#ifndef FRICTIONFACTOR_HH #define FRICTIONFACTOR_HH #include #include #include #include "constants.hh" // ReL, ReT #include "fade.hh" inline double frictionfactor(const double Re, const double r) { if (0.0 == Re) { return 0.0; } else if (ReL >= Re) { // laminar flow return 16.0 / Re; // using k = 4.f.(l/d) } else if (ReT <= Re) { // turbulent flow /* S.E.Haaland * Simple and explicit formulas for the friction factor in turbulent pipe flow * Journal of Fluids Engineering, 105 (1983) */ double A = 6.91 / Re; double B = pow((r / 3.71), 1.11); double f = pow(-3.6 * log10(A + B), -2); return f; } else { // transition region double ffL = frictionfactor(ReL, r); double ffT = frictionfactor(ReT, r); return fade(Re, ReL, ReT, ffL, ffT); } } #endif // FRICTIONFACTOR_HH