1998 年 64 巻 627 号 p. 3590-3596
Prevention of vibration and acoustic resonance, originating in cross flow through the tube banks is important for a heat exchanger such as boiler. This paper is concerned with the excitation mechanism of velocity fluctuation in the tube banks which are arranged closely together. We measured the volocity fluctuation in a closely staggered arrangement. The ratio of Ion-gitudinal pitch to rod diameter of this arrangement was varied in a range of L/D=1.1 to 1.5, while the traverse spacing ratio is fixed at T/D=2.0. The range of Reynolds number is from 0.33×104 to 6.6×104. There are three dominant frequencies in the flow, caused by the different mechanisms : the fluctuation of flux which are flow rate fluctuations due to periodical change in the reattaching point, the change of the flow pattern in the separation region and the vortex shedding. The fluctuation of flux and the change of flow pattern have strong influence on the flow, and dominance in the two mechanisms changes with Reynolds number and the longitudinal spacing ratio.