Experimental and Numerical Analysis for Fluid-Structure Interaction for an Enclosed Hexagonal Assembly

Abstract

This paper is related to fluid-structure interaction analysis of sodium cooled fast reactors core (Na-FBR). Sudden liquid evacuation between assemblies could lead to overall core movements (flowering and compaction) causing variations of core reactivity. The comprehension of the structure behavior during the evacuation could improve the knowledge about some SCRAMs for negative reactivity occurred in PHÉNIX reactor and could contribute on the study of the dynamic behavior of a FBR core. An experimental facility (PISE-2c) is designed composed by a Poly-methyl methacrylate hexagonal rods (2D-plan similitude with PHÉNIX assembly) with a very thin gap between assemblies. Another experimental device (PISE-1a) is designed and composed by a single hexagonal rod for testing the dynamic characteristics. Different experiments are envisaged: free vibrations and oscillations during water injection. A phenomenological analysis is reported showing the flow behavior in the gap and the structure response. Also computational simulations are presented in this paper. An efficient numerical method is used to solve Navier-Stokes equations coupled with structure dynamic equation. The numerical method is verified by the comparison of analytic models and experiments.

Added Mass and Damping of an Hexagonal Rod Vibrating in Highly Confined Viscous Fluids

“…2 Analytical solution for a cylinder vibrating in a small viscous gap and extension to hexagonal prisms An original analytical solution is obtained for the forced vibration of a cylinder in a very confined viscous fluid with initially stagnant fluid. It was presented in a previous communication [13]. We resume here the main features and we give in appendix the (previously unpublished) explicit expression.…”

“…The analytical study was used to design a test rig accounting for a single Poly-methyl methacrylate (PMMA) hexagonal prism enclosed in a 7 mm gap filled with water and named PISE-1a [13]. The prism is 71,4 mm of side and 500 mm tall.A picture is provided in Fig.…”

“…In a previous communication [13], we presented an original analytical solution for the vibration of a two-dimensional cylindrical rod immersed in a fluid confined within a shell. We validated against it a coupled fluid-structure numerical solver that we used to investigate the flow differences between hexagonal and circular annulus.…”

“…3 Extension of the cylindrical analytical solution to the hexagonal prism Sargentini et al [13] set up a 2D numerical tool which solves the full Navier-Stokes equation coupled to structure dynamics by means of Arbitrary Lagrangian-Eulerian mesh displacement (ALE) with the code Cast3M. A comparison between the free response of an enclosed cylinder and an hexagonal prism was studied.…”

“…5. Numerical results for the tangential velocity u in both cylindrical and hexagonal geometries [13]. Comparison is given with the analytical solution of system 2 given in appendix (equation 9).…”