A stable and accurate convective modelling procedure based on quadratic upstream interpolation

A convective modelling procedure is presented which avoids the stability problems of central differencing while remaining free of the inaccuracies of numerical diffusion associated with upstream differencing. For combined convection and diffusion the number of operations at each grid point is comparable to that of standard upstream-pluscentral differencing — however, highly accurate solutions can be obtained with a grid spacing much larger than that required by conventional methods for comparable accuracy, with obvious practical advantaged in terms of both speed and storage. The algorithm is based on a conservative control-volume formulation with cell wall values of each field variable written in terms of a quadratic interpolation using in any one coordinate direction the two adjacent nodal values together with the value at the next upstream node. This results in a convective differencing scheme with greater formal accuracy than central differencing while retaining the basic stable convective sensitivity property of upstream-weighted schemes. The consistent treatment of diffusion terms is equivalent to central differencing. With careful modelling, numerical boundary conditions are not troublesome. Some idealized problems are studied, showing the practical advantages of the method over other schemes in comparison with exact solutions. An application to a complex unsteady two-dimensional flow is briefly discussed.