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operation and was also cut back for increased area operation. These modifications were employed to vary stator throat area frcun 20 to 144 percent of the design throat area and rotor throat area from53 to 137 percent. Figure 14 shows the rotor as designed, with the reducing extension, and cut back. Details on the geometry, test results, and interne3 velocity calculations are described in Ref. 7. Performance was then experimentally determined for thirteen combinations of stator area and rotor area. Figure 15 shows the envelopes of the design- speed efficiency curves obtained with each rotor configuration. Specific speed for each stator-rotor combination was varied simply by varying overell pressure ratio at design speed. Note that total efficiencies over 0.90 were measured for specific speeds between 0.37 and 0.80. At the high and low ends of the high efficiency range of specific speed, the ratio of stator throat area to rotor throat area was near the design ratio. Efficiency vias lower for area ratios not near the design ratio. The best combination in terms of de- sign area were 42-53 (stator-rotor) percent and 144- 137 percent. These provided just about design stator reaction. Velocities in the flow passages upstream of the throats, however, deviated considerably fram the design internal velocities because of the dif- ferent volume flows. The high volume flow was more than four times the low volume flow. Blade surface velocities for each stator-rotor canbination were calculated and included in the reference. The low flow case solution, Fig. 16, indicated a large pres- sure surface flow eddy extendingfrautheleading edge halfway through the splitter blades on the shroud and well beyond the splitter blades along the hub. Also, velocities near the inlet are quite low. An examination of internal losses, based on flow measurements showed that rotor losses increased by about 0.006 in total efficiency in reducing the flow areas from design values tothe42 to 53 percent combination. OveraJl efficiency decreased frau0.930 to 0.895 with the loss increase ocdurring largely in the stator. Figure 17 shows the internal flow velocities calculated for the high flow (144-137 percent) case. The velocity levels upstream of the throat are con- siderably higher than i n the low flow case, indi- cating higher blade loading, lower reaction, and all velocities w e l l above zero, i.e. no flow eddy. Total efficiency was 0.92, indicating very slight in- creases in stator and rotor viscous losses Over those of the design area configuration. This investigation indicated again that radial turbines are relatively insensitive to unfavorable flow conditions in the upstream part of the rotor passages. CONCLUDIliG FQWVXS The radial turbine effort began at the Lewis Research Center as technical support for the Brayton cycle space power program. The intent was t o learn more about the performance characteristics in order to increase efficiency and to properly assess losses where comprdses might result frm mechanical and thermal considerations or any other operational re- quirements. The analytical techniques in flow analy- sis, off design performance estimation, etc., and ex- perimental information have been helpful in system studies and advanced component designs. : splitters, and tandem rotor blades. A second effort is the study of the effect of rotor tip cutback on radial turbine performance. 3 The radial turbine program is continuing in sup- port of both the Brayton cycle space power program and advanced small airbreathing engine programs in- volving such applications as helicopter, AN, vehic- ular, etc. One effort in process involves an ad- vanced turbine suitable for the 2-10 kW single-shaft system. The design employed lonowledge obtained in the radial turbine studies a8 well as some axial turbine investigations. The turbine has stators with converging endwalls for low-velocity turning, no Other studies under way are directed a t problems associated with high temperature cooled radial tur- bines. One such design is currently under way that includes a low blade number, no splitters, and very thick leading edges at reduced diameter to accommo- date cooling and resist erosion damage. Another area of effort is that of radial turbine erosion and m?th- ods for its reduction. These programs are directed at achieving the reliability and structural integ- r i t y required f a these small turbines while main- taining the high efficiency levels associated with more ccmventional radial turbines. REFERENCES 1. Rohlik, H. E., Kofskey, M. G., and Katsanis, T., ''Sunrmary of NASA Radial Turbine Research Related to Brayton Cycle Space Pbwer Systems," TM X-52298, 1967, NASA, Cleveland, Ohio. : Small Size, Low Power Gas Turbines," TM X-52522, NASA, 2. Futral, 6. M., Kofskey, M. G., and Rohlik, H. E., "Instrumentation Used to Define Performance of Cleveland, Ohio. 3. F'utral, S. M. Jr., and Holeski, D. E., "Ex- perimental Results of Varying the Blade-Shroud Clearance i n a 6.02-Inch R a d i a l Inflow Turbine," TN D-5513, 1970, NASA, Cleveland, Ohio. 4. Futrd, S. M. Jr., and Wasserbauer, C. A., "Experimental Performance Evaluation of a 4.59-Inch Radial-Inflow Turbine With and Without Splitter Elades," TN D-7015, 1970, NASA, Cleveland, Chio. 5. Nusbaum, W. J., and Kofskey, M. G., "Radial- Inflow Turbine Brformance with Exit Diffusers De- signed for Linear Static Pressure Variation," TMX- 2357, 1971, NASA, Cleveland, Ohio. 6. Nusbaum, 8 . J . , and Kofskey, M. G., "Cold Performance Evaluation of a 4.97-Inch Radial-Inflow Turbine Designed for a Single-Shaft Brayton Cycle Space-Paver System," TN D-5090, NASA, Cleveland, Ohio, 7. Kofskey, M. G., and Nusbaum, W. J., "Effects of Specific Speed on the Experimental Performance of a Radial-Inflow Turbine," Proposed Technical Note.PDF Image | RECENT RADIAL TURBINE RESEARCH AT NASA Lewis
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