The drag reduction in laminar and turbulent boundary layers by prepared surfaces with reduced momentum transfer

Similarity solutions for laminar boundary layer tangential momentum accomodation coefficient (TAC) slip flow are presented showing that the efficiency of a given slip coefficient is pressure-gradient dependent. Turbulent boundary layer flow is calculated applying an integral method. Slip produces a sort of laminarization. It is confirmed that a given TAC-value in turbulent flow corresponds to a Kn number about one order of magnitude larger than in laminar flow. This effect depends on the ratio of laminar boundary layer to viscous sublayer thickness and is slip-coefficient-dependent. As the shear stress reductions in laminar and turbulent flow are equal, if the slip-coefficient is the same in both cases, in laminar flow a TAC-value of about 0.003 is needed for obtaining a reduction in friction loss of about 30%, while in turbulent slip flow a TAC-value of about 0.025 is necessary