Interaction of Two Flapping Flags in Axial Flow

The flapping of two parallel flags in axial low turbulence flow is investigated experimentally inside a small scale wind tunnel test section. The variables of the problem are the size and flexural rigidity of the flags, and the distance that separates the two flags. The flow velocity represents the control parameter that governs the coupling and flapping mode of the flags. Two flapping modes, in-phase and out-of-phase modes, were observed in the experiment. Image processing technique was used and the time series of a given point on the flag edge was analyzed. The stability condition of the flags was obtained and compared to the recent theoretical models. The dynamics of the coupling between the two flags is also studied.