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.I turbines. The turbines had different design point clearances as s h m , and different sensitivity t o blade-shroud clearance. It should be noted that in a U cases s h m the clearance was increased from the design value by rempving blade material. The slopes of the curves show that the radial-inflow turbine was least sensitive to clearance change. One percent of passage height removed from the blade resulted i n 1.3 percent loss in specific work output. Corre- sponding values for the impulse and reaction axial turbines were 1.8 and 3.0. Figure 5 show the separated effectsofinlet clearance and exit clearance on efficiency. The exit, clearance is the more influential by a factor of ten in the 0 to 8 percent clearance range. Clearance near the trailing edge is obviously the controlling influence, determining that fraction of the flowthat is fully turned to the exit blade w e . Since the turbine stator sets up the available whirl, this means that the design specific work is very nearly achieved even with relatively large inlet clearances. The efficiency s h m a slight drop because of the losses incurred in the clearance space. This would probably be true in the case of an axial turbine with extremely hi& solidity. This light loading and favorable reaction providh an appreciable margin for the kind of flow modifications resulting fram the splitter removal. The splitter investigation was reported i n Ref. 4. EXIT DIFFUSER INVESTIGATIONS Three diffueers were designed for the turbines of 8 2-10H space pawer system.(5) me first of these had a cylindrical inner body and a conical outer wall sized for the recovery of 60 percent of the rotor exit velocity he&l. Figure 10 shows the efficiencies, totalandstatic, ofthe turbinewith and without the diffuser. The diffbser loss was con- siderably higher than anticipated. The diffuser loss accounts for 0.02 in total efficiency at design Rey- nolds number. The s t a t i c pressure recovery provided a static efficiency gain of 0.015. Conical dif- fusers have the maxjnnnn rates of change of s t a t i c pressure and velocity a t the inlet. This should provide minimum loss and m i n i m u likelihoodof sepa- ration because the boundary layer is thinnest and the Reynolds number highest. The effect of blade wakes and rotor passage gradients, however, &e not taken into account in the boundary layer analyses used, and could r p e c t the separation characteris- ticsoftheb0uiku-ylayer. Consequently, asecond diffuser was designed to allow some mixing upstream of the most rapid change in velocity. Static pres- surewas scheduled to vary linearly from inlet to J 2 discusses these effects in sane detailandalso in- cludes the results of radial surveys of flaw angle, total pressure, and total temperature at the turbine exit for each clearance configuration. SKITTER BLAE RFmvfi The effectofblade loading near the rotor inlet wasexaminedexperhntdlyinanU.7mscalemodel of the turbine used in the clearance investigation. The splitter blades were removed, doubling the blade loading in the upstreamhalfofthe rotor; Fig. 7. Channel velocities were then calc-ted for both cases, with and Without splitters. The results are shown in Fig. 8. The negative velocities on the pressure side of the blade indicate a flow eddy ex- tending fromthe hub almost to the meridional 50 per- cent streamline. The large increase in loading up- stream of the splitter trailing edge location i s also s h m . Turbine performance data were taken over a range of speed and pressure ratio, showing very little dif- ference between the splitter and the no-splitter cases. Figure 9 shows the variation in efficiency with blade-jet-speed ratio at design speed. Note that the efficiency with no splitters was slightly higher than with the fully bladed rotor at design point operation. The loss increase due to the load- ing increase was apparently offset by the reduced surface area. This result and the results of the clearance investigation indicate an insensitivity to poor flow conditions near the leading edge as indi- cated by the channel velocity calculation. An esti- mate of solidity based on average blade spacing pro- vides some insight into this. After removal of the splitters the average ratio of chord to spacing was about 2.6, approximately double the solidity required for an axial turbine with comparable turning. Also, the inlet kinetic energy is very low, and the rotor reaction, defined as the ratio of relative kinetic energy increase to turbine specific work, is 0.2. corresponding velocity scheduleisaleo shown in Fig. ll(b). The resulting wall contour, with a tapered innerbody, is the trumpet-lih shape in fig. 12. A t h M diffuser was very similar t o the second, but with a cylindrical body. Figure U shows the overall t o t a l efficiency and static efficiencyofthe turbine with each diffuser. Thegainwiththe diffusersdesignedforalinear variation in static pressure was about 0.01 intotal efficiency. The diffbser losswas cut in half. Measurementaccuracywas criticalhere, withthegain i n efficiencies Shawn resulting from small differ- ences in measured pressures at the design Reynolds number operating point. The measurements were con- firned therefore at a higher level, 13.8 N/m2 inlet campared to 4.8 N/& inlet, in order to increase the certainty of the conclusions. SPECIFIC SPEED INVESTIGATIONS The development of high-speed turbomachinery i s expensive. It is therefore desirable to use a given basic design for a varietyofapplications with dif- ferent power levels. The closed loop space power program includes a raage of power levels with the common requirement ofhigh efficiency. The desired operating range could be achieved without major change in the turbine and compressor by three methods. Operating pressure could be changed with ncmindy constant pressure ratios. This would change mass flowbut not volume flow. Metering areas could be changed by s h p l y changing blade angles. This could change volume flow and mass flow. Or sane combin- ation of these could be employed. The flow area approach has advantages in system size and system duct and heat exchanger pressure drops. The 12.6 cm turbine mentioned previously(6) was modified to accept a series of stator blade.mws with different numbers of blades and blade W e s . The rotor was fitted with an extension for reduced area The effects of inlet and exit clearance on mas6 flaw are s h m in Fig. 6. Here again the exit clear- ance i s most influential, since the exit flow area is the effective orifice in the rot&. Reference3 exitofthe diff'user as shown in Flg. ll(a). 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