Accelerating and Decelerating Flows in a Rod Bundle

Abstract

Hot-wire measurements of mean velocity and turbulence parameters were collected at the mid-point of a rod-wall gap and in the centre of a triangular subchannel in accelerating and decelerating flows through a large-scale (12.9:1) model of a 60\degree ~section of a CANadian Deuterium Uranium (CANDU) nuclear reactor 37-rod bundle. A method was developed to correct the axial velocity fluctuations for the effects of cycle-to-cycle variations, which were particularly significant during deceleration. Compared to values in stationary flows, the gap vortex street Strouhal number was slightly larger during accelerating flow and smaller during decelerating flow. The integral length scales of the axial velocity at both locations during both acceleration and deceleration were larger than the corresponding values in stationary flow. The Taylor microscale during transients was slightly larger than the stationary values. The turbulent kinetic energy dissipation rate was larger for accelerating flow and smaller for decelerating flow. The opposite was found to be true for the Kolmogorov microscale.