SPECTRAL ELEMENTS FOR VISCOELASTIC FLOWS WITH CHANGE OF TYPE

The spectral element method is used on periodic flows containing chang e of type of the vorticity equation. On slightly perturbed viscometric flows in a channel, the method is compared to the so-called EVSS fini te element method and to analytical results when they are available. I t is found that the method performs very well on all flows examined an d that the computational cost is reduced compared to EVSS. The analysi s of the uniform perturbed flow of a Maxwell fluid has revealed an unu sual condition on the polynomial space containing the extra-stress rep resentations. The technique is also applied to study the increase of t he flow resistance in a periodically constricted tube. Results are com pared with existing ones produced by means of the mixed pseudospectral -finite difference method (PCFD). Excellent agreement is found when co mparing flow resistance. Explanation of the observed numerical difficu lties is also investigated by inspection of the vorticity patterns cor responding to several pairs of Weissenberg and Reynolds numbers.