Drag reduction mechanism of blade with non-smooth surface in hydraulic pressure recovery turbine

The Hydraulic Pressure Recovery Turbine (HPRT) is a liquid pressure recovery device that plays a crucial role in enhancing efficiency, reducing costs, conserving energy, and achieving emissions reduction in process industries. To improve the hydraulic performance of the HPRT, this study employs non-smooth surface microstructures in the blade design for drag reduction, based on its energy dissipation characteristics. The effects of different microstructural units on hydraulic performance and their drag reduction mechanisms are explored. The results show that, under low-flow conditions, the hydraulic performance of the microstructures decreases. However, under design and high-flow conditions, efficiency improves significantly compared to the original model. Among the microstructures, the V-shaped microstructure demonstrates the most notable effect, with a roughly 2% increase in efficiency under design conditions. The mechanisms underlying the microstructures' effects are primarily reflected in two aspects: first, they suppress the formation of separation vortices on the pressure surface of the blades, reducing energy losses within the impeller; second, the microstructures generate secondary vortices that oppose the flow direction in the near-wall region. These vortices interact with the main flow, facilitating momentum transfer and broadening the low-speed flow region near the wall. This reduces the velocity gradient, thereby decreasing Reynolds stress and viscous resistance. Additionally, the reverse vortices within the microstructures function like “rolling bearings,” converting sliding friction into rolling friction, further reducing frictional resistance.