Abstract
An experimental study is performed to determine the flow characteristics inside diamond-shaped cylinder bundles by means of two-dimensional particle image velocimetry (PIV) and two-dimensional laser Doppler velocimetry (LDV). Flow cross-sectional areas and flow rates are varied to change the Reynolds number on the flip-flop flows in the bundles. By means of PIV measurements, the velocity contours in divergent-region inside diamond-shaped cylinder bundles are disclosed to be symmetrical with respect the central, longitudinal dividing line, and the exsistence of "energy source point" is also disclosed from results of the equi-dU/dx distribution. The LDV is employed to measure velocity fluctuations in the flip-flop flow, while power spectra representing its oscillating characteristics are determined from LDV data. It is disclosed that the oscillation ratio of flip-flop flow and von Karman vortex street is about 1/20.
