Tiny Tesla Turbine Analytical Performance Validation Via Dynamic Dynamometry

Abstract

Tesla turbines produce power at high rotation rate and low torque relative to other prime movers. At a tiny scale, this attribute renders Tesla turbines poorly matched to dynamometers designed to characterize electricand gasoline-powered radio-controlled vehicles and kit cars. Techniques are needed to enable Tesla turbine design and performance evaluation. An analytical modelling approach was recently developed by Carey, and a complimentary experimental technique, dynamic dynamometry, can determine Tesla turbine power curves without a dynamometer. This paper mutually validates these approaches by comparing them to each other using results from a 3D printed 4-disk tiny Tesla turbine with characteristic disk inner/outer diameter of 11.54 ± 0.01 mm and 24.85 ± 0.01 mm respectively. The Carey model predicts maximum power output of 0.077 ± 0.015 W, and dynamic dynamometry predicts 0.122 ± 0.008 W, a 36.9% difference. Bounding assumptions were used and more accurate parameter measurements will drive these values closer together. Peculiarities of tiny Tesla turbine operation are also described, including the discovery that turbine spin-down rotational velocity is not linear with time. This phenomenon is likely caused by fluid boundary layer shear between the housing and outer disks. It is not observed in larger Tesla turbines, suggesting a speed, size and/or disk count threshold at which this phenomenon introduces non-trivial parasitic reduction in performance.