Low-order macroelements for two- and three-dimensional Stokes flow

The use of low-order elements for approximating fluid flow is attractive because all the elemental contributions can be quickly and easily obtained. One of the drawbacks is that low-order elements often give rise to spurious pressure modes or incompatible velocity and pressure approximations. In this paper linear velocity and linear pressure elements are described for both two- and three-dimensional flow that always produce stable solutions provided the elements are assembled into simple macroelements following easily used rules. Some examples of this idea are given for Stokes flow and compared with another popular low-order method.