Journal of Theoretical
and Applied Mechanics

47, 4, pp. 797-814, Warsaw 2009

Influence of the negative and positive jet of wake on laminar-turbulent transition in a boundary layer

Jacek Żabski, Zygmunt Wierciński
In this paper, the results of experimental investigations relating to the influence of negative and positive jet of the wake on laminar-turbulent transition in the boundary layer on a flat plate are described. Using the technique of phase averaging and wavelet analysis, the investigations were carried out in an aerodynamic tunnel with a low level of turbulence in the external stream. The existence of serious differences was noted between the influence of the negative and positive jets due to strong velocity impulses appearing in the area behind the negative jet in the place of the local minimum of the velocity. However, behind the positive jet such strong disturbances appear later, not directly in the region behind the jet. These impulses do not show any signs of chaos and fortuity, therefore they should be rather classified as determined disorder. Moreover, the region of calm behind the positive jet, well-known in the literature, remains also in the area of entirely disturbed flow.
Keywords: laminar-turbulent transition; influence of wakes; flat plate