An experimental study on the fluidelastic forces for two staggered circular cylinders in cross-flow

Both pressure distribution and force measurement techniques have been employed to measure the fluidelastic forces on one of two staggered circular cylinders, of equal diameter, in air cross-flow, for 10 different geometrical arrangements. One cylinder is forced to oscillate transversely to the flow, while the other cylinder remains stationary, and measurements are made either on the oscillating or the stationary cylinder. The forcing frequency, f, is varied from 1 to 16 Hz, with a fixed half peak-to-peak amplitude of 0.043, 0.047 or 0.17 D; the cylinder diameter, D, is fixed at 48.7 mm (1.9 in) and 114.3 mm (4.5 in), respectively, for the force- and pressure-based experiments. The free-stream velocity, U, is varied from 10 to 35 m/s, and this leads to 4 x 10(4) less than or equal to Re less than or equal to 2 x 10(5) and 15 less than or equal to U/fD less than or equal to 300. Pressure- and force-based measurements are post-processed in the time and frequency domains, respectively. The amount of hysteresis in the dynamic force coefficients versus cylinder displacement plots increases significantly with decreasing U/fD. The corresponding magnitudes and phase angles of the fluidelastic forces depart rapidly from the asymptotic values when U/fD is reduced below a critical value. This critical value of U/fD is very sensitive to the geometrical arrangement of the two cylinders: it is large when the cylinder is in a sensitive region (where there are rapid changes in static force coefficient with cylinder displacement), and it is much smaller away from these regions. (C) 1998 Academic Press Limited.