Kja. Westin et al., EXPERIMENTS IN A BOUNDARY-LAYER SUBJECTED TO FREE-STREAM TURBULENCE .1. BOUNDARY-LAYER STRUCTURE AND RECEPTIVITY, Journal of Fluid Mechanics, 281, 1994, pp. 193-218
The modification of the mean and fluctuating characteristics of a flat
-plate boundary layer subjected to nearly isotropic free stream turbul
ence (FST) is studied experimentally using hot-wire anemometry. The st
udy is focused on the region upstream of the transition onset, where t
he fluctuations inside the boundary layer are dominated by elongated f
low structures which grow downstream both in amplitude and length. The
ir downstream development and scaling are investigated, and the result
s are compared with those obtained by previous authors. This allows so
me conclusions about the parameters which are relevant for the modelli
ng 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).