Non-Newtonian viscous oscillating free surface jets, and a new strain-rate dependent viscosity form for flows experiencing low strain rates |
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Authors: | Stephen E. Bechtel Nivine T. Youssef M. Gregory Forest Hong Zhou Kurt W. Koelling |
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Affiliation: | (1) Department of Mechanical Engineering The Ohio State University Columbus, OH 43210, USA e-mail: bechtel@seb2.eng.ohio-state.edu, US;(2) Department of Mathematics University of North Carolina Chapel Hill Chapel Hill, North Carolina 27599-3250 USA, US;(3) Department of Chemical Engineering The Ohio State University Columbus, OH 43210, USA, US |
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Abstract: | A model for oscillating free surface jet flow of a fluid from an elliptical orifice, together with experimental measurements, can be exploited to characterize the elongational viscosity of non-Newtonian inelastic fluids. The oscillating jet flow is predominantly elongational, with a small strain that oscillates rapidly between large and zero strain rates. We find that to reproduce the experimentally observed steady oscillating jet flow in model simulations, the assumed form of the non-Newtonian viscosity as a function of strain rate must have zero gradient, i.e., be Newtonian, at zero strain rate (a behavior exhibited, in general, by real inelastic fluids). We demonstrate that the Cross, Carreau, Prandtl-Eyring, and Powell-Eyring forms, although they have finite viscosity at zero strain rate, have either nonzero or even unbounded gradient at zero, and hence are unable to model oscillating jet behavior. We propose a new non-Newtonian viscous form which has all of the desirable features of existing forms (high and low strain rate plateaus, with adjustable location and steepness of the transition) and the additional feature of Newtonian behavior at low strain rates. Received: 7 February 2000 Accepted: 31 October 2000 |
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Keywords: | Oscillating free surface jet Strain-rate thinning viscosity Generalized Newtonian fluid Non-Newtonian inelastic fluid Rheometry Extensional flows |
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