AN EXPERIMENTAL-STUDY ON THE FLUIDELASTIC FORCES FOR 2 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 ci rcular cylinders, of equal diameter, in air cross-flow, for 10 differe nt geometrical arrangements. One cylinder is forced to oscillate trans versely to the flow, while the other cylinder remains stationary, and measurements are made either on the oscillating or the stationary cyli nder. The forcing frequency, f, is varied from 1 to 16 Hz, with a fixe d 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), respe ctively, for the force- and pressure-based experiments. The free-strea m 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 domain s, respectively. The amount of hysteresis in the dynamic force coeffic ients 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/f D is reduced below a critical value. This critical value of U/fD is ve ry sensitive to the geometrical arrangement of the two cylinders: it i s large when the cylinder is in a sensitive region (where there are ra pid changes in static force coefficient with cylinder displacement), a nd it is much smaller away from these regions. (C) 1998 Academic Press Limited.