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E L S E V I E R J, Non-Newtonian Fluid Mech., 57 (1995)ix-xi

Editorial

This issue contains a small sample of the papers presented at an International Symposium on Viscoelastic Fluids which was held in Tobago in January 1994. The Symposium was organized under the auspices of the Caribbean Congress of Fluid Dynamics, with the support of the British and Mexican Societies of Rheology, The International Union of Theoretical and Applied Mechanics gave a grant to assist the venture and the co-chairmen, Dr. H. Ramkissoon and Dr. C.J.S. Petrie, had the support of their universities, the University of the West Indies (the St Augustine campus in Trinidad) and the University of Newcastle upon Tyne (UK).

The aims of the symposium were both to provide a forum for the exchange of scientific ideas at an international level and to bring international experts and the local Caribbean rheological community together. That this latter aim is taken seriously by our hosts may be inferred from the presence at the opening ceremony

A view from the Conference Hotel.

0377-0257/95/$09.50 © 1995 - Elsevier Science S.A. All rights reserved SSDI 0377- 0257(94)01291 - 1

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of Mr L Denoon, Head of the Tobago House of Assembly, and Professor R Saunders, President of the Caribbean Academy of Sciences. More detailed accounts of the symposium may be found elsewhere [1,2].

The sample of papers published here is representative both in the sense that the authors come from three continents and that the topics cover theoretical, computa- tional and experimental approaches to viscoelastic fluid flow. In addition the sample is representative of the aims of the symposium, since it contains one of the five contributions with Caribbean authorship and a contribution derived from one of the invited plenary lectures, namely the paper by Degand and Walters, which presents in detail one topic which was addressed in the plenary lecture by Professor Walters. A number of the other contributed papers have already been published.

The four plenary lectures were given by K. Walters, N. Phan-Thien, A.S. Lodge and L.G. Leal, who surveyed, respectively, non-Newtonian fluid mechanics (over thirty years), the mechanics of suspensions and particulate solids (with emphasis on computational aspects), polymer elasticity (in experiment and theory) and flows with significant extensional contributions. There were varying degrees of optimism among these four speakers on the prospects of accurate theoretical prediction of viscoelastic flow phenomena. The fact that these differing views have not got as far as the printed page perhaps reflects the lack of a firm basis for the conflicting prognostications. The underlying question, of which constitutive equation should be used, either by experimenters to represent their data concisely (by fitting a few parameters) or by theorists to model complex flows, is clearly not ready for a comprehensive resolution. It may, indeed, legitimately be asked whether determin- ing a "correct" constitutive equation is feasible for any class of non-Newtonian fluids, or even for a single rheologically complex fluid in all flow situations. This is not, of course, a message of despair, since it promises useful employment for rheologists for the foreseeable future. More seriously, the message is that, at least in the present state of the art, different constitutive equations may be appropriate for different flow situations, even with a single material.

The meeting was small, with 38 participants, and 26 presentations over four days, and this made for an informal atmosphere and lively discussion. A flavour of the symposium can be obtained from a list of the sixteen contributed papers which are not published here:

Y.Y. Renardy, "Spurt and instability in a two-layer Johnson-Segalman liquid", K.E.P. Adewale and A.I. Leonov, "The modelling of spurt flows of molten polymers", P. Espanol, "Earthquake fault model for stick-slip dynamics in melt fracture", P.N. Kaloni, "On the flow of a viscoelastic fluid through a curved pipe", M. Renardy, "The stresses of an upper convected Maxwell fluid in a Newto- nian velocity field near a reentrant corner", R. Keunings, R. Aggarwal, P. Henriksen, D. Vanderstraeten and O. Zone, "Developments in the parallel computation of viscoelastic flows", E. Mitsoulis and G. Barakos, "Viscoelastic effects in blade coating",

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J. Honerkamp and J. Weese, "Modern methods of data processing in rheol- ogy", D.D. Joseph, "Extrapolation of normal stress measurements", J. Mewis, J. Vermant and P. Moldenaers, "Transient behaviour of thermo- tropic liquid crystalline polymers", L.F. del Castillo, F.C. P6rez-Cardenas, J.E. Puig A and R.M. Jimenez- Amezcua, "The Kohlrausch stress relaxation function for polydispersed linear polymeric fluids", C. Friedrich, "The fractional calculus approach to rheological constitutive equations", P.A.P. Hastilow, D.A. Janes and R.C.E. Guy, "A comparison of rheological models for extrusion-cooked wheat starch with data from both slit-die and parallel plate rotational oscillation rheometry", T. Peters and R. Whiting, "Viscoelasticity in asphalts", B. Mena, J. Hernandez, C.A. Morales, B. Motta and A.von Ziegler, "A new kind of shear-elongational rheometer", D.D. Joseph also presented two videos: "Water lubricated pipeline flow of oil" and "Particle motion in Newtonian and Non-Newtonian fluids".

This list, in the order of presentation at the symposium, gives an idea of the variety of topic which is judged worthy of study by the scientific community involved in rheology and non-Newtonian fluid mechanics. It is presented here because it seems to me, from involvement in the symposium organization and editorially, that the selection is wider than that normally encountered in the pages of this journal - - and that is intended as criticism neither of symposium nor of journal. There is still a tradition in rheology, which many of us value, of discussing scientific work across a wide range of topics. This provides a counterbalance to the necessary specializa- tion for which workshops such as those on extensional flow [3] or numerical simulation [4] cater very successfully.

Chris Petrie, Newcastle upon Tyne,

September 1994

References

[1] C. Friedrich, On the trail of Robinson Crusoe, Rheology, 4 (1994) 1, 34 37. [2] C.J.S. Petrie, International symposium on viscoelastic fluids, Bulletin of the British Society of

Rheology, 37 (1994) 26-31. [3] Special Issue: Proceedings of an International Conference on Extensional Flow, held at Combloux,

France, 20th-23rd March 1989, J. Non-Newtonian Fluid Mech., 35 (1990) 85-470. [4] R.A. Brown and G.H. McKinley, Report on the VIIIth International Workshop on Numerical

Methods in Viscoelastic Flows, J. Non-Newtonian Fluid Mech., 52 (1994) 407-413.