Experimental study of mechanism of high-frequency breakdown of Λ-structure
Artikel i vetenskaplig tidskrift, 1999

The paper presents the results of the experimental research of characteristics of Λ-structures development and mechanism of their transformation into the turbulent spots. It was shown that isolated Λ-structure can damp as well as increase downstream and transform into a turbulent spot. According to their structure these types of disturbances are two counter-rotating vortices ("legs" of disturbances) closed by the "head" in the leading edge. The difference of these two types is that Λ-structure that damps is a kind of a hairpin vortex and it does not cross the upper boundary layer edge; the "head" of the increasing Λ-structure crosses the upper boundary layer edge and disturbance obtains the form of the Greek letter Λ. It was defined that Λ-structure increase is connected with the development of the secondary high frequency disturbances on the legs of the structure. The reason of it is probably local transverse velocity gradient ∂u / ∂z on the "legs" of Λ-structure which creates conditions for the secondary disturbances development in it. It was shown that frequency of the secondary disturbance decreases because of continuous extending of a localized disturbance under its propagating downstream. Secondary high frequency breakdown of structures is also observed at their periodical generation.


G.R. Grek

M.M. Katasonov

V.V. Kozlov

Valery Chernoray

Chalmers, Tillämpad mekanik

Thermophysics and Aeromechanics

Vol. 6 427-442


Strömningsmekanik och akustik