FluTAS: a GPU-accelarated solver for multiphase flow applications

A numerical tool for GPU-accelerated simulations of fluid transport and multiphase flows is presented. Starting from the single-phase in-house solver CaNS-GPU (Costa et. al, Comput. Math. with Appl. 2021), the algebraic volume of fluid method MTHINC (Satoshi Ii et al., J. Comput. Phys. 2012) has been ported to GPU using OpenACC directives. Specific care has been paid to the parallelization of the Poisson solver where, optionally, to further reduce the communications among devices, an elliptic solver, based on a slab decomposition, has been included showing remarkable advantages in terms of the overall scalability. Next, to further expand the capabilities of the code, thermal effects have been ported in the accelerated version either in the Boussinesq approximation or in the more general low Mach framework. The entire code has been thoroughly tested first with canonical benchmarks of multiphase flows (e.g., Zalesak disk and three-dimensional rising bubble) and then employed in two more demanding configurations: bubbles in homogeneous isotropic turbulence and two-layer Rayleigh-Bernard convection. Both cases show remarkable potentials for simulations of multiphase flows on accelerated architectures.