STRUCTURAL-CHANGES IN TRANSIENT STOKES-FLOW

In his numerical study of oscillatory Stokes flow past particular axis ymmetric bodies, Pozrikidis (6) described the process of separation fr om the body together with the development and decay of eddies in the f luid. Here we extend his results in three different directions. First, the limiting situation is considered when the frequency of oscillatio ns is small, with a description of the singular perturbation features of the resulting flow; the fundamental problem which describes the man ner in which separation occurs is formulated in general, and solved fo r a spheroid. Secondly, some fairly general conditions are presented u nder which separation takes place from the surface of a sphere when th e streaming motion has a variable velocity; these indicate that such a phenomenon should be seen as a common occurrence. Last, the flow due to an oscillatory stokeslet inside a sphere is considered, and it is f ound that the behaviour is effectively quasisteady for the complete cy cle except for a brief period shortly after the reversal in the forcin g term; even for moderate values of the frequency this transition occu pies less than one per cent of the cycle.