2007 Volume 2 Issue 2 Pages 480-489
The mechanism of secondary flow was discussed based on a result of LES of turbulent flow in a subchannel. The LES was carried out on the Cartesian grid system using an improved immersed boundary method developed for accurate simulation of complex wall boundary of industrial interest. The method was verified by comparing the LES with a DNS of turbulent flow in a pipe. The LES for the subchannel reasonably reproduced the secondary flow of the second kind. To analyze the mechanism of the secondary flow, a theoretical method was proposed. The result of the analysis indicated that main source of the secondary flow was a non-conservative component of Reynolds stress as was the case for a square duct. The theory suggested that the non-conservative force corresponds to an imbalance between pressure along the wall and Reynolds stress decreasing rapidly near the wall. The present theory will unify an understanding between secondary flows of the first and second kind. The present LES technique and theory are useful for investigating physics in turbulent flow bounded by complex walls.
