  We utilize the Open Accelerator (OpenACC) approach for graphics processing
unit (GPU) accelerated particle-resolved thermal lattice Boltzmann (LB)
simulation. We adopt the momentum-exchange method to calculate fluid-particle
interactions to preserve the simplicity of the LB method. To address load
imbalance issues, we extend the indirect addressing method to collect
fluid-particle link information at each timestep and store indices of
fluid-particle link in a fixed index array. We simulate the sedimentation of
4,800 hot particles in cold fluids with a domain size of $4000^{2}$, and the
simulation achieves 1750 million lattice updates per second (MLUPS) on a single
GPU. Furthermore, we implement a hybrid OpenACC and message passing interface
(MPI) approach for multi-GPU accelerated simulation. This approach incorporates
four optimization strategies, including building domain lists, utilizing
request-answer communication, overlapping communications with computations, and
executing computation tasks concurrently. By reducing data communication
between GPUs, hiding communication latency through overlapping computation, and
increasing the utilization of GPU resources, we achieve improved performance,
reaching 10846 MLUPS using 8 GPUs. Our results demonstrate that the
OpenACC-based GPU acceleration is promising for particle-resolved thermal
lattice Boltzmann simulation.
