shedding causes rapid diffusion of the otherwise distinct edges of the 

 bubble rows. Further problems^ which time limitations in the present 

 investigation did not permit studying, related to the possibility of 

 excessire, but undetectable, wire oscillation and the deceptive velocity 

 fields behind these thin wires » It is obvious that such a body in a flow 

 has its own wake and this may obscure the wake profile that is being 

 investigated behind a foil or other shape , However, as seen in the photo- 

 graph, the delicate hardware can be arranged to install hydrogen bubbles in 

 flows having velocities far beyond speeds of 1 ft/sec. It is logical to 

 expect, therefore, that small, more delicate wires may be similarly 

 installed in flows where velocities reach 10 to 15 ft/sec without intro- 

 ducing the shedding errors that undoubtedly exist behind an 0.001- in. 

 diameter wire in flow velocities of 10 to 15 ft/sec (R > ko) . 



The following cathode-wire configuration has been found convenient in 

 determining the general characteristics of the three dimensionality of a 

 supposedly "two-dimensioTial" flow . The wire should be installed in the 

 flow in such a way that it is parallel to the generatrix of the body 

 about which the flow is being studied. For instance, if the wire is 

 positioned parallel to the trailing edge of the foil shape and perpendi- 

 cular to the flow direction, the "plan view" of the velocity field can 

 be observed o In fact, this was done by Hama and Mutant and the wire was 

 energized by a pulsed excitation. Figure 17 illustrates such a wire con- 

 figuration. The excitation of the wire near the trailing edge is with dc 

 voltage o The upstream kinked wire is energized similarly. In this 

 case, the trailing-edge wire is crudely attached to the straight walls of 

 the test section by means of tape . It should be mentioned that photography 

 parallel to the resulting wake bubble patterns produces blurred and 

 apparently poorly focused photographs . This is especially true for the 

 short depth of focus encountered with the necessary shutter openings . As 

 was done in Reference 3> photography should be performed perpendicular to 

 such bubble patterns^ unfortunately, time did not permit the alterations 



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