examine the downstream development and scaling of these structures, comparing the results with previous studies. The comparison yields insights into parameters relevant for modeling the transition process.

Abstract

The modification of the mean and fluctuating characteristics of a flat-plate boundary layer subjected to nearly isotropic free stream turbulence (FST) is studied experimentally using hot-wire anemometry. The study is focussed on the region upstream of the transition onset, where the fluctuations inside the boundary layer are dominated by elongated flow structures which grow downstream both in amplitude and length. Their downstream development and scaling are investigated and the results are compared with those obtained by previous authors. This allows some conclusions about the parameters which are relevant for the modelling of the transition process. The mechanisms underlying the transition process and the relative importance of the Tollmien–Schlichting wave instability in this flow are treated in an accompanying paper (part 2 of the present report).