Abstract
The overall efficiency of high-speed rotating machines depends largely on their mechanical efficiency. Mechanical efficiency is not just a matter of bearing losses, but includes all interactions of the rotor with the environment. Analytical and empirical descriptions of turbulent or laminar flow around rotating surfaces have been used to estimate the mechanical losses of a turbocharger rotor based on geometric parameters and operating conditions. Based on the knowledge of the effect of each parameter, design changes to the rotor were proposed. The positive effect of simple design modifications on mechanical losses was experimentally verified by measurements on a test turbocharger.