The Mechanisms of the Phenomenon of Tornado-Like Jets Self-Organization in the Flow Along the Dimples on the Initially Flat Surface

Abstract

The mechanisms of the phenomenon of the tornado-like jets self-organization are described. Tornado-like jets are incorporated into a continuous medium stream and induced by three-dimensional reliefs of double curvature indented on surfaces.

A review of turbulent skin-friction drag reduction by near-wall transverse forcing

“…The drag-reduction properties of dimples was first suggested by researchers at the Kurchatov Institute of Atomic Energy in Russia [Kiknadze et al, 1984]. They later also advanced hypotheses on the physical mechanism behind these surface modifications, such as the creation of streamwise "tornado-like" vortical structures, and explored practical applications, such as large dimples over the surface of a high speed train [Kiknadze et al, 2009[Kiknadze et al, , 2012 (refer also to Blood [1995] for further possible applications on other transport vehicles). The drag-reduction margins reported by this group are the largest ever reported for dimples, namely 20% by Alekseev et al [1998], 17% by Kiknadze et al [2006], and 15% by Kiknadze et al [2009], although insufficient details on the methodology and the uncertainty of the overall measured drag-reduction levels were given in order to assess the validity and reproducibility of these experimental campaigns.…”

Dimples for Skin-Friction Drag Reduction: Status and Perspectives

“…The first attempt at explaining drag reduction by dimples is from Kiknadze et al [32], who based their explanations uniquely on video records and photographs, even though similar observations were already put forward in previous numerical [16] and experimental [28] studies. According to ref.…”

“…According to ref. [32], whose authors are affiliated with the Research and Production Centre "Tornado-Like Jet Technologies" in Moscow, the action of dimples can be explained by a so-called tornado-like jet self-organization. In plain words, this is how the flow organizes itself and develops over the double-curvature concavity of a dimple.…”