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Experimental Investigation of the TurboClaw® Low Specific Speed Turbocompressor

[+] Author Affiliations
K. R. Pullen

City University, London, UK

S. Etemad, R. Cattell

Dynamic Boosting Systems, Kingston upon Thames, Surrey, UK

Paper No. GT2012-69074, pp. 735-742; 8 pages
doi:10.1115/GT2012-69074
From:
  • ASME Turbo Expo 2012: Turbine Technical Conference and Exposition
  • Volume 5: Manufacturing Materials and Metallurgy; Marine; Microturbines and Small Turbomachinery; Supercritical CO2 Power Cycles
  • Copenhagen, Denmark, June 11–15, 2012
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-4471-7
  • Copyright © 2012 by ASME

abstract

For both radial and axial turbocompressors there are well established design methods which direct the designer to the optimum shaft speed for a given flow rate and pressure rise. This shaft speed is relatively narrow in range if the highest efficiency is to be obtained. However, there are many reasons why shaft speed is dictated by other considerations and it is more common to find that the turbocompressor must operate far below the preferred shaft speed. The present contribution describes numerous applications where this occurs, the majority of which are when volume flow rates are relatively low.

Many researchers have attempted to find solutions to this problem and the starting point is to take a radial compressor and design it for operation at lower than optimal speed. This creates high windage and tip leakage losses relative to the useful work component which becomes punitive as the exit blade width is reduced. In addition to this, for small machines, the size of the exit blade width itself becomes an issue as it reduces to less than around 3mm leading to high relative tip clearances and narrow passages.

The purpose of this paper is to describe a novel solution that has been developed which is based on a combination of a partial entry rotor and extremely high forward sweep, a new class of machine denoted TurboClaw®. The level of forward sweep is substantial, at almost 90° that it is beyond the experience of fully bladed machines with levels of forward sweep below 30°. The machine is stable with extremely high tangential to radial Mach number ratios well over 20 being achieved. Experimentally produced maps for various sizes of machine are presented which demonstrate that the characteristic is very similar to that of an equivalent radial machine which would have to operate at speeds between two to four times greater.

Further experimental work is described which has taken place on both small prototype machines and on a larger version using a specially designed test rig capable of producing accurate performance measurements based on shaft torque. The test rig has been designed to allow flow visualization and non intrusive flow measurements. A selection of results from these tests is also described. At the levels of performance reached to date this class of machine is already suitable for a number of commercial applications including fuel cell air management systems, electric supercharging, and other industrial applications. Results of research and development programs in these areas are also described.

Copyright © 2012 by ASME

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