ICONE19-43569 STUDY ON FLOW INDUCED VIBRATION EVALUATION FOR A LARGE SCALE JSFR PIPING : (4) UNSTEADY FLOW CHARACTERISTICS IN 1/10 SCALE HOT-LEG PIPING EXPERIMENTS UNDER UNDEVELOPED AND SWIRL INFLOW CONDITIONS

Abstract

LDV measurements in a 90 degrees elbow were examined for the cases of inflow from a long pipe, short pipe and swirl generator. The elbow is considered as a 1/10 scale hot-leg piping model of a Japanese sodium-cooled fast breeder reactor (JSFR). Time-averaged flow distribution for the Reynolds number of 320000, based on the inner pipe diameter and bulk velocity, shows that shortening the upstream pipe length to 4.9D from 10D induces the flow separation downstream of the elbow. Detailed observation shows that shortening upstream pipe weakens the Prandtl's secondary flow of the first kind. This suppresses the kinetic energy transport from the outer to inner side of the elbow. Swirl generator in the present experimental setting generates the swirling inflow with the non-dimensional angular momentum of 0.12, based on the inner pipe diameter and bulk velocity. The circumferential velocity distribution formed a shape like Rankin's combined vortex in the elbow inlet, and the accelerated axial velocity at the vortex center is observed. The axial velocity distribution however is found to be almost the same as that of the non-swirl inflow case in the latter half of the elbow. Frequency analyses shows that the Strouhal number by vortex shedding from the boundary layer occurring at the inner side became 0.5, except for 0.6 in the case of the long pipe case. This might be related with the boundary layer width and the local flow velocity.