CG-LBM-CUDA: An open-source C/CUDA C implementation and verification package for color-gradient MRT lattice Boltzmann simulation of immiscible two-phase flow

CG-LBM-CUDA is an open-source C/CUDA C software package that implements established color-gradient multiple-relaxation-time lattice Boltzmann formulations for immiscible two-phase flow. The package is designed as a computational-science implementation and verification package rather than a new multiphase LBM formulation. It provides a serial C baseline solver, a CUDA C solver, validation scripts, example cases, and reference result files. The CUDA C implementation follows a node-wise data-parallel mapping with stage-wise kernel decomposition, CUDA constant-memory usage for read-only coefficients, ping-pong PDF buffers for streaming, and reduced host–device data transfers. The software reproduces the flat-surface sessile-droplet contact-angle benchmark of Xu, Liu, and Valocchi for prescribed contact angles of 60°, 90°, and 120°. It also includes CPU–GPU final-field comparisons, PDF-based mass-conservation diagnostics, velocity diagnostics, and stage-wise numerical equivalence checks. The central verification feature is the stage-wise comparison workflow, which records intermediate fields after individual LBM operations and helps distinguish local implementation discrepancies from long-time floating-point drift. The package is intended to support users implementing, validating, and porting color-gradient MRT-LBM solvers to CUDA C-based GPU architectures.