Experimental Study on Effects of Blade Types of Passive Rotating Flow Turbulence Devices on Sediment Scouring and Silting

[Objective] To address the high cost and limited sustainability of conventional river-dredging techniques, this study proposes a novel, environmentally friendly, and energy-saving dredging approach—a pressure-difference-driven passive rotating flow turbulence device. It aims to clarify the mechanisms by which different blade types (curved, twisted, and flat) of the device affect local scouring and sediment transport, and to identify the blade type with the optimal scouring-silting performance, thereby providing an innovative technical method and structural optimization basis for targeted and directional river dredging. [Methods] The study was conducted through flume-based physical model experiments. Passive rotating flow turbulence devices with three blade types (curved, twisted, and flat) were designed and fabricated, with a single-pile device (without blades) as the control group. Tests were conducted under constant flow (13.62 L/s) and water depth conditions, with a movable bed paved using fine sand (median grain size d50=0.16 mm) having a gradation similar to the prototype sand of the Tarim River. Three-dimensional laser scanning technology was employed to accurately measure topography, and obtain the area, volume, and morphological characteristics of scouring and silting. An acoustic Doppler velocimeter (ADV) system was used to measure the time-averaged flow velocity and turbulence intensity distribution in the flow field around the device. By comparatively analyzing the scour hole development process, flow velocity field structure, turbulence characteristics, and final scouring-silting equilibrium state (with the scouring-silting ratio K as the core evaluation indicator), the dredging performance of devices under different blade types was assessed. [Results] The experimental results demonstrated that blade type significantly affected the device’s rotation characteristics, flow field disturbance capability, and ultimate scouring-silting performance. (1) Flow field characteristics: the curved-blade device achieved stable continuous rotation. Due to the Magnus effect, the main flow was noticeably deflected toward the side rotating with the current (right bank), with the bottom flow velocity at the right bank increasing by about 49.6% compared to the left bank, which effectively accelerated the initiation of bed sediments. The peak bottom turbulence intensity increased by about 89.47% compared to the flat-blade device, with the most intense flow field disturbance. The twisted-blade device rotated discontinuously, while the flat-blade device remained largely stationary. Both exhibited weaker flow field disturbance capability and less asymmetry than the curved type. (2) Scouring/silting morphology and performance: the curved-blade device yielded the highest scouring-silting ratio (K=94.6%), 48.5% and 16.3% greater than that of the twisted (K=46.1%) and flat (K=78.3%) types, respectively. The curved blade produced a distinctly asymmetric scour hole biased toward the right bank, with a large affected area and an interwoven pattern of scouring and silting zones, which facilitated downstream sediment transport. (3) Scour hole development: the scouring process could be divided into four stages: initial, transition, disturbance, and stabilization. The curved-blade device exhibited the fastest scour-depth development rate across all stages, particularly during the disturbance stage (device rotating continuously), efficiently disturbing bed sediments and enlarging the scour hole. [Conclusion] Among the passive rotating flow turbulence devices, the curved blade demonstrates the best comprehensive performance in scouring and sediment transport, owing to its ability to induce stable continuous rotation, produce a significant Magnus effect, and maximize the enhancement of bottom turbulence and flow velocity deflection, with a scouring-silting ratio significantly higher than other types. The device has a simple structure and requires no external power, offering a novel, environmentally friendly, and energy-saving approach for targeted river dredging. The findings clarify the critical influence of blade type, thereby providing a direct theoretical and experimental basis for further optimization of the device’s structural parameters and engineering deployment schemes.