Abstract
The wake flow patterns associated with flow past a cylinder and a cylinder-pair in tandem configuration are revisited, compared, and evaluated with respect to the streamline patterns generated based on potential flow theory and superposition of various potential flow elements. The wakes, which are vortex shedding in the lee of the cylinder(s), are reproduced by placing pairs of equal but opposite circulation elements in the potential flow field. The strength of the circulation elements determines the size of the vortices produced. The streamline patterns of flow past a pair of unequal cylinders in tandem configuration provide an indirect means to establish the threshold condition for the wake transition from that of a single bluff body to alternating reattachment behavior. This threshold condition is found to be a function of the diameter ratio,d/D(diametersdandD,d≤D), spacing ratio,L/D(centre-to-centre distance,L, to cylinder diameter,D), and equivalent incident flow speed,U.A unique functional relationshipf(L/D,d/D,U) of this threshold condition is established.
Highlights
Flow past a cylinder and two circular cylinders in tandem configuration are common occurrences in many engineering applications, such as mooring lines, riser, and bundled cylinders at offshore installations, bridge piers, and tube bundles in heat exchangers
The streamline patterns suggest that the flow engulfs the two doublets wholly, and the flow patterns are in good agreement with those observed in experiments (Igarashi [2]; Zdravkovich [11])
When d/D is increased to 1.065, the lower streamline shows the tendency of moving upwards but has not yet extended across the axis joining the two cylinder centres. This is similar to the patterns observed between two cylinders with equal diameter at small spacing ratios, whereupon the two cylinders behave as a single bluff body
Summary
Flow past a cylinder and two circular cylinders in tandem configuration are common occurrences in many engineering applications, such as mooring lines, riser, and bundled cylinders at offshore installations, bridge piers, and tube bundles in heat exchangers. Considering the analogous patterns of potential flow streamlines and the flow patterns behind cylinder-pair in tandems, the obvious question arises as to whether one could deduce from these patterns a precise threshold condition analytically and account for the onset of type 2 and type 3 interferences. For this purpose, the authors drew on the potential flow theory approach to generate streamline patterns for the following cases:. (2) flow patterns in the lee of a cylinder-pair, as a function of spacing ratio and diameter ratio, with the aim of determining the threshold spacing ratio for the onset of streamline patterns similar to that of type 2 and type 3 interference
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