The flow structure and force character of a flat plate in both pure harmonic oscillatory flow and in-line steady-harmonic combination flow have been investigated numerically by using the discrete vortex method. For the oscillatory oncoming flow case, when Kc number varies from 2 to 40, the vortex pattern exhibits a "harmonic wave"-like vortex-cloud, an inclined "harmonic wave"like vortex-cloud and a Karman vortex street, respectively. The calculated drag and inertia force coefficients varying with Kc number are in good agreement with Keulegan & Carpenter's experimental results (1958). For the combination flow cases, the vortex pattern also exhibits a vortex street, a "longitudinal wave"-like vortex-cloud and a cluster vortex-cloud corresponding to three typical in-line combination flow cases, i.e. Um/Uo=0(10−1), Ο(1) nd Ο(10), respectively. For small Kc number combination flow cases, it is further investigated for drag and inertia force coefficients varying with Kc number or with Um/Uo. The correlation of Cd with Kc, Um/Uo is given.
As the oncoming flow is oscillatory with various periods and amplitudes or is in-line combined by different steady oscillatory flow components, the flow structures and forces of the bluff bodies or of the flat plate will present a series of non-linear behaviors. As the subject is concerned, many investigations have been made by experiment and numerical simulation, and great success has been gained. Notahle amongst these are, Clements (1973), Sarpkaya (1975), Kamemoto & Bearman (1978), Kiya & Arie (1980), Graham, I (1982) and Chein & Chung (1988) for steady flow; Keulegan & Carpenter (1958, henceforth referred to as K&C), Graham (1982) and Lian (1988) for oscillatory flow; Armstrong & Barnes (1986), Griffin (1989) and Arai & Yamamoto (1988) for some combination flows whose focuses were on the vortex shedding lock-in phenomenon.
