Influence of high-amplitude noise on boundary-layer transition to turbulence

1998 by the American Institute of Aeronautics and Astronautics Inc. All rights reserved. This work continues detailed experiments of boundary layers undergoing transition to turbulence with the major effort directed toward the most important issue facing the understanding of fundamental causes of transition, i.e., the receptivity to freestream disturbances. This problem is reviewed in detail by Saric et al. (1994). The present effort concentrates on leading-edge receptivity and receptivity of two-dimensional roughness. The effects of large-amplitude freestream noise is considered with the effort directed toward determining the limits of linear receptivity. Single-frequency and broad-band sound waves are used along with 2-D roughness elements to determine how the unstable waves are initiated. New data are presented on leading edge-receptivity that clarify some difficulties with previous experimental work. Comparisons with recent DNS are excellent. Data are also presented for nonlinear receptivity of 2-D roughness elements. It is shown that there is little difference between the single-frequency excitation and white noise in that the response is still keenly triggered by the amplitude of the individual mode. Thus a single frequency at 120 dB is more dangerous than white noise at 120 dB where the energy is distributed of many modes.

Influence of high-amplitude noise on boundary-layer transition to turbulence Conference Paper