Flow measurements in rod bundle subchannels with varying rod-wall proximity

Abstract

Detailed measurements of fully developed, turbulent, air flow through a five-rod sector of a 37-rod bundle have been conducted for the design geometry of the bundle, as well as for several cases with the central rod displaced towards the external tube wall and/or towards a neighboring rod, including cases with rod-wall and rod-rod contact. The wall shear stress on an outer rod reached minima at rod-wall and rod-rod gaps and maxima at open flow regions. The average and the minimum wall shear stresses decreased dramatically only for very small values of the rod-wall gap. Measurements of the mean velocity, Reynolds stresses and turbulent scales in the wall and inner subchannels are presented mostly as iso-contours. Isotachs bulged towards narrow gaps and corners, with the bulging becoming more pronounced as the rod-wall gap decreased. The local friction factor not only varied appreciably around the rod as the gap decreased, but also had values much larger than the average friction factor based on the subchannel bulk velocity, due to the variability of the local flow width.