Abstract
Time-averaged quasi-static forces are significant in the study of the fluidelastic instability of tube arrays. Furthermore, measuring the fluid force phase from the unsteady force measurements could be used to directly investigate the dynamic behaviour of an array and predict the array instability onset. Force measurements were previously performed for a rotated triangular array with spacing ratio P/D = 1.5. In this paper, a more compact rotated triangular array is studied following the same measurement approach. This rotated triangular array has a pitch ratio P/D = 1.33. Determining the relationship between the fluid force coefficients used in the quasi-steady model, and fluid force phase used to predict the fluid damping, is one of the main objectives of this work. This is in order to relate the fluid forces to the array pitch spacing. This should be a step toward generalizing the quasi-steady model for the rotated triangular array for various pitch ratios. In this paper, the quasi-static fluid forces are measured in single phase (water) and two-phase (air-water) cross flow in the streamwise direction. The quasi-steady model is then solved, using the forces, to predict the fluidelastic instability onset of the array. Model results are also directly compared with vibration experimental results.
