Lattice Boltzmann method for fractional advection-diffusion equation

Mass transport such as movement of phosphorus in soils and solutes in rivers is a natural phenomenon and its study plays an important role in science and engineering. It is found that there are numerous practical diffusion phenomena that do not obey the classical advection-diffusion equation (ADE). Such diffusion is called abnormal or super diffusion and is well described using a fractional advection-diffusion equation (FADE). The FADE finds a wide range of applications in various areas with great potential for studying complex mass transport in real hydrological systems. However, solution to the FADE is difficult and the existing numerical methods are complicated and inefficient. In this study, a fresh lattice Boltzmann method is developed for solving the fractional advection-diffusion equation (LabFADE). For the first time the FADE is transformed into an equation similar to an advection-diffusion equation and solved using the lattice Botlzmann method. The LabFADE has all the advantages of the conventional lattice Boltzmann method and avoids a complex solution procedure, unlike other existing numerical methods. The method has been validated through simulations of several benchmark tests: a point source diffusion, a boundary value problem of steady diffusion, and an initial-boundary value problem of unsteady diffusion with the coexistence of source and sink terms. In addition, by including the effects of the skewness β, the fractional order α and the single relaxation time τ , the accuracy and convergence of the method have been assessed. The numerical predictions are compared with the analytical solutions and indicate that the method is 2nd order accurate. The new method will allow the FADE to be more widely applied to complex mass transport problems in science and engineering. PACS numbers: 47.11.-j, 92.40.-t, 91.62.Rt ∗Electronic address: [email protected] 2