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

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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