On the mechanism and prediction of the drag reducing turbulent flow by Toms effect

由链状聚合物分子或表面活性剂形成棒状胶束而引起的减阻现象称为汤姆斯效应。我们建立的哑铃形微小离散元模型模拟了链状高分子和表面活性剂。我们假设该单元在介质波动和模拟表面活性剂添加剂流动的情况下处于平衡状态。在我们以前的研究（1）中，我们提出了37%的减阻可以通过二维湍流通道流动的直接数值模拟（DNS）来重建。从这些结果中，我们认为，该单元削弱了与雷诺应力产生有关的近壁面纵向涡，从而可能导致减阻。在本研究中，我们使用我们的模型重建减阻现象，并观察元素和纵向涡之间的相互作用，通过流动显示AVS/AVS6.1。在此基础上，对纵向涡的衰减和减阻现象进行了机理研究，并在模型中加入了哑铃形单元，模拟了聚合物在流体中的拉伸力作用下被剪切的特性。对Re_τ=120-600的二维槽道流动进行了数值模拟，并再现了减阻率达70%的减阻效果

The phenomenon of the drag reduction caused by chain polymer molecule or the surfactant which forms the rod-like micelle is known as Toms effect. Our minute discrete element model like dumbbell simulates chain polymer molecule and surfactant. We assumed that the element was in equilibrium for fluctuation of medium and modeled surfactant additive flow. In our previous research(1), we represented the 37% drag reduction can be reconstructed through Direct Numerical Simulation (DNS) of two-dimensional turbulent channel flow. From these results, we consider that the element weakens the longitudinal vortices near wall surface which are bound up with Reynolds stress production and then drag reduction may be caused. In this research, we reconstruct drag reduction phenomenon using our model and observe the interaction between elements and longitudinal vortices by flow visualization using AVS/Express6.1. Then examinations of the mechanism of drag reduction phenomenon and longitudinal vortices decay based on these databases are carried out.In addition study, new character is added on the model, say, the dumbbell element which simulate a polymer can be cut by the stretching force in the fluid. Simulations of 2D channel flows (Re_τ=120-600) are carried out and the drag reduction up to 70% drag reduction rate is reproduced by the modified model