The Attenuation of Flow-Induced Vibration of a Staggered Cylinder Pair With the Use of Perforated Splitter Plates

The use of perforated splitter plates for the suppression of flow-induced vibration of twin cylinders in a staggered arrangement subjected to cross flow was examined experimentally. The center-to-center spacing of the cylinders was 3.0 cylinder diameters in the streamwise direction and 0.5 cylinder diameters in the transverse direction, a spacing that is known to possess large variations in transverse force coefficients with small transverse displacements. The experimental arrangements consisted of two spring mounted cylinders, and included the following specific cases: no splitter plate, splitter plate attached to the trailing edge of the upstream cylinder, splitter plate attached to the leading edge of the downstream cylinder. The splitter plates were perforated (40% open area ratio, 3/8 inch holes) and were rigidly attached along the entire length of the cylinder parallel to the mean flow. The splitter plates were 1.3 diameters in the streamwise extent Amplitude and frequency of the vibrations of both cylinders were measured as a function of reduced velocity (UR=U/fc*D where U is the free stream velocity, fc is the natural frequency of the cylinder in a motionless fluid, and D is the cylinder diameter). Results show that for the configuration in which the perforated splitter plate is attached to the trailing edge of the upstream cylinder, the vibrations due to the jet-switching mechanism are eliminated at low reduced velocities (UR<240), and the amplitude of vibration was significantly reduced at higher reduced velocities. The configuration in which the splitter plate is attached to the leading edge of the downstream cylinder did not attenuate the vibrations; however, this configuration did exhibit interesting behavior. At a reduced velocity of about 240 the jet-switching mode of excitation (the cylinders move out-of-phase with each other) suddenly stopped, and no vibration at all was present for an intermediate range of reduced velocities (240<UR<280). At reduced velocities above 280 the vibrations began again; this time in the galloping mode (the cylinders move in-phase with each other). Preliminary results for the configuration in which the splitter plate was attached to the trailing edge of the downstream cylinder show that this configuration has no significant effect on the vibrations.