The Bladeless Propeller 



this agreement should not be interpreted as an indication that the upper limit of 

 performance has already been attained. Indeed, the theoretical prediction, being 

 based on an analysis that does not account for the finite thickness of the primary 

 jets, is likely to be pessimistic except for very small area ratios. 



Measurements made at McDonnell Aircraft (Ref. 9) have shown that rotary 

 jet mixing can be accomplished within rather short mixing duct lengths. This 

 observation appears to be confirmed by the results of an experimental program 

 recently reported by Palcza (Ref. 17). Less is known about the extent to which 

 mixing progresses during the deflection phase. Comparison of theoretical and 

 experimental results in Figs. 12 and 14 seems to indicate that the actual en- 

 trainment coefficient may exceed the estimated value. 



Air-to-air models with large coning angles have been extensively tested by 

 Avellone (Ref. 18). These models had an externally -driven, thin-walled rotor 

 with sharp-edged orifices, incapable of imparting a significant tangential mo- 

 mentum to the primary fluid. Thus, the spin angle could be varied continuously 

 by just varying the rotor speed. Typical results of these tests are shown in Fig. 

 13, where they can be compared with the theoretical predictions of Ref. 10. 



Two-phase underwater propulsion tests have recently been reported by 

 Avellone and Sarro (Ref. 19). The model used was of the axial-flow type and 

 had an externally-driven, thin-walled rotor for continuous spin angle control in 

 the same manner as the Avellone air-to-air model. In all tests the optimum 

 spin angle was found to be between 1° and 2°. Some of the reported test points 

 are plotted in Figs. 15 and 16. Direct comparison of the experimental results 

 with those of the available theories for two-phase interactions is not yet possi- 

 ble in this case, because the primary fluid used in these tests was steam, 

 whereas numerical results of the theories are available only for the case of a 

 noncondensing primary. It will also be noted that, whereas the theory (Ref. 14) 

 predicts a decrease of thrust augmentation with increasing pressure ratio, the 

 experimental results are still inconclusive in this respect. Clearly, there is a 

 great need for further research in this area, particularly since it is evident 

 from Figs. 15 and 16 that the possibility still exists for vast improvements in 

 the performance of two-phase bladeless propellers. 



CONCLUSIONS 



1. The bladeless propeller has the distinct advantages of efficiency and 

 compactness over the conventional steady-flow ejector, and the distinct advan- 

 tages of simplicity, ruggedness, and flexibility of operation over existing 

 nonsteady-flow thrust augmenters. 



2. The superiority of the bladeless propeller over the ejector increases as 

 the secondary -to -primary density ratio is increased, all other conditions being 

 equal. 



3. For each spin angle there exists a secondary-to-primary area ratio that 

 produces the maximum augmentation; and, similarly, there exists for each area 

 ratio an optimum spin angle. These optima depend on the density ratio, the 



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