截面形状对疏水性微肋阵内减阻特性的影响

在截面为圆形、菱形和椭圆形微肋阵内涂覆不同性能的疏水性涂层,形成疏水性微肋阵。去离子水在疏水性微肋阵内表面的接触角分别为99.5°、119.5°和151.5°。测试去离水以不同流速流经疏水性试验段流道内压力降和摩擦阻力系数。试验结果表明,在相同的接触角和流量下,圆形微肋阵内压力降最高而椭圆形最低;当接触角为99.5°,雷诺数Re低于600时,椭圆形微肋阵内减阻率要高于菱形和圆形微肋阵,当Re600时前者要低于后两者。随着接触角的增大,圆形内减阻率要明显高于菱形和椭圆形微肋阵,菱形和椭圆形微肋阵在低Re下较为接近,在高Re下前者的减阻率要高于后者;表面疏水性处理能够显著降低摩擦阻力,同时推迟流动分离和尾流区转捩,因此对于分离较早、压差阻力较大的微肋阵的减阻效果更加明显。

Characteristics of Drag Reduction in Different Cross Sections of Hydrophobic Micro Pin Fins

The hydrophobic coatings with different properties are coated on the surfaces of micro pin fins with different cross section of circular,diamond and elliptical,respectively,and hydrophobic micro pin fins are formed.The contact angle of the deionized water on the surface of hydrophobic micro pin fins is 99.5°,119.5° and 151.5°,respectively.The pressure drop and the friction resistance coefficient are measured experimentally when water flow through the hydrophobic micro pin fims at different flow rates.Experimental results show that the pressure drop in the circular micro pin fins is highest and the ellipse is minimum at the same contact angle and flow rate,and the frictional resistance coefficient in ellipse micro pin fins is higher than that in diamond and circular micro pin fins when the contact angle is 99.5 degrees and Reynolds number Re is less than 600;however,the former is lower than that of the latter two when Re＞600.The resistance reduction rate of circular micro pin fins is higher than that of the diamond and ellipse micro pin fins with the increase of the contact angle and those of the diamond and the ellipse is close at low Re,but the diamond is higher than the ellipse at high Re.The surface hydrophobic treatment can significantly reduce the friction resistance,at the same time it delay flow separation and the transition from laminar flow to turbulent flow at the wake,so the resistance reduction effect of micro pin fins is more obvious for the earlier separation and the lager differential pressure resistance.