Unsteady separation past moving surfaces

Abstract

Unsteady boundary-layer development over moving walls in the limit of infinite Reynolds number is investigated using both the Eulerian and Lagrangian formulations. To illustrate general trends, two model problems are considered, namely the translating and rotating circular cylinder and a vortex convected in a uniform flow above an infinite flat plate. To enhance computational speed and accuracy for the Lagrangian formulation, a remeshing algorithm is developed. The calculated results show that unsteady separation is delayed with increasing wall speed and is eventually suppressed when the speed of the separation singularity approaches that of the local mainstream velocity. This suppression is also described analytically. Only 'upstreamslipping' separation is found to occur in the model problems. The changes in the topological features of the flow just prior to the separation that occur with increasing wall speed are discussed.

Fluid flow due to a cylinder rolling along ground

“…It would nevertheless be of some interest to examine the classical attached form with assumed potential flow almost everywhere. The steady case then would seem to have limited relevance but the unsteady case may exhibit lift-off of the viscous effects similar to that in the Degani et al (1998) study. Again, although high shear stresses are induced near the contact point, as shown in Section 2 and the results of Section 3, the local behaviour there is actually of lubrication type and so is free of inertia.…”

“…The additional effects of a free stream have also been addressed (Koromilas and Telionis, 1980;Nikolayev, 1982;Ece et al, 1984;Sychev, 1987;Lam, 1988;Chipman and Duck, 1993;Degani et al, 1998). The influence of contact with moving ground, on the other hand, which is central to the present investigation, appears not to have been seriously examined as far as we know.…”

Unsteady separation in vortex-induced boundary layers

“…Not only do the asymptotics provide knowledge of the dominant physics during the evolution of unsteady separation, the mathematical formulations of the asymptotic stages themselves provide reduced-physics models that can be used in control algorithms. Although this line of research into control of unsteady separation has been pursued experimentally, very little work has been done analytically and/or numerically (see [60,61] and the references therein).…”

Vortex shedding in shear flow past tandem square cylinders in the vicinity of a plane wall

“…The wall pressure recovers near the gap entrance of the downstream cylinder and again encounters an adverse pressure gradient below the cylinder to encounter a separation from the wall. The interaction of a shear layer with a finite core vortex leading to unsteady separation has been studied by Degani et al (1998) and Sengupta et al (2003). The wall encounters separation further downstream and this separation is periodic with the vortex shedding from the downstream cylinder.…”