Experimental characterization of the 3D dynamics of a laminar shallow vortex dipole

Abstract

OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. Abstract Experimental results on the dynamics of a vortex dipole evolving in a shallow fluid layer are presented. In particular, the generation of a spanwise vortex at the front of the dipole is observed in agreement with previous experiments at larger Reynolds numbers. The results show that this secondary vortex is of comparable strength to the dipole. The present physical analysis suggests that the origin of this structure involves the stretching induced by the dipole of the boundary-layer vorticity generated by the dipole's advection over the no-slip bottom.

Dynamics and structure of decaying shallow dipolar vortices

“…Besides observing a spanwise vortex in front of the vortex dipole, they also measured large non-negligible vertical velocities-which impair the two-dimensionality of the flow-in the vortex cores of the dipole. A spanwise vortex was also observed by Lacaze et al, 8 who performed laboratory experiments on shallow laminar dipolar vortices generated by two closing flaps. As a continuation of those experiments, Lacaze and co-workers have set out to investigate thoroughly the dynamics of the spanwise vortex ͑personal communication͒.…”

“…The generation mechanism used in the experiments does not seem to have a large effect on the overall characteristics of the flow evolution. For example, Lacaze et al 8 performed one experiment where the dipole was generated using two closing flaps with ␦ = 0.3 and ␦ 2 Re= 20 ͑this is the same value of ␦ 2 Re used in the simulations presented for the 3D flow regime͒. In this experiment, the vorticity extrema were found in bands at the front of the dipole and close to its symmetry axis, and a strong spanwise vortex developed like also observed in our experiments and numerical simulations.…”

“…3,[6][7][8] To quantify the strength of these secondary motions, we consider the following quantities: ͑1͒ the normalized horizontal divergence at the surface ͑z =1͒, ⌬͑t͒ = ͐ A H ͉١ · v͑x,y,1,t͉͒dxdy…”

Dynamics of isolated vortices in shallow flows

“…6 shows a sketch of the experimental setup used in the shallow water table at IfH filled with water depth of H ¼ 2 cm for all the experiments reported by Seol and Jirka (2009). The dipole is generated by the rotation of two vertical flaps (Billant and Chomaz, 2000;Lacaze et al, 2009). Two vertical plates are attached to stepper motors that drive the rotation speed and rotating angle controlled by a PC.…”

Experimental and Theoretical Advances in Fluid Dynamics

“…More recently Lacaze et al (2010) present experimental results on the dynamics of a vortex dipole evolving in a shallow fluid layer and show the existence of three dimensional effects. A span wise vortex is formed in front of dipole and then vertical motion is generated.…”