Interaction of Large-Scale and Small-Scale Oscillations During Separation of a Laminar Boundary Layer

Amplifier and resonator dynamics of a low-Reynolds-number recirculation bubble in a global framework

“…a local characteristic length scale of the base flow. In that respect, the present recirculation bubble should be distinguished from the separation bubbles induced by an adverse pressure gradient on smooth surfaces studied by Gaster (1966); Pauley, Moin & Reynolds (1990) and Haggmark, Bakchinov & Alfredsson (2000), from the recirculation flow behind a bump in the numerical study of Marquillie & Ehrenstein (2003) and from the backward-facing step flow experimentally investigated by Dovgal & Sorokin (2004). For all these flow configurations, the inflow velocity condition is not a Poiseuille profile but a thin boundary layer profile, and the recirculation bubbles are characterized by a displacement thickness of the boundary layer at separation at least 10 times smaller than the recirculation length.…”

Application of flow suction for controlling the shedding of large-scale vortices at boundary-layer separation

“…The coherent vortex motion determined by the global flow properties at the scale of the entire separation region was examined experimentally in [9, 10]. One method of controlling flow separation in such a regime of instability was considered in [11], where vortex formation was found to depend on weak harmonic excitation of the flow in the frequency range of amplifying small perturbations of the separated boundary layer.A possible method of affecting the shedding of periodic vortices used in the present work is flow suction, which is a well-known flow-control technique, in particular, for modification of the transition to turbulence initiated by flow instability behind the boundary-layer separation point [5].Experimental Technique. The experiments were performed in a T-324 low-turbulent subsonic wind tunnel located at the Institute of Theoretical and Applied Mechanics of the Siberian Division of the Russian Academy of Sciences.…”

“…The coherent vortex motion determined by the global flow properties at the scale of the entire separation region was examined experimentally in [9,10]. One method of controlling flow separation in such a regime of instability was considered in [11], where vortex formation was found to depend on weak harmonic excitation of the flow in the frequency range of amplifying small perturbations of the separated boundary layer.…”

“…The experimental model schematically shown in Fig. 1 was previously used to study the formation of coherent vortices in the flow behind a rectangular step on a flat-plate surface [9][10][11]. The model consisting of two plates was mounted in the centerplane of the wind-tunnel test section at a zero angle of attack, and the level of background fluctuations of the boundary layer ahead of the step of height h = 2. coordinate stands for the streamwise distance from the step, and the y coordinate is measured normal to the wall from the surface of the rear plate.…”

“…7), can be assumed to stabilize the latter with respect to shedding of large-scale vortices. In this sense, the control method discussed is similar to that used in the experiments of [11], where the diminution of the separation region and a modification of vortex motion were reached by generation of instability waves of the separated boundary layer. This work was supported by the Ministry of Education and Science of the Russian Federation (Grant No.…”