Experimental study of a Λ-structure development and its transformation into the turbulent spot
Artikel i vetenskaplig tidskrift, 2000

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

Författare

G.R. Grek

V.V. Kozlov

M.M. Katasonov

Valery Chernoray

Chalmers, Tillämpad mekanik

Current Science

0011-3891 (ISSN)

Vol. 79 781-789

Ämneskategorier

Strömningsmekanik och akustik