On Nature of K-Breakdown of a Laminar Boundary Layer. New Experimental Data

Abstract

The detailed analysis of nonlinear breakdown of a laminar boundary layer had been carried out in the fundamental experimental work [1]. The results of this work (a strong amplification of three-dimensionality, a sudden appearance of “spikes” and high frequency oscillations etc.) are discussed and analyzed with the unremitting interest. The work [1] remains a base for theoretical models up to the present time. For a long time the general opinion was that the discovered in [1] sequence of nonlinear processes leading to breakdown of a laminar regime has been the inherent property of the boundary layer flow. However, a new type of a laminar-turbulent transition in a boundary layer which differs from classical K-breakdown [1] in principle, had been discovered in 1976, [2]. The main features of this type of transition were the generation of the subharmonic oscillation and a packet of low frequency disturbances with subsequent nonlinear interaction of different modes of disturbances. This subharmonic type of transition was studied in subsequent experiments [3]–[6]. The theory of subharmonic activity of distrubances is developed in [7]–[8]. It was established in [3] that the subharmonic resonant three-wave interaction is the man mechanism leading to this way of transition. Possible causes of the realization of either type of transition are also discussed in [3].