Bistable features of the turbulent flow in tube banks of triangular arrangement

Abstract

In the present work, some features of the turbulent flow in tube banks of triangular arrangement are discussed. The experimental study is performed by means of hot-wire measurements in an aerodynamic channel, and flow visualizations in a water channel. The tube banks had pitch-to-diameter ratio 1.26 and 1.6, and the Reynolds numbers are in the range from 7.5×103 to 4.4×104, computed with the diameter of the tubes and the percolation velocity. The experimental data are analyzed through statistical, spectral and wavelet tools. The results show stable wake patterns after the first row of tubes. Visualizations show that the flow which arises from the gap between the tubes form coalescent jets. In some cases, a changing flow direction occurs. This phenomenon is called in the literature as “metastable”. After two rows of tubes, the flows present a transverse vertical component. For P/D=1.26, the flow direction changes at irregular time intervals, called “bistable flow”. For P/D=1.6, the wake pattern is stable. The features of turbulent flow through three, four and five rows of tubes seems to be similar, where the gap flop presents a fast swapping, from one side to another (flip-flop).