Extension of an exponential discretization scheme to multidimensional convection–diffusion problems

ENATE (Enhanced Numerical Approximation of a Transport Equation) is a high-order exponential scheme for convection–diffusion problems, such as those that govern the transport of fluid properties in a flow field. The scheme was intended to be employed in fluid-related transport equations, although it can be used for any inhomogeneous second-order ordinary differential equation. The value of a variable at a generic point is related to those of adjacent nodes via an algebraic equation. Thus, a three-point stencil is associated to each node. The coefficients of this equation contain integrals of some fluid and flow parameters. One important property is that the scheme allows to obtain a machine-accurate solution of an inhomogeneous transport equation if these integrals can be obtained analytically. As the scheme is essentially one-dimensional, getting the machine-accurate solution of multidimensional problems is not guaranteed even in cases where ENATE integrals are analytic along each coordinate. In this regard the paper presents a simple way of getting solutions in multidimensional problems while still using the one-dimensional formulation. Moreover, if the problem is such that the solution is machine-accurate in the one-dimensional problem along coordinate lines, it will also be for the multidimensional domain. Two different methods of evaluating those terms that come out of the discretization will be explained and compared in various cases