Unsteady flows in elastico-viscous liquids
During recent years the unsteady flow of elastico-viscous liquids in various geometries has attracted much attention. Ting (1963) considered a number of unsteady flow problems for the “second order” fluid of Coleman and Noll (1960) but found that bounded solutions could not be obtained for the cases of physical interest. Waters and King (1970, 1971) found that bounded solutions could be obtained to these problems for liquids with equations of state of the type proposed by Oldroyd(1950). The problems considered by these authors all involved the generation or decay of steady flow in fairly simple geometries. Waters and King found that the flows were strongly affected by the presence of elasticity and that, for quite realistic values of the elastic parameters, the velocity profiles oscillated about their final steady form before tending to it. Of course it has been known for some time that the presence of elasticity has a considerable effect in unsteady flow situations. Often experimentalists try to eliminate such effects from their experiments. Sometimes unsteady behaviour is actually used to determine rheological parameters, for example, in oscillatory experiments and Balance Rheometers (Walters, 1970).
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