Turbulent statistics and interface dynamics in a lubricated channel flow at $$Re_{\tau }=100$$

Abstract

AbstractIn this work we aim to study, through the use of Direct Numerical Simulations (DNS), the turbulent drag reduction (DR) that occurs in a lubricated channel during the transport of a fluid at a low Reynolds number. In this situation, one of the two fluids separates the second from the wall forming a thin layer in contact with it. In our configuration the thin lubricating layer is adjacent to one of the wall, which will be called lubricated side and and we consider the same density $$(\rho _1=\rho _2)$$ ( ρ 1 = ρ 2 ) for the two fluids, while for  the viscosity ratio $$(\lambda = \nu _1/\nu _2)$$ ( λ = ν 1 / ν 2 ) we will consider  two different values: $$\lambda = 1$$ λ = 1 and $$\lambda = 0.5$$ λ = 0.5 . Moreover to assess the role of the surface tension we have duplicated the two simulations at We number of $$We=0.055$$ W e = 0.055 and $$We=0.5$$ W e = 0.5 . As expected the DR mechanism is strongly related to the viscosity ratio, in particular the flow rate increase when decreasing $$\lambda$$ λ due to a relaminarization of the lubricated layer. Moreover, the parametric analysis on the effect of viscosity ratio and surface tension allows us to highlight very interesting modulations of the dynamics of the interface and of the turbulent kinetic budgets. To date, the latest studies in this area have been carried out using the Phase Field Method for the description of the interface. One of the scopes of the present study is to confirm and extend the existing results by exploring the dynamics of the flow with the use of the volume of fluid method.