Influence of tandem fluttering membranes on flow dynamics and heat transfer in turbulent channel flow

Abstract

The fluid–structure–thermal interaction of tandem fluttering membranes with gap distance ratios ranging from D*=1.0 to 4.0 in turbulent channel flow at Reynolds number ReL = 2.05×104 was investigated. Three distinct coupling modes (strong, medium, and weak, with D*=1.0, 1.5, and 2.0, respectively) of the tandem membranes were compared. The coupled fluttering motions and output voltages of the tandem membranes were recorded simultaneously. The two tandem membranes fluttered at the same frequency but different amplitudes. The flutter amplitude of the rear membrane, enhanced by the front membrane, exhibited the largest and smallest values in the strong and weak coupling modes, respectively. The phase difference Δϕ was linearly dependent on D*. Furthermore, the statistical flow quantities and heat transfer performance were examined. As D* increased from 1.0 to 2.0, only minor variations occurred in the streamwise and vertical velocities, leading to a decreased pressure loss and enhanced heat transfer. Moreover, the largest thermal enhancement factor was attained in the strong coupling mode owing to the large space-averaged Nusselt number. Finally, a membrane-shape-identification method was used to capture the spatiotemporal evolutions of the flow–structure dynamics. The decrease in the pressure loss and enhancement in the heat transfer of the tandem fluttering membranes were clarified by investigating the spatiotemporal evolutions of the unsteady flow behaviors. This study may offer an important reference for the designing of an efficient heat transfer device using multiple membranes.