GPU optimized integration of immersed boundary method and overset mesh framework for moving boundary problems

This paper focuses on a GPU-optimized overset grid framework coupled with a sharp-interface Immersed Boundary Method (IBM) for high-fidelity simulation of incompressible flows involving moving bodies, multi-body interactions, and complex geometries. The method addresses long-standing limitations of overset IBM, such as expensive hole-cutting, donor-search operations, and poor scalability, by leveraging a lightweight sliding-window block reallocation strategy, minimalistic interface maps, and flux-preserving interpolation between coarse and refined meshes. A combined Array-of-Structures / Structure-of-Arrays data structure is devised for efficient management and storage of multiple blocks of the domain. Explicit OpenACC directives leveraging the unified memory architecture enable GPU acceleration. At the same time, a dual-level OpenMP–OpenACC parallelism assigns each overset block to a dedicated GPU, enabling multi-GPU execution without message-passing overhead. The solver is validated and verified across a wide range of canonical and complex cases, including flow past cylinders and spheres, sedimentation of smooth and rough particles, and fluttering plates, with results demonstrating second-order accuracy, local and global mass conservation, and excellent agreement with experimental and numerical benchmarks. High-Reynolds-number propeller simulations confirm DNS-level resolution, with the overset mesh adequately capturing Kolmogorov scales. Multi-body demonstrations involving two flapping robotic butterflies following independent sinusoidal trajectories highlight robust block autonomy and accurate vortex-interaction dynamics. Overall, the proposed framework achieves close to 200× speedup relative to single-core CPU execution, retains accuracy while using significantly fewer grid points than uniform DNS meshes, scales efficiently across multiple GPUs, and establishes a versatile, scalable methodology for simulating turbulent, bio-inspired, and strongly unsteady moving-body flows.