The effect of flow pulsation on drag and heat transfer in an array of heated square cylinders

Abstract

Laminar 2-D pulsating flow through homogeneous linear arrays of heated square tubes is simulated for pulsation frequencies of 0–80 Hz for tube diameter-based Reynolds numbers from 50 to 200. The objective is to examine the effects of flow pulsation on drag and heat transfer in heat exchanger tube bundles. Cycle-averaged and maximum drag coefficients, as well as the instantaneous and cycle-averaged Nusselt numbers are reported for each of the ten rows of tubes in the simulated array. The results show that flow pulsations can enhance heat transfer in tube bundles, and the level of enhancement increases with pulsation frequency and mean flow Reynolds number. A wake interference effect has been observed which significantly amplifies the drag on the leading rows and reduces and instantaneously reverses the sign of the drag force on the tubes located in the wake region. Cycle-average drag coefficients decreased with increasing Reynolds number and porosity, and were only a weak function of pulsation frequency. Peak drag coefficients were found to decrease with increasing Reynolds number and porosity, but increase with frequency approximately linearly. Empirical correlations are presented for a tube bundle with 64% porosity that relate maximum and cycle-average drag coefficients as well as Nusselt numbers to the Reynolds number and frequency.