École Nationale Supérieure de
Techniques Avancées

Abstract

This study documents the work conducted on the topological optimization of a diffuser in the frame of an internship in the thermodynamics department of Framatome in Erlangen. With the software STAR-CCM+, Computational Fluid Dynamics (CFD) is applied using Reynolds-Averaged Navier-Stokes (RANS) for the turbulence modeling. First of all, a literature review on diffuser and way to describe their flow is performed. From this review, it appears that geometric parameters such as curvature radius or opening angle have an influence on the flow. A model able to describe the recirculation phenomenon is required. After comparison, the Framatome model is being complemented by the Shear Stress Transport (SST) as suggested by different literature. It showed differences in recirculation modeling which seem worth exploring. The Framatome standard modeling approach for fuel components is a methodology which includes specifics settings for the quadratic k-eps turbulence model. It was thoroughly investigated in the past years for the fuel assembly flow field and pressure drop calculations; besides the turbulence model it includes also specific meshing settings for the trimmed mesh of STAR-CCM+. Independent studies of each influencing parameter such as curvature radius, divergence angle, gap between ligaments reveal general tendency. These parameters will be combined using OpenTurns solver to find the optimal set up in order to minimize a cost function defined by two requirements which are minimizing the pressure losses and homogenizing the flow.