Origin of Turbulence in Near-Wall Flows

Abstract

The origin of turbulence in fluids is a long-standing problem being in focus of researches through decades due to its great importance in a variety of engineering applications. Meanwhile, the study of turbulence origin is a part of the fundamental physical problem of the turbulence description and the philosophical problem of determinism and chaos. This paper is concern to a review of new findings in the field of laminar-turbulent transition of near-wall flows.

Parametric study of separation and transition characteristics over an airfoil at low Reynolds numbers

“…However, for a J 6 ; the separation bubble forms near the leading edge and causes a can provide further insight. Transition in a separated shear layer exposed to low magnitude free-stream disturbances proceeds by the amplification of background velocity and pressure fluctuations over a band of unstable frequencies (Dovgal et al 1994;Boiko et al 2002). The ability to estimate or measure this frequency band is important in low Reynolds number active flow control systems that target these frequencies acoustically or mechanically to accelerate the transition process (Gad-el-Hak 1990; Nishioka et al 1990;Yarusevych et al 2005;Jones et al 2008).…”

Influence of an unfavourable pressure gradient on the breakdown of boundary layer streaks

“…As is known (Boiko et al, 2002), the laminar breakdown in wall-bounded shear flows is often associated with transverse modulations of a flow by either steady streamwise vortices (e.g., Görtler vortices, crossflow vortices) or unsteady streamwise structures (boundary-layer streaks at high free-stream turbulence, Λ-, Ω-, and hairpin vortices). These structures create spatial velocity modulations providing favourable conditions for appearance of secondary instabilities, which, in turn, promote the flow breakdown and lead to turbulence in such flows.…”

“…The strength of the spanwise and the wall-normal gradients of the streamwise velocity as well as a spacing between the streamwise perturbations are particularly important for the mode selection. Typically, the varicose instability mode prevails during the breakdown of long-wave vortices, whereas the sinusoidal mode is most often observed on short-wave disturbances, see Li and Malik (1995), Bottaro and Klingmann (1996).…”

Three-wave interactions of disturbances in a hypersonic boundary layer on a porous surface

“…It is known that the use of various wavy and porous surfaces, slotted suction, and heated and cooled surfaces substantially affects the character of disturbance development in boundary layers. Possible consequences are, on the one hand, suppression of various disturbances and longer regions of the laminar flow and, on the other hand, intensification of exchange processes and turbulization of the boundary layer (see [1,2]). Therefore, it seems reasonable to examine these factors for the purpose of solving problems of boundary-layer control in practice.…”

“…Both two-dimensional vortex waves with b = 0 (curves 1) and three-dimensional vortex waves with b = ±0.14 (curves 2) are considered in this triplet at the subharmonic frequency. The coefficients |S 1 2,3 | for the acoustic harmonic with F II refer to the solid curves in Fig. 3, and the coefficients |S 2 1,3 | = |S 3 1,2 | for vortex subharmonics refer to the dashed curves in Fig.…”