In-flow Stability and Flow Drag Reduction Performance of Resident Electrolyzed Microbubble Array

Aiming at the problem of stable high-efficiency underwater drag reduction for the vehicle surface, an experimental study on the flow drag reduction performance of autostable electrolyzed microbubble array was carried out. The test piece of electrode-wall micropore array capable of forming the stable microbubble array air film through electrolysis was prepared, revealing the mechanism of electrolysis voltage, micropore size, flow velocity affecting the growth behavior and resident stability of electrolyzed microbubbles, and the flow drag reduction performance and mechanism of microbubble array were investigated by the experimental and numerical methods. The research results indicated that the electrode-wall micropore could realize the self-adaptive start-stop control of microbubble electrolysis; the time for the microbubble to reach stable diameter was shorter, but the resident time and rate of the microbubble array would decrease under the higher electrolysis voltage; the resident time and rate of the microbubble array were greater, and the time for the microbubble to reach stable diameter was shorter for the 250 µm micropore; the microbubble array’s average drag reduction rate was about 23%, and the maximum resident time and rate were 420 s, 95.46%, respectively, for the 250 µm micropore when the voltage was 20 V; the resident microbubble deformation and the air/water interfacial force jointly caused a large amount of upward throwing high-speed flow above microbubbles, which suppressed the down-sweep flow burst of flow direction vortices, and significantly reduced the near-wall Reynolds shear stress; the microbubble array near-wall numerical average kinetic energy was about 0.010 m2/s2 less than that of pure flat plate (about 0.021 m2/s2), the microbubble array numerical average wall shear was about 30 Pa less than that of pure flat plate (about 55 Pa), thus the high-efficiency turbulent drag reduction was achieved. © 2022 Editorial Department of Journal of Sichuan University. All rights reserved.