Vortex interaction in the formation region of a grooved circular cylinder

Based on the conditional sampling technique, the present study in the formation region of the flow over a partially grooved circular cylinder of smooth half and groove half of theta(g) = +90 degrees over a Reynolds number range of 7.7 x 10(3) - 1.3 x 10(5) establishes the presence of the Gerrard-Bloor secondary vortices in the subcritical, critical, supercritical and transcritical regimes of a smooth cylinder. Quantitatively, there is evidence of mutual interaction of the primary vortex sheet and the secondary vortices. Due to the presence of the secondary vortices, the development of the primary vortex sheet is affected, depending on the energy of the small-scale vortices. The effect of the primary vortex sheet is to enhance the development of the secondary vortices under its strain field. The degree of mutual interaction depends on the energy of the secondary vortices. The present findings on the small-scale streamwise wake vortices on the groove half also indicate similar phenomena. (C) 1999 The Japan Society of Fluid Mechanics and Elsevier Science B.V. All rights reserved.