Large and heterogeneous data handling for helicopter CFD

Context The CFD projects at ONERA are involving several codes on super-computers, they use and produce very large amount of data. In the workflow of these CFD simulations, the data are heterogeneous, time-dependent and most of the time generated during a parallel computation. The usual file based storage can be achieved by means of a local and precise procedure giving rules for directories, file names, contents of files... but the features provided by CGNS [1] offer a more formal, documented, interoperable and actually operational way of handling these data. We illustrate such a use through the EU GOAHEAD project in which the applied aerodynamics department of ONERA had to compute a complete helicopter configuration with a set of chimera grids provided by an external partner using a different CFD solver [2]. Standardized complex data The GOAHEAD application includes a high speed CFD simulation of a complete NH90-like helicopter model in the DNW-LLF wind tunnel, including main and tail rotors, strut, fuselage, hub and wind tunnel walls. The computational tools have to be interoperable and eventually re-used for other cases. Thus, the open standard for data management is a strong requirement. Also the very large amount of unsteady data could not be handled without the help of a data model: we have to handle traceability between grids, computation parameters, restart data, results... The grids were defined and provided by DLR and were not to be modified by the application. Some data changes had nevertheless to be introduced in these grids. For example, the different grids have to be moved in their expected location for each computation run, the assembly of files in a global CGNS tree led to name collision. All modifications are performed as decorations, this means the actual data is unchanged. The decoration preprocessing needs not to be aware of the configuration, number of zones, zone names, boundary conditions and all other information. Thanks to the public standard it discovers the required information during the files parse. The chimera technique being used to compute the motion of the different blades with respect to the fuselage and the wind-tunnel, the masking, blanking, neighbourhood search is also performed by preprocessing tools using pyCGNS [3]. The tools are looking for zones, their