Johann Nikuradse – Hydraulic experimenter

Hydraulic engineers are familiar with the Nikuradse sand-roughened pipes, the "Nikuradse harp" describing the friction coefficient of pipe flow, and the Nikuradse plots showing data points almost perfectly arranged along a curve. Who was Nikuradse, a collaborator of Ludwig Prandtl from Göttingen University? How did Nikuradse work, and where did he finally move? This paper retraces the career and life of a person whose name is widely known in hydraulic engineering, but whose person has been obscured by the complicated European history from 1900 to 1950. Recently located documents shed additional light on the "Nikuradse case".