Fluid Coupling Characteristics and Vibration of Cylinder Cluster in Axial Flow. Part II: Experiments

Abstract The vibration characteristics of cylinder clusters in turbulent axial flow are studied experimentally, and the measurements are compared predictions by the theoretical model in Part I of this study. Two-, four- and 28-cylinder clusters were tested, with a maximum of four flexible instrumented cylinders in the cluster, the rest being rigid. The vibration is displayed in terms of the PSD, coherence and CSD phase of the vibration signals from one or two neighbouring cylinders, in two orthogonal directions; also, in terms of r.m.s vibration amplitude and the coupled intercylinder patterns of motion. Agreement between theory and experiment varies from reasonably good to excellent, which provides support for the validation of the theoretical model. Certain general characteristics of the vibration, applicable to any cluster in axial flow were established, e.g., that the dominant frequencies of the turbulence-excited vibration are not associated with pure modal patterns (corresponding to the system eigenfrequencies): the dominant frequencies are not discrete, and the modal patterns evolve continuously with frequency. Furthermore, by (i) studying mixed flexible/rigid four-cylinder clusters, (ii) varying the intercylinder distances and (iii) comparing vibration of one-, two- and four-cylinder cluster, insight into the modal and spectral characteristics of such systems has been gained.