An ef®cient boundary element solution of the motion of inelastic non-Newtonian¯uids at low Reynolds number is presented in this paper. For the numerical solution all the domain integrals of the boundary element formulation have been transformed into equivalent boundary integrals by means of the dual reciprocity method (DRM). To achieve an accurate approximation of the non-linear and non-Newtonian terms two major improvements have been made to the DRM, namely the use of augmented thin plate splines as interpolation functions, and the partition of the entire domain into smaller subregions or domain decomposition. In each subregion or domain element the DRM was applied together with some additional equations that ensure continuity on the interfaces between adjacent subdomains. After applying the boundary conditions the ®nal systems of equations will be sparse and the approximation of the nonlinear terms will be more localised than in the traditional DRM. This new method known as multidomain dual reciprocity (MD-DRM) has been used to solve several non-Newtonian problems including the pressure driven¯ow of a power law¯uid, the Couette¯ow and two simulations of industrial polymer mixers.
IntroductionThe term non-Newtonian denotes a¯uid whose constitutive equation is not the ordinary Newtonian form that leads to the Navier±Stokes equations. The behaviour of the non-Newtonian¯uids is strongly dependent upon the viscosity variations within the domain. Most non-Newtonian¯uids such as polymers have a viscosity which is a decreasing function of the shear rate, this characteristic is known as shear thinning [1]. Among all shear-thinning¯u ids, polymers are one of the most importants due to their rapid expansion and numerous industrial applications. The viscosity of an inelastic non-Newtonian¯uid can be calculated through several mathematical models such as the power law model; the Carreau model and the hyperbolic tangent model (see [1,2]). All these models are inelastic for they do not include any of the hysteresis or memory effects described by Bird et al. [3], Larson [4], and Tanner [5]. Since the viscosity of inelastic non-Newtonian¯uids is shear rate dependent, it follows that the mathematical models governing the¯ow motion of such uids are nonlinear even in the case when inertia effects can be neglected, i.e. at low Reynolds number. This type of ow process requires sophisticated numerical solution techniques.The application of the boundary element method (BEM) to a non-Newtonian problem requires ®nding a fundamental solution of the system of governing equations including all the nonlinear terms from the stress tensor. However, since such fundamental solution for a general model is not possible to be known, it is necessary to lump the nonlinear terms into a pseudo-body force leading to domain integrals that can be evaluated by using the cell integration approach (Cell-BEM) [6]. Although this method is effective and general, it makes the BEM lose its boundary only nature resulting in a numerical scheme several orders of ma...