Tesla bladeless turbomachines are recently being investigated due to many advantages such as its simple design and ease of manufacturing. It consists of flat, thin, smooth disks mounted parallelly on the shaft with spacers between them to maintain constant gap. Fluid enters tangentially through stator and leaves the rotor axially while imparting torque on the disk. In the past, low efficiency of the Tesla expander is recorded citing main losses occurring in the stator and viscous friction at the end disks due to ventilation. If an efficient design is achieved, this will be a promising machine in the area of small-scale power generation and energy harvesting. This paper focuses on experimental performance investigation of 3 kW (rated electrical power) Tesla bladeless expander along with vibration-acoustic test of the rotor. The Tesla expander and the electric generator are housed in a single casing making it first of its kind being tested with such configuration. The expander is fed with air and operated at high rotational speeds up to 40000 rpm. The expander has two exhausts of which one exhaust passes over generator for cooling purpose. The test is carried out with different number of nozzles to understand its effect on the performance. The real time performance of expander and generator is recorded.

Performance results show that the peak efficiency for two nozzles is better than one nozzle for the same inlet pressure conditions.  Furthermore, one of the most important losses in Tesla turbomachines, ventilation loss, is experimentally evaluated. Ventilation losses, for the first time, are extensively discussed based on experiments.  The ventilation losses together with bearing loss are characterized using experiment data and numerical analysis.

Regarding roto-dynamical features, Tesla turbine rotor assembly is composed of several thin disks which leads to some peculiar vibrational criticalities. Thus, specific vibro-acoustic tests were carried on obtaining a complete machine dynamical characterisation. Data is acquired during machine run up, run down and with some speed regimes. This test was conducted feeding different numbers of turbine nozzles with and without the load due to the generator. Collected data analysis allows to identify, for each turbine speed, the frequency contents in the vibration signals and to associate them with their possible sources. Moreover, vibrational analysis permits the identification of machine critical speeds, rotor and stator resonances. Vibrational measurement provides a base line level related to the machine safety condition which will be used for operational monitoring. The combined analysis of performance and vibro-acoustic tests enables the design of efficient and dynamically stable Tesla expanders.


Experimental Investigation on a 3 kW Air Tesla Expander With High Speed Generator

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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