Energy consumption characteristics in fully-developed slot flow with moving boundaries

Critical energy efficiency is often required in the fluid-structure interaction with the moving boundaries—such as hydraulic machinery, turbomachinery, and plunge pools. However, the previous research has focused primarily on the flow field identification. This work aims to specifically target the underexplored link between turbulent structures and energy dissipation. A systematic investigation was made on the energy consumption characteristics of the fully-developed slot flow under high Reynolds number (Re) conditions. Physical experimentation and theoretical analysis were employed for the hydrodynamic similarity and measurement accuracy. A scaled model consisted of an organic glass plate (2000 mm × 50 mm × 30 mm) translating uniformly within a 9 m long rectangular acrylic pipe (cross-section: 50 mm × 50 mm) at four controlled speeds (0.1, 0.2, 0.3, and 0.4 m/s). The flow regime was maintained at Re = 15000-22176 (all turbulent) with a fixed slot ratio (Ψ = 0.4). While Particle Image Velocimetry (PIV) was captured the instantaneous velocity fields, and high-speed cameras were used to track the plate kinematics. Furthermore, water temperature was stabilized at 27-28 °C for the viscosity consistency during experiments. The energy dissipation was obtained to quantify the turbulent kinetic energy, vorticity distributions, and viscous energy losses. At the same time, the energy loss from the moving boundary was analyzed to evaluate boundary effects using the velocity ratio (K=v_c/v_a, where va was the average slot flow velocity). Energy-saving efficiency (η = v_c/Q_d, with Q_d as energy loss per unit area and distance) was also introduced for quantitative evaluation. The results revealed that: 1) Turbulent kinetic energy near the moving plate boundary consistently exceeded the levels near static pipe walls, indicating the dominant role of boundary motion in energy transfer. The intensity of turbulent kinetic energy increased significantly by 80.6%-119.9%, as both Reynolds number and plate velocity rose. Boundary motion outweighed Reynolds number near localized high-shear regions. 2) Vorticity analysis demonstrated that the distribution exhibited symmetrically opposite values (ranging from -10 to 10 s⁻¹) around the pipe’s longitudinal central axis. Critically, the large-scale vortices near the pipe center (occupying 43%-66% of the slot area) caused the minimal energy loss, due to the weaker rotational intensity, whereas the small-scale vortices near the walls (12%-20% of the area) were induced substantial energy loss as a direct consequence of intense, localized rotation and momentum exchange. In energy dissipation dynamics, the energy loss from the moving boundary first decreased and then increased with the velocity ratio K, reaching the minimum when K=1.0. The wall shear stress was minimized, when the plate and flow velocities were nearly equal, effectively reducing viscous drag. 3) Reynolds number increments amplified the energy loss to thin the viscous sublayer, consequently increasing near-wall velocity gradients. Importantly, the quantitative assessment of efficiency revealed that the maximum wall energy-saving efficiency η, 1.72, occurred at Re=15 000, v_c=0.3 m, indicating a 43.33% improvement over the suboptimal condition (Re=15000, v_c=0.4 m/s, η=1.2) with an optimum for operational parameters. The energy consumption of slot flow with moving boundaries was determined with the relationships between turbulent kinetic energy, vorticity distribution, and energy loss. The energy-saving efficiency and identification of the optimal velocity ratio (K=1.0) can provide a practical reference to optimize the high-Reynolds-number fluid-structure interaction, particularly in the operation of hydraulic machinery and water conservancy structures. These insights ultimately facilitate the energy efficiency and operational stability using target control of near-wall turbulence and vortex-induced dissipation.