Coupled Vibration Research for Cylinders in Heat Exchanger Based on Noncontact-Measurement and Acoustic Fluid-Solid Interaction Simulations

A cylinder array vibrating in a fluid exhibits multiple coupled frequencies and coupled mode shapes. For a square array of four cylinders with a pitch-to-diameter ratio of 1.25, one cylinder was excited. In order to obtain the coupled modes of the whole array without the influence of exciters, a new method named noncontact-measurement image processing system was used in this paper. This system can guarantee the consistency of the frequencies quantificationally. Due to noncontact-measurement, the flow field around cylinder arrays will not be disturbed and can be measured precisely. Experimental results show that if we want to obtain all the coupled mode shapes, the consistency of cylinder frequencies (within 2%) must be insured and the vibrated cylinder should be chosen with larger amplitude in the coupled mode shapes. Distinct coupled frequencies correspond to symmetric mode shapes, while repeated coupled frequencies correspond to asymmetric ones. Besides, the acoustic fluid-solid interaction numerical method was used to calculate the vibration process of multi objects in still water. The numerical simulation results were in good agreement with experimental ones. It is found that for the same number of cylinders, the bandwidth of coupled frequencies increases with the decrease of pitch-to-diameter ratio, and that for the same pitch-to-diameter ratio, the bandwidth of coupled frequencies increases with the increase of the number of cylinders. Detuning of the cylinder frequencies leads to changes of coupled frequencies and coupled mode shapes.