亲水-超疏水相间表面通气减阻实验研究

EXPERIMENTAL STUDY ON DRAG REDUCTION BY AIR INJECTION ON HYDROPHILIC AND ALTERNATED SUPERHYDROPHOBIC SURFACES

超疏水表面有利于在壁面形成气膜层,是一种潜在的兼具防污功能的新式仿生减阻技术,但在高速来流的剪切作用下该气膜易流失破坏.通过构造亲水-超疏水相间表面来增强超疏水表面气膜层的稳定性,从而期望达到更优的减阻效果.采用重力式水循环管道测试系统,测试了在湍流状态下,超疏水条带宽度与雷诺数对减阻效果的影响,并分析了对应的气膜铺展状态及其对减阻特性的影响.结果表明,亲水-超疏水相间表面持续通气能解决表面气膜层的流失问题,实现气膜层的长时间稳定维持;表面减阻率随水流速度(雷诺数)的增大呈现降低趋势,且表面气膜稳定性逐渐降低;表面减阻率随超疏水条带宽度增加呈现出先增后减的趋势,并在超疏水条带宽度为5.0 mm时达到最大,最大减阻率为40.2%.分析原因在于,超疏水条带较窄时,高剪切应力的液固界面占比较高,带来了较高的阻力;而条带较宽时,表面气膜层稳定性不佳.因而在某一流动状态下,存在最为合适的超疏水条带宽度,使得减阻效果最佳.

The superhydrophobic surface is conducive to the formation of gas film on the wall,which is a potential new bionic drag reduction technology with potential anti-fouling function.However,the gas film is easy to be lost and damaged under the shear action of high-speed incoming flow.By constructing the hydrophilic and alternated superhydrophobic surfaces to enhance the stability of the superhydrophobic surface gas film,thus expect to achieve a better drag reduction effect.Using a gravity type water circulation pipeline testing system,The influence of superhydrophobic strip width and Reynolds number on drag reduction performance under turbulent conditions were tested.In addition,the corresponding gas film spreading state and its impact on drag reduction characteristics were analyzed.The results show that the continuous air injection of the hydrophilic and alternated superhydrophobic surfaces can solve the problem of the loss of the air film layer on the surface and realize the stable maintenance of the air film layer for a long time;the surface drag reduction rate shows a decreasing tendency with the increase of the water flow rate(Reynolds number),and the stability of the surface air film layer decreases gradually;the surface drag reduction rate shows a tendency of increasing and then decreasing with the increase of the width of the superhydrophobic strips and reaches a maximal reduction rate of 40.2%at the width of the superhydrophobic strips of 5.0 mm.The reason for this is that when the superhydrophobic strip is narrower,the liquid-solid interface with high shear stress accounts for a higher percentage,which brings a higher resistance;and when the strip is wider,the stability of the air film layer on the surface is not good.Therefore,the most suitable width of superhydrophobic strip exists under a certain flow condition,which makes the best drag reduction effect.