THEORETICALLY BASED EXPRESSIONS IN CLOSED-FORM FOR THE LOCAL AND MEANCOEFFICIENTS OF SKIN FRICTION IN FULLY TURBULENT-FLOW ALONG SMOOTH AND ROUGH PLATES

The currently accepted correlating equations for the local and mean co efficients of skin friction in the turbulent boundary layer for unconf ined flow over smooth and rough plates are wholly empirical. Improved expressions in closed form in which the only empiricism is that arisin g from the generally accepted semitheoretical expressions for the velo city distribution, including the region of the wake, are derived herei n. These new, theoretically based expressions for the coefficients of skin friction are shown by comparison with experimental data to be mor e accurate for fully turbulent flow (Re(x) > 3 x 10(6)) than the previ ous empirical ones based on the same data and/or computed values. Exce pt for possible improvement of the numerical coefficients, these new e xpressions are not expected to be made obsolete by improved experiment al data or numerical solutions.