Abstract
Reasonable agreement between an Oldroyd-type theory and experiment for helical flows of viscoelastic fluids was found. However, it was not found possible to predict accurately the experimental drag on a sphere using “constants” found from helical flow tests. It is concluded that the flow curve of the Oldroyd fluid is unrealistic and must be modified for practical use. A scheme is suggested which would allow the interpretation of any set of data given the flow curves, normal stresses and relaxation spectrum from experiments. It is suggested that few engineering calculations will need the simultaneous consideration of all the factors mentioned above and separate cases are considered. For the case of unsteady flows where normal stress effects are unimportant, the modified Oldroyd equation will be simple and useful; for more complex cases it may not be the simplest approach. Some remarks on the practical use and meaning of falling-ball tests in non-Newtonian fluids are also given.
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