沟槽表面边界层湍动能分布规律

 通过对不同风速下不同尺寸V型沟槽表面及光洁平板表面边界层内湍动能的测试,对比分析了沟槽表面边界层湍动能的分布规律。试验在一小型专用风洞中开展,流场测试中使用恒温式IFA300智能型流动分析仪,测试模型则采用有机玻璃材质的矩形平板结构;而在沟槽表面理论零点及壁面摩擦速度的计算中,采用基于湍流边界层Spalding壁面律公式同时计算壁面理论零点和壁面摩擦速度的改进方法。最终研究结果表明,沟槽结构主要影响边界层流场的近壁区,沟槽的存在提高了边界层中黏性底层内湍流脉动所具有的动能,有效降低了边界层中过渡区内的湍动能,最大相对降幅超过10%,较好地验证了基于“二次涡”的沟槽表面减阻理论。

Research on Characteristics of Turbulence Kinetic Energy in Boundary Layer over Riblet Surfaces

By performing a number of experiments on the turbulence kinetic energy of smooth plate surfaces and different V-riblet surfaces in various sizes at different wind velocities, the distributing rule of the turbulence kinetic energy over the riblet surfaces in the boundary layer is acquired. The experiments are carried out in a self-made special small-size wind tunnel. The flow field is tested with a TSI-IFA300 hot wire anemometer. The test models, which are made of organic glass, are so placed as to make sure the riblets are streamwise. In the calculation of the virtual origin and wall friction velocity of the riblet surfaces, a modified method is adopted, which can obtain virtual origin and wall friction velocity together by the least-squares fitting method based on the Spalding formula in the turbulent boundary layer. Ultimate results show that the existence of the riblets mainly change the near-wall flow field,and the turbulence kinetic energy in the viscous sublayer of the riblet surface boundary layer is increased, while the turbulence kinetic energy in the buffer zone of the riblet surface boundary layer is reduced dramatically,with the greatest relative reduction quantity of above 10%. This indirectly proves that the drag reduction mechanism of riblet surfaces based on the “secondary vortex” theory is reasonable.