Effects of Surfactant Additives on Flow Characteristics at Different Wall-Normal Locations in Turbulent Channel Flow

Large eddy simulation (LES) was performed for turbulent channel flow with and without surfactant additives at Re_τ = 590. Since turbulent channel flow can be divided into linear substrate layer, buffer layer, logarithm layer and outer layer along the wall-normal direction, so study on the flow properties at different layers in turbulent channel flow of viscoelastic fluid is significant for investigating turbulent drag-reducing mechanism and realizing the control of turbulent drag-reducing flow in the future. In this present work, the influences of surfactant additives on flow properties at different y locations were analyzed by researching the mean streamwise velocity, the root-mean-square velocity fluctuations, Reynolds shear stress and the contributions of different parts to turbulent kinetic energy, as well as the scaling law for four layers by two-dimensional wavelet transform. From the viewpoint of the above results, it is showed that the buffer layer tends to get wider in viscoelastic fluid and it is also demonstrated that viscoelastic effect mainly inhibits the coherent structures in the buffer layer, which are ejected from the linear substrate layer.