Effects of low-Re pulsatile flow on friction characteristics in bare square array rod bundles

Interest in unsteady flow in floating systems has increased in recent times. This paper presents the results of the experimental investigation on the resistance characteristics of pulsating flow through square array bare rod bundles with P/D = 1.326 and W/D = 1.268 conducted in the range of time-averaged Reynold's number Reta = 1-7 × 103 and dimensionless acceleration (α) of 0.001-0.013. Pulsatile flow affects the time-averaged friction factor because it changes the velocity field close to the wall. The dimensionless frequency parameter (ω′) relates the frequency to the viscous effects while the dimensionless acceleration (α) is the product of the velocity amplitude (Au), diameter (D) of the channel and the frequency (ω) normalized by the mean velocity (Um). Ratios (Cλ) of the time-averaged friction factor (λp) in pulsatile flow to the friction factor (λs) in a steady flow and (Cp) of their average pressure drops were used to compare the two flows. Cλ and Cp increase with an increase in Au, ω′ and α; but decreases with increase in Reta. The dynamics of the extra turbulence generated as a result of pulsation was also analyzed in the subchannels.