title: Lattice Boltzmann method for the fractional advection-diffusion equation.
abstract: 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 superdiffusion, and it 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). The FADE is transformed into an equation similar to an advection-diffusion equation and solved using the lattice Boltzmann 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 they indicate that the method is second-order accurate. The method presented will allow the FADE to be more widely applied to complex mass transport problems in science and engineering.
authors.affiliation: School of Engineering, Liverpool University, Liverpool L69 3GQ, United Kingdom.
authors.forename: J G
authors.initials: JG
authors.lastname: Zhou
authors.affiliation: Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, United Kingdom.
authors.forename: P M
authors.initials: PM
authors.lastname: Haygarth
authors.affiliation: Bangor University, Bangor, Gwynedd LL58 8RF, United Kingdom.
authors.forename: P J A
authors.initials: PJ
authors.lastname: Withers
authors.affiliation: James Hutton Institute, Aberdeen AB15 8QH, United Kingdom.
authors.forename: C J A
authors.initials: CJ
authors.lastname: Macleod
authors.affiliation: Met Office Hadley Centre, Exeter, Devon EX1 3PB, United Kingdom.
authors.forename: P D
authors.initials: PD
authors.lastname: Falloon
authors.affiliation: Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, United Kingdom.
authors.forename: K J
authors.initials: KJ
authors.lastname: Beven
authors.affiliation: Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, United Kingdom.
authors.forename: M C
authors.initials: MC
authors.lastname: Ockenden
authors.affiliation: Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, United Kingdom.
authors.forename: K J
authors.initials: KJ
authors.lastname: Forber
authors.affiliation: Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, United Kingdom.
authors.forename: M J
authors.initials: MJ
authors.lastname: Hollaway
authors.affiliation: Global Sustainability Institute, Anglia Ruskin University, Cambridge CB1 1PT, United Kingdom.
authors.forename: R
authors.initials: R
authors.lastname: Evans
authors.affiliation: Rothamsted Research North Wyke, Okehampton EX20 2SB, Devon, United Kingdom.
authors.forename: A L
authors.initials: AL
authors.lastname: Collins
authors.affiliation: School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom.
authors.forename: K M
authors.initials: KM
authors.lastname: Hiscock
authors.affiliation: Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, United Kingdom.
authors.forename: C
authors.initials: C
authors.lastname: Wearing
authors.affiliation: Met Office Hadley Centre, Exeter, Devon EX1 3PB, United Kingdom.
authors.forename: R
authors.initials: R
authors.lastname: Kahana
authors.affiliation: School of Engineering, Liverpool University, Liverpool L69 3GQ, United Kingdom.
authors.forename: M L
authors.initials: ML
authors.lastname: Villamizar Velez