Direct numerical simulations of vortex shedding behind cylinders with spanwise linear nonuniformity

Abstract

Three-dimensional direct numerical simulations of vortex shedding behind cylinders have been performed when the body diameter and the incoming flow involved spanwise linear nonuniformity. Four configurations were considered: the shear flow, the tapered cylinder and their combination which gave rise to namely the adverse and aiding cases. In contrast with the observations of other investigators, these computations highlighted distinct vortical features between the shear case and the tapered case. In addition, it was observed that the shear case and the adverse case (respectively tapered case and aiding case), yielded similarities in flow topology. This phenomenon was explained by the spanwise variations of U/D which seemed to govern these flows. Indeed, it was observed that large spanwise variations of U/D seemed to enhance three dimensionality, through the appearance of vortex adhesions and dislocations. Spanwise cellular pattern of vortex shedding was identified. Their modifications in cell size, junction position and number were correlated with the variation of U/D. In the lee side of the obstacle a wavy secondary motion was identified. Induced secondary flow due to the bending of Karman vortices in the vicinity of vortex adhesion and dislocations was suggested to explain this result.

Shearless and sheared flow past a circular cylinder: Comparative analysis by means of LES

“…Besides the flow configuration considered in the present work, the bluff body aerodynamics is often investigated under conditions of the mean shear being aligned with the body axis. Examples of such investigations are reported in Tavoularis et al (1987), Woo et al (1989) and Parnaudeau et al (2007). In addition to the spanwise shear, the effects of the spanwise non-uniformity in cylinder diameter was also investigated in the latter publication.…”

Cellular vortex shedding behind a tapered circular cylinder

“…The only exception is the numerical study by Parnaudeau et al 14 where they provided some data from the cellular wake pattern behind their tapered circular cylinder. Their objective was limited to study and compare the flow topology of the wake behind a circular cylinder in a linear shear flow with the wake of a tapered circular cylinder in uniform flow.…”

“…These three-dimensionalities can induce significant spanwise variations in the velocity and pressure fields. In contrast, such three-dimensionalities are known to occur if the diameter of the cylinder changes discontinuously [2][3][4] or linearly [5][6][7][8][9][10][11][12][13][14] even at a Reynolds number well below the critical value Ϸ190. Almost all previous studies on the flow past linearly tapered circular cylinders are either in the laminar flow regime [5][6][7][8][9][10][11]15 or in the turbulent flow regime.…”

Frequency characteristics of a vortex flowmeter in various inlet velocity profiles

“…Since the Reynolds number differs in each region, the axis of the shed vortex inclining relative to the vortex generator is expected. 23 Table 2 shows that the shedding frequencies in regions 1-4 (23.3-23.4 Hz) are higher than that in region 5 (20.1 Hz). Figure 8 shows the velocity contours for Case B1 on the central planes for regions 1 and 5 at 0.5 time period.…”