Varicose instabilities in turbulent boundary layers (original) (raw)
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Nonlinear sinusoidal and varicose instability in the boundary layer (review)
Thermophysics and Aeromechanics
Results of studying sinusoidal and varicose instabilities of streaky structures at the nonlinear stage of the laminar-turbulent process in shear flows are presented. The flow behavior in the course of spatial evolution of streaky structures with a secondary high-frequency distuirbance generated on them is discussed. Various scenarios of origination and development of coherent vortex structures examined in physical and numerical experiments are considered. Specific features of the development of sinusoidal and varicose cases of destruction of the steady streamwise streaky structure are demonstrated, such as transverse and streamwise modulation of the structure by the secondary-disturbance frequency, appearance of new streaky structures in the downstream direction, and emergence and evolution of unsteady lambda-type structures localized in space in both cases.
Thermophysics and Aeromechanics, 2004
The investigation results of the controlled experiment of a streaky structure varicose instability in a swept wing boundary layer are presented. The picture of a streaky structure spatial evolution and secondary high-frequency disturbances generated on it is obtained using hot-wire measurements. It is shown that exactly a varicose instability is realized. It has been found that the secondary disturbance increases owing to instability of mean velocity distribution on normal to the wall caused by the streaky structure development. The following features of a varicose breakdown of a longitudinal stationary streaky structure are presented: structure modulation in the longitudinal direction by a secondary disturbance frequency, downstream excitation of new streaky structures, formation and development of nonstationary structures localized in space. In contrast to the boundary layer flow of the unswept wing models, where these structures resemble classical horseshoe structures or lambda-v...
Visualization of sinusoidal and varicose instabilities of streaks in a boundary layer
Journal of Visualization, 2006
Nonlinear instabilities of boundary layer streaks are investigated experimentally. Extensive measurements visualizing the sinusoidal and varicose instabilities of streaky structures at nonlinear stage of the breakdown process in boundary layer are presented. The flow behaviour in the course of spatial evolution of the streaky structures with a secondary high-frequency disturbance generated on them is discussed. Various scenarios of origination and development of coherent vortex structures examined in physical experiments are considered. Specific features of the development of sinusoidal and varicose cases of destruction of the steady streamwise streaks are demonstrated, such as transverse and streamwise modulations of the streak by the secondary-disturbance frequency, appearance of new streaky structures in the downstream direction, and emergence and evolution of unsteady Λ-shaped structures localized in space in both cases.
Temporal development of turbulent boundary layers with embedded streamwise vortices
Theoretical and Computational Fluid Dynamics, 1992
The interaction of streamwise vortices with turbulent boundary layer has been investigated using large-eddy simulation. The initial conditions are a pair of counterrotating Oseen vortices with flow between them directed toward the wall (common-flow-down), superimposed on various instantaneous realizations of a turbulent boundary layer. The time development of the vortices and their interaction with the boundary layer are studied by integrating the filtered Navier-Stokes equations in time. The most important effects of the vortices on the boundary layer are the thinning of the boundary layer between vortices (downwash region) and the thickening of the boundary layer in the upwash region. The vortices first move toward the wall as a result of the self-induced velocity, and then apart from each other because of the image vortices due to the solid wall. The Reynolds stress profiles highlight the highly three-dimensional structure of the turbulent boundary layer modified by the vortices. The presence of significant turbulent activity near the vortex center and in the upwash region suggests that localized instability mechanisms in addition to the convection of turbulent energy by the secondary flow are responsible for this effect. High levels of turbulent kinetic energy and secondary stresses in the vicinity of the vortex center are also observed. The numerical results show good agreement with experimental results.