Effects of rolling on resistance characteristics of single-phase flow in a 3 × 3 rod bundle

Experimental investigations on resistance characteristics of single-phase water flow in a 3 × 3 rod bundle subjected to the rolling motion were performed. The mean Reynolds number ranged from 174 to 15,137, and the rolling period and amplitude ranged from 8 s to 16 s and from 5° to 15°, respectively. The results show that the rolling motion has no significant influence on mean frictional coefficient and local resistance coefficient. The growth rate of local pressure drop with flow rate is much higher than that of frictional pressure drop. The frictional and local pressure drops fluctuate significantly on the whole range of flow regime, and their fluctuation amplitudes gradually increase as the mean Reynolds number increases. The amplitude of relative frictional pressure drop increases with increasing the rolling amplitude, while it is nearly invariable with rolling period. However, the rolling motion nearly has no effect on the amplitude of relative local pressure drop and only changes its fluctuation period in such a limited variation of rolling conditions. New correlation for predicting transient frictional coefficient is developed by multiple regression by considering the influences of rolling motion as well as flow conditions.