Flux‐Corrected Transport with MT3DMS for Positive Solution of Transport with Full‐Tensor Dispersion. Issue 3 (13th January 2020)

• Record Type: Journal Article
• Authors: Yan, Shuo; Valocchi, Albert J.
• Is Part Of: Ground water. Volume 58:Issue 3(2020)
• Page Start: 338
• Page End: 348
• Publication Date: 2020-01-13
• Subjects: Groundwater -- Periodicals; Wells -- Periodicals; Eau souterraine -- Périodiques; Puits -- Périodiques; Grondwater; Eau souterraine; Puits; Electronic journals; Périodique électronique (Descripteur de forme); Ressource Internet (Descripteur de forme); 551.49
• DOI: 10.1111/gwat.12976
• Languages: English
• ISSNs: 0017-467X

Abstract

Abstract: Solute transport is usually modeled by the advection‐dispersion‐reaction equation. In the standard approach, mechanical dispersion is a tensor with principal directions parallel and perpendicular to the flow vector. Since realistic scenarios include nonuniform and unsteady flow fields, the governing equation has full tensor mechanical dispersion. When conventional grid‐based numerical methods are used, approximation of the cross terms arising from the off‐diagonal terms cause nonphysical solution with oscillations. As an example, for the common scenario of contaminant input into a domain with zero initial concentration, the cross‐dispersion terms can result in negative concentrations that can wreak havoc in reactive transport applications. To address this issue, we use the well‐known flux‐corrected‐transport (FCT) technique for a standard finite volume method. Although FCT has most often been used to eliminate oscillations resulting from discretization of the advection term for explicit time stepping, we show that it can be adapted for full‐tensor dispersion and implicit time stepping. Unlike other approaches based on new discretization techniques (e.g., mimetic finite difference, nonlinear finite volume), FCT has the advantage of being flexible and widely applicable. Implementation of FCT requires solving an additional system of equations at each time step, using a modified "low order" matrix and a modified right‐hand‐side vector. To demonstrate the flexibility of FCT, we have modified the well‐known and widely used groundwater solute transport simulator, MT3DMS. We apply the new simulator, MT3DMS‐FCT, to several benchmark problems that suffer from negative concentrations when using MT3DMS. The new results are mass conservative and strictly nonnegative.