To identify drag reduction and phenomenon of multistage transition caused form addition of a minute amount of polymer in turbulent channel flows, a self-consistent linear effective viscosity model for stretching polymer was applied into the Navier-Stocks equations, and then polymer additive drag reduction effect is analyzed with the Reynolds stress equation model. The drag reduction percentage and transition points between adjacent drag reduction regimes are identified. The results are compared with direct numerical simulation and the feasibility of the effective viscosity model is validated. The usual turbulence statistics such as mean velocity profile, Reynolds stress, viscous stress and turbulence intensity in different drag reduction stages are discussed against the existing experimental and direct numerical simulation data. The characteristics of flow stability in the drag reduction stages are also clarified. These results can deepen understanding of turbulent drag reduction mechanisms and provide a guide for flow control.
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