To elucidate the aerodynamic mechanism of galloping, the authors attempt another approach in the time domain relative to this oscillatory instability. As a test body, the present study takes up a square-section prism with a stationary long splitter plate in its wake. A black-box theory of galloping is presented. Wind-tunnel experiments are reported on the indicial pressure responses together with flow visualizations. The corresponding Reynolds numbers were approximately 1.9 × 104 and 8.9 × 103, respectively. In addition to the measurement of the indicial pressure responses, the sinusoidal pressure responses are also measured by forcedly oscillating the same model. As a result, the indicial body motion produces the separation-induced vortices on two sides parallel to the uniform flow, and these vortices are responsible for the lift force related to the onset of galloping. The quantitative agreement between theory and experiment is reasonable for slowly oscillating galloping.

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