Vorticity transport and wake structure for bluff bodies at finite Reynolds number

This paper is concerned with the structure of recirculating wakes downstream of bluff bodies at finite Reynolds number, and the relationship between these wakes and asymptotic behavior for R→∞. It is shown that recirculating eddies at finite Reynolds number are not necessarily a precursor of the asymptotic phenomenon of separation that is ‘‘predicted’’ via boundary-layer theory. In some cases, such as the flow around deformable gas bubbles, recirculating eddies may appear at intermediate Reynolds numbers, but then disappear with further increase of the Reynolds number. In other cases, recirculating eddies exist downstream of the body at finite Reynolds number that are completely detached from the body. These examples suggest that recirculating eddies at large, but finite Reynolds number do not necessarily imply anything about the solution behavior for R→∞, even for solid bodies where it is usually assumed that wakes for R∼O(10–100) are a manifestation of the same processes that lead to separation of boundary layers for R→∞.