Experimental benchmark for optical measurements in complex turbulent flows
The project described here is part of the work carried out by the CEA concerning the design and qualification tests on nuclear reactor components (fuel assemblies, circuit elements, safeguard devices, etc.). It is part of the R&D activities conducted by the CEA in terms of knowledge of the hydro-mechanical and thermo-hydraulic behavior for PWR fuel assemblies, as well as the qualification of assemblies for industrialists. A panel of experimental facilities ranging for moderate size analytical rigs to industrial scale facilities permits to pursue these R&D activities. In such a context, the CEA Cadarache is developing a new CFD grade experiments, called SEQUIN (see figure). This setup is mainly dedicated to the detailed studies of the turbulent flow at the entrance of full fuel nuclear assembly. Such flow exhibits a complex pattern imposed by the different obstacles before entering the rods bundle maintained by grids.
SEQUIN is a “fully transparent” industrial mockup that allows optical measurements of the structure (streamlines, pressure patterns, etc.) and velocities flows. Moreover, due to the materials used, SEQUIN allows refractive index adjustments adapted to optical measurements in complex geometries. The main objective of this post-doctoral work is the preparation of the experiments that will be carried out on SEQUIN. One of the major issues concerns the effect of refractive index adjustment. One hypothesis made here is that it is unlikely that we will be able to get a perfect index matching as in SEQUIN the fluid should be non-expensive (large volume) and non-dangerous both for humans and the experimental facility. To assess the influence of this parameter on SEQUIN experiments, different optical methods will be evaluated considering imperfect index matching, e.g.: PIV (classic and possibly tomographic) [2], Particle Tracking (low and high density) [3] and digital in-line Holography [4]. For this purpose, the post-doctorate will:
• Contribute to the development of an experimental benchmark. In this benchmark, the complexity of the optical pattern will be modified to mimic some elements of SEQUIN using specific and standardized shape for academic purposes.
• Evaluate the performances and the accuracy of the different optical measurement techniques.
• Propose the most suitable optical diagnostic for SEQUIN experiments and perform first optical measurements using SEQUIN (second year).
Experiments will be performed in different places, mainly Cadarache and Marcoule CEA centers and will involve several teams. Therefore, the transportability (compactness, modularity) and reproducibility of the benchmark are important.
+(33) 4 42253251