Fluctuating Fluid Forces of Two Circular Cylinders in Parallel Arrangement at Close Spacing.

Abstract

This paper describes the results of an experimental study on characteristics of flow and fluid forces acting on two parallel circular cylinders. The Reynolds number was 5.5 × 104 on the bases of a single cylinder. For the spacing T/D<1.1 (T, spacing between the cylinders; D, diameter), the gap flow was biased to one side and intermittently changed over. When the spacing ratio between the cylinders was less than 0.3 the two cylinders formed a single wake behind them. The biased gap flow, for T/D=O.3∼1.1, formed a narrow wake with a Strouhal number higher than that of a single cylinder and a wide wake with a lower Strouhal number. In this region of spacing, when the gap flow switched spontaneously from one side to another, there existed another short duration stable flow (can be termed as intermediate flow) whose Strouhal number was almost equal to that of the single cylinder. The wavelet analysis of the velocity signals obtained with hot wire probes and flow visualization patterns confirmed the appearance of the intermediate flow pattern. Pressure and fluid forces acting the cylinder were decomposed for the narrow wake and the wide wake flow patterns, then fluid forces acting on the cylinders were explained on the basis of time-averaged and fluctuating pressure, fluctuating fluid forces, Strouhal number, and flow visualization.