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The mechanical and performance test evaluation of an experimental high pressure ratio single-stage centrifugal compressor incorporating a rotating vaneless-vaned diffuser is discussed. The test rig employed was a turbodrive configuration with the centrifugal impeller driven by a directly-coupled air turbine. The rotating diffuser was supported on a separate shaft operating at approximately 25% impeller speed and directly coupled to a high-speed water brake. Mechanical operation of the compressor rig was satisfactory. Best overall test performance achieved at design speed was a total-total pressure ratio of 7.7 with an adiabatic efficiency of 72.3% (average stage exit Mach number of 0.27). A broad flow range ratio of 1.25 between choke and surge was obtained with the diffuser rotating at design speed.

The performance development history of a small gas turbine for the U. S. Army 10 kW turboalternator is discussed. The design incorporates a single-stage centrifugal compressor and single-stage radial inflow turbine, mounted back-to-back on a common shaft rotating at 93,500 rpm and directly coupled to a variable frequency solid alternator. Total accumulated running time, at rated speed during development, exceeded 20,000 h; in addition, a 2000 start/stop test was successfully completed. Gas turbine performance was found to be quite sensitive to compressor and turbine clearances as a consequence of the small compressor and turbine blade heights. With accurate control of these clearances, it was possible to attain average engine specific fuel consumptions meeting contract requirements of 1.1 lb/hp·h with a low rated turbine inlet temperature of 1330°F.

Results are presented of a study directed toward providing a method of estimating radial turbine efficiency levels and performance characteristics, based upon summation of the individual component losses and applicable energy relationships. The magnitudes and divisions of the component losses have been developed to closely coincide with actual turbine test data obtained at the author's company, and have been integrated into a method of obtaining the complete turbine characteristic once the turbine geometry and operating conditions are prescribed. Because of the lack of radial cascade data, the use of a so-called one-dimensionalflow theory is employed, supported by theoretical cascade analysis and adjusted by empirical means to satisfy the strong three-dimensional flow conditions that can exist in a radial turbine, particularly at off-design conditions.