  High fidelity Computational Fluid Dynamics simulations are generally
associated with large computing requirements, which are progressively acute
with each new generation of supercomputers. However, significant research
efforts are required to unlock the computing power of leading-edge systems,
currently referred to as pre-Exascale systems, based on increasingly complex
architectures. In this paper, we present the approach implemented in the
computational mechanics code Alya. We describe in detail the parallelization
strategy implemented to fully exploit the different levels of parallelism,
together with a novel co-execution method for the efficient utilization of
heterogeneous CPU/GPU architectures. The latter is based on a multi-code
co-execution approach with a dynamic load balancing mechanism. The assessment
of the performance of all the proposed strategies has been carried out for
airplane simulations on the POWER9 architecture accelerated with NVIDIA Volta
V100 GPUs.
