An OpenFOAM solver for radon migration in indoor spaces

Accurate numerical simulation of radon migration dynamics in indoor environments is critical for mitigating radon-induced health risks and enhancing air quality management strategies. However, there is a lack of dedicated solvers for this purpose. This paper presents the development of a novel OpenFOAM-based solver, RnFOAM, which uniquely integrates turbulent diffusion into radon migration modeling. The solver has two main components: radon migration model represented by a governing equation with transient, diffusion, advection, decay, and source terms; and k-ε turbulence model for simulating indoor airflow as the initial condition for advection velocity in the advection term of the radon migration model. We used the finite volume method (FVM) to numerically solve these equations. To validate the solver, an experimental setup was used to simulate radon emanating from concrete walls into indoor spaces. The results showed high prediction accuracy, with a maximum difference of no more than 15 % between simulated and measured values, and a minimum difference of just 0.9 %. The comparison results between the RnFOAM solver and the commercial software COMSOL Multiphysics show that the relative difference between the simulation results of the two for the same model is only 0.8 %, and the convergence speed of the RnFOAM solver is much higher than that of COMSOL Multiphysics. Finally, we simulated radon migration in an underground space and analyzed different ventilation strategies to identify effective methods for reducing radon concentration.