Ernst Grosse-Dunker
The Colebrook-White equation is the widely used basis for the calculation of the friction factor lambda for flows in pipes and ducts. Because this equation is implicit in lambda, many solutions have been developed to ease the calculation in order to reduce the effort and to reach a sufficient accuracy. Clamond has proposed in 2008 an iterative solution that requires maximally two iterations to obtain the machine double precision. Here an improvement of this solution is presented, that achieves already with one iteration a maximal error of 2.79E-7, what is more than sufficient for most engineering purposes. This solution is compared in a chart of CPU time versus accuracy with 28 solutions from the literature and in the group of the fastest solutions, that require only two calls of the logarithm function, it proved to be by far the most accurate one.