A PARAMETRIC STUDY OF THE RESONANCE MECHANISM OF TWO TANDEM CYLINDERS IN CROSS-FLOW

摘要

A parametric study has been performed to investigate the effect of cylinder diameter on the acoustic resonance mechanism of two tandem cylinders exposed to cross-flow in a duct. Three spacing ratios corresponding to different flow regimes inside the "proximity interference" region are considered, L/D = 1.5, 1.75 and 2.5, where L is the spacing between the cylinders and D is the diameter. For each spacing ratio, six cylinder diameters in the range of D = 7.6 mm to 27.5 mm, have been tested. For small diameter cylinders, the acoustic resonance mechanism of the tandem cylinders seems to be similar to that observed for single cylinders. However, for larger diameter cylinders, the resonance of a given acoustic mode occurs over two different ranges of flow velocity. The first resonance range, the pre-coincidence resonance, occurs at flow velocities much lower than that of frequency coincidence. The second resonance range, the coincidence resonance, is initiated near the condition of frequency coincidence. Thus, the occurrence and the intensity of the pre-coincidence resonance are found to be strongly dependent on the diameter of the cylinders. It is shown that increasing the cylinder diameter affects several flow parameters, which make the tandem cylinders more susceptible to the pre-coincidence acoustic resonance.