Smith 



several problems of naval hydrodynamics, and other problems stemming from 

 Laplace's equation. 



A preliminary idea of the power and of the state of development of the 

 method of analysis will be conveyed by an example. Studies supported by NASA 

 (e.g., "Study and Development of Turbofan Nacelle Modifications to Minimize 

 Fan-Compressor Noise Radiation," Contract NASI- 7 130) are underway to re- 

 duce the noise of jet engines. Figure 1 illustrates one tjrpe of inlet that has 

 been designed. It was tested on the ground at full scale under full-power con- 

 ditions. The two ring airfoils have a double purpose; first, to block passage of 

 noise to the exterior from the fan blades, and second, to provide more area for 

 sound-absorbing material, because the vanes are constructed of such material. 

 The ring airfoils have outwardly directed lift to keep them in tension. As the 

 sketch shows, the inlet consists of four separate bodies; the outer cowl, the 

 two ring airfoils, and the centerbody. The problem further consists of mixed 

 internal and external flows. The vanes as well as the basic inlet were all 

 analyzed as a unit, so that mutual interferences would be properly accounted 

 for. The vanes were shaped and positioned so as to obtain minimum disturb- 

 ance to the flow by selecting a total configuration, calculating the flow, finding 

 bad pressure distribution features, and correcting them by changes in shape, 

 recalculation, etc., until all the pressures appeared to be the best that could 

 be expected. Boundary layer calculations went hand in hand with the potential 

 flow calculations. The design and analysis were performed by John Hoehne, 

 who is strictly a routine user of the computing program as a design tool, with- 

 out any need for assistance from those such as John Hess, who has done most 

 of the development. As a matter of fact, while the author was aware of the 

 NASA noise reduction project, he was quite unaware of this particular work 

 until told of the successful ground tests. These tests showed a large reduction 

 in sound level and a barely measurable loss in thrust. 



Fig. 1 - An experimental "quiet" turbojet in- 

 let designed by means of the present method 

 of potential -flow calculation. 



318 



