Prace Call: 17th
ID: 2018184409, Leader: Riccardo Broglia
Affiliation: CNR-INSEAN, IT
Research Field: Engineering
Collaborators: Antonio Posa CNR-INSEAN IT
Resource Awarded: 31.5 Mil. core hours on Marconi - KNL
Interaction of vortices with obstacles or bodies, as rudders or wings, is a common scenario in several practical flow problems, especially in naval and aeronautical fields. However, accurate numerical studies on this topic are very limited. This is mainly due to the demanding simulation of coherent structures, as well as boundary layers, at Reynolds numbers typical of engineering problems, requiring huge computational resources and highly accurate numerical tools with optimal conservation properties. For instance, conventional - albeit still challenging - numerical techniques, as those resolving the Reynolds-averaged Navier-Stokes (RANS) equations, demonstrated to be unsuitable to simulate properly coherent structures and to handle separation phenomena, as those tied to boundary layer/vortex interaction, due to their time-averaged approach and important modelling assumption on turbulence. Detached-eddy simulation (DES) is obviously a better alternative, since vortices are directly resolved, with no turbulence modelling, but boundary layers are tackled via a RANS methodology, with some significant drawbacks on the accuracy of the overall approach. Here our target is to simulate via Large Eddy Simulation (LES) the behavior of tip and hub vortices shed by a marine propeller in presence of a downstream rudder (hydrofoil) for three different load conditions (rotational speeds). This will allow us to assess how tip and hub vortices, featuring variable intensity across load conditions, interact with the downstream obstacle and its boundary layer and the way such interaction affects their stability and footprint on turbulence statistics. In a similar way the effect on the boundary layer over the rudder can be analyzed. Although we are going to consider a naval hydrodynamic problem, we expect that the impact of this study will go beyond the particular application, based on the small number of high-fidelity computations in this class of flow problems. Resolution requirements of LES, in both space and time, are very demanding in the present class of flows, since all important energy-carrying structures need to be resolved. Such requirements can be met only on large supercomputers and leadership computing facilities. The solver we are going to adopt in this study, coupling LES and the Immersed-Boundary (IB) method, has been already validated on several practical flow problems, involving also rotating machinery applications, turbines and propellers, demonstrating accuracy, performance and stability. It was tested on many parallel clusters in the framework of several HPC grants, including also Marconi-KNL at CINECA, which is the machine where we are planning to run the simulations of interest of the present proposal. Therefore, both computational tool and setup of the simulations are ready for production runs.