肋条湍流减阻机理的研究

本文采用热线实验和大涡模拟数值计算方法,对三角形肋条的局部摩擦阻力和表面流场进行了测量和模拟,并对肋条的减阻机理进行了分析。结果发现,在整体减阻情况下,肋条表面局部摩擦阻力在展向位置分布不均匀,在肋尖附近区域为局部增阻区,在肋底附近为局部减阻区。在此基础上,通过涡动力学分析建立了局部摩擦力和流场涡运动之间的理论关系式,定量得出法向涡量和展向涡量的扩散流率是决定壁面摩擦阻力的两个因素。进一步研究发现,法向涡量和展向涡量的扩散流率主要集中在肋尖及其两侧,使得该区域能量输运和耗散强烈,形成局部增阻区。而在肋底附近,法向涡量和展向涡量的扩散流率较小,涡运动微弱,形成局部减阻区。

Investigation on Drag Reduction Mechanism of Riblets in Turbulent Flows

Hot-wire experiments and large eddy simulations were carried out to obtain the local skin-friction distribution and turbulent flows over triangular riblet,and the drag reduction mechanism of the riblet is investigated.The results show that under the overall drag reduction case,the local skin-friction distribution over riblet along the spanwise direction is not uniform.Based on this,two regions are defined,i.e.local drag increasing region near the riblet peak and local drag decreasing region near the riblet valley.Theoretical analysis conclude that the spanwise gradient and normal gradient of the spanwise vorticity axe two main factors in determining the local skin friction.Further study reveals that the spanwise gradient and normal gradient of the spanwise vorticity mainly concentrate near the riblet peak,which results in intense momentum exchange and energy dissipation.Thus,the wall skin-friction increases in this local region.Near the riblet valley,as the spanwise gradient and normal gradient of the spanwise vorticity is small and vortical motions are weak,the wall skin-friction decreases in this local region.