Session: 08-08-02: Design Analysis and Optimization of Energy Conversion Systems - 2

Paper Number: 137261

137261 - Horn-Shaped Tesla Turbines: Experimental Output Power Comparison With a Conventional Bladeless Design Using Air as the Working Fluid 

Tesla turbines are a simple and compact means of power conversion which offer a reliable and cost-effective alternative to conventional bladed turbines. These turbines use viscous drag forces caused by the passage of a fluid through tightly spaced disks to function, as opposed to bladed turbines, which take advantage of flow constriction by means of blades or shaped passages to produce hydrodynamic pressure on the blades to spin the rotor. The conventional Tesla turbine rotor consists of several thin, flat disks mounted on a shaft. The rotor, by means of bearings and seals, is enclosed within a housing. Fluid enters the housing through a nozzle which directs its trajectory to be perpendicular to the outer surface of the rotor. As momentum is exchanged between the fluid and the rotor, the fluid loses energy and follows a spiral trajectory to the exit ports at the center of the rotor. The change in direction caused by the right-angle trajectory of the fluid at the outlet ports of the turbine disks is a significant source of energy loss. 

 

The primary goal of this article is to introduce the design of horn-shaped Tesla turbines and present the turbine efficiency and power output results obtained from an experimental comparison between them and conventional planar Tesla turbines. Modifying the geometry to be horn shaped reduces the losses caused by the right-angle exit trajectory at the turbine's outlet port common to planar Tesla turbines. Patents discussing the use of modified impeller geometries for exit loss reduction due to direction change have been previously published. These patents include the design of a variable spacing curved disk impeller for pump applications, and the design of a conical disk bladeless turbine. However, no literature was found to show power output measurements for curved disk impellers used in turbine applications and compare performance with their flat disk counterpsarts. 

 

The paper outlines the procedure for building a reliable, repeatable experiment for the measurement of Tesla turbine efficiency by using an induction machine generator coupled to the shaft as a dynamometer. The power delivered to the generator, combined with fluid flow measurements at the turbine ports, are used to obtain turbine efficiency. Three optimal disk spacings are obtained by first relating output power and turbine efficiency to disk spacing by running the experiment with flat disks. The three best performing disk spacings are used to design the flat and curved disk turbine rotors for efficiency and output power comparison, where all other turbine geometrical parameters are kept the same.

 

The paper experimentally demonstrates the possibility of improving Tesla turbine output power by solely applying a curvature to its rotor disks. Experimental results show a 10-15% power output improvement over flat disks across the optimal turbine operating range of 17.5k RPM - 22.5k RPM.  

Presenting Author: Federico Coppo University of Wisconsin - Madison

Presenting Author Biography: Federico Coppo received his B.S. degree in mechanical engineering and electrical engineering from Boston University, Boston, MA, USA, and the M.S. degree in electrical engineering from the University of Wisconsin-Madison, Madison, WI, USA, in 2021 and 2023, respectively. From 2022 to 2023 he was a Research Assistant with the Wisconsin Electric Machines and Power Electronics Consortium (WEMPEC).

Authors:

Federico Coppo University of Wisconsin - Madison
Riccardo Bonazza University of Wisconsin - Madison
Daniel Ludois University of Wisconsin - Madison