Experimental investigation of a streaky structure varicose instability in a swept wing boundary layer

Artikel i vetenskaplig tidskrift, 2004

The investigation results of the controlled experiment of a streaky structure varicose instability in a swept wing boundary layer are presented. The picture of a streaky structure spatial evolution and secondary high-frequency disturbances generated on it is obtained using hot-wire measurements. It is shown that exactly a varicose instability is realized. It has been found that the secondary disturbance increases owing to instability of mean velocity distribution on normal to the wall caused by the streaky structure development. The following features of a varicose breakdown of a longitudinal stationary streaky structure are presented: structure modulation in the longitudinal direction by a secondary disturbance frequency, downstream excitation of new streaky structures, formation and development of nonstationary structures localized in space. In contrast to the boundary layer flow of the unswept wing models, where these structures resemble classical horseshoe structures or lambda-vortices, only one vortex remains on a swept wing from the two making the vortex structure because of the crossflow.