by the flow around it. An insulation (a vinyl plastic coating: Chem- 

 Sol Plastisol material) is applied to the portion of the wire holder which 

 is submerged. The platinum wire is soldered to the horizontal rods that 

 are visible at the top and bottom of the figure . These two horizontal rods 

 are welded to a vertical strut barely visible (and out of the plane of focus) 

 in the right background of the photograph. This vertical strut is positioned 

 so that it is not in the plane of the bubbles (the plane of focus) and^ con- 

 sequently^ does not interfere with the bubble patterns near the platinum 

 wire except near the soldered ends . The region behind the platinum wire 

 affected by the horizontal wire supports is easily observed^ and the wire 

 is always positioned to utilize the center portion of the bubble patterns 

 for flow analysis. Figure 2 shows four platinum wire holders. 



The distance between the bubble rows behind the wire depends on the 



2 k 

 velocity at the wire and the period of the pulsed voltage . ■* The velocity 



at the wire is directly proportional to the bubble-row separation and 

 inversely proportional to pulse period^ the constant of proportionality is 

 the scale factor encountered in the photograph (see analysis below). For 

 the 0.001- in. wire shown in Figure 1, the diametral Reynolds number is 

 below kO for velocities in water up to 5 ft/sec. Consequently, there is 

 no vortex shedding behind the wire itself as shown on page I'J of Reference 5° 

 The velocity recovery is assumed to occur within a very short distance 

 downstream of the 0.001~in. diameter wire. By this means, a close approxi- 

 mation of the local longitudinal velocity profile is achieved. Note that 

 the determination of such a longitudinal velocity profile is achieved by 

 these means only when the stretching or compressing of the bubble rows along 

 their length is minute compared to their horizontal translations (see below). 



For a Reynolds number, based upon the cylinder diameter, less than kO, 

 the two vortices remain attached to the cylinder independent of the time 

 variable. That is^ there is no oscillatory feat'ore in the wake, and 

 disturbances downstream of the cylinder appear to be rapidly damped out 

 near the cylinder. In the range of R between kO and I50, the flow 

 is termed "stable," The flow behind the cylinder is characterized by 



