Andrey Bakchinov

Experimental study of the K-regime of breakdown in straight and swept wing boundary layers

~Received 16 October 2000; accepted 28 February 2001!In this Brief Communication, the nonlinear evolution of periodical disturbances generated by anexternal sound field in a swept wing boundary layer is presented. All experimental results arecompared with corresponding data for a straight wing configuration. The Tollmien–Schlichtinginstability has been studied, and it was found that the disturbance flow field remained highlydeterministic and periodic in both time and space until the latest stages of the transition. Afrequency-wave number Fourier analysis shows that the disturbance spectra comprise only thefundamental wave and its higher harmonics. The K-type breakdown scenario was observed, and thenonsymmetry of flow patterns in the swept wing boundary layer was found to be due to the presenceof the cross flow.

A multi-sensor hot-wire anemometer system for investigation of wall-bounded flow structures

This work describes a hot-wire anemometer system and an experimental procedure designed for mapping of the flow structure in disturbed boundary layers. It also briefly presents results from periodically disturbed wing boundary layers. The hot-wire system consists of a number of individual anemometer units, which can be combined to operate multi-sensor probes for simultaneous measurement of velocities in many points. In the present paper, however, only a single probe was used mounted in a dedicated traverse system in order to demonstrate how ensemble averaging can provide knowledge about the growth and decay of organised flow structures, as long as they are periodic in both time and space. The information from this flow structure can then be used in the design of multi-array hot-wire probes for further studies of the non-deterministic stages of the boundary layer transition.