Computational fluid dynamics (CFD) simulations to predict and visualize the reacting flow dynamics inside a combustor require fine resolution over the spatial and temporal domain, making them computationally very expensive. The traditional time-serial approach for setting up a parallel combustor CFD simulation is to divide the spatial domain between computing nodes and treat the temporal domain sequentially. However, it is well known that spatial domain decomposition techniques are not very efficient especially when the spatial dimension (or mesh count) of the problem is small and a large number of nodes are used, as the communication costs due to data parallelism becomes significant per iteration. Hence, temporal domain decomposition has some attraction for unsteady simulations, particularly on relatively coarse spatial meshes. The purpose of this study is two-fold: (i), to develop a time-parallel CFD simulation method and apply it to solve the transient reactive flow-field in a combustor using an unsteady Reynolds-averaged Navier Stokes (URANS) formulation in the commercial CFD code FLUENT™ and (ii) to investigate its benefits relative to a time-serial approach and its potential use for combustor design optimization. The results show that the time-parallel simulation method correctly captures the unsteady combustor flow evolution but, with the applied time-parallel formulation, a clear speed-up advantage, in terms of wall-clock time, is not obtained relative to the time-serial approach. However, it is clear that the time-parallel simulation method provides multiple stages of transient combustor flow-field solution data whilst converging towards a final converged state. The availability of this resulting data could be used to seed multiple levels of fidelity within the framework of a multi-fidelity co-Kriging based design optimization strategy. Also, only a single simulation would need to be setup from which multiple fidelities are available.
AP-IO: Asynchronous Pipeline I/O for Hiding Periodic Output Cost in CFD Simulation