flow speeds ranging from 94 to 133 cm/sec. The streamer trap nozzle with a 

 hydraulic efficiency closest to optimum (F^ — 0.94) was the C nozzle. Both 

 the DUCK85 and SUPERDUCK nozzles had hydraulic efficiencies near optimum over 

 the full range of flow conditions (E h = 0.88 and 0.90, respectively). 

 Flow visualization tests 



48. String and dye were used as qualitative indicators of flow patterns 

 around selected nozzle types. Several pieces of string approximately 30 cm in 

 length were tied to two steel reinforcement bars which were placed upright in 

 front of nozzles, as indicated in Figures 17a and b. The string became 

 aligned with the flow, giving qualitative indications of flow patterns in the 

 vicinity of the nozzle. The only nozzle with a noticeable effect on the 

 string patterns was the H-S trap, which tended to suck the string into the 

 nozzle. Dye released from a plastic tube immersed in the flow gave similar 

 qualitative information about flow characteristics in the vicinity of the 

 nozzle, with the H-S trap exhibiting a similar suction effect. 



Summary of Hydraulic Test Results 



49. From the hydraulic tests, four nozzles were identified for further 

 analysis: the SUPERDUCK and C nozzles, because of their near-optimum 

 hydraulic efficiencies; the DUCK85 nozzle, because it had been used in the 

 DUCK85 field project, is easy to manufacture, and proved to have a 

 hydraulic efficiency close to unity; and the H-S nozzle for comparison. 



50. Figures 18 and 19 present the uniform flow (midflow) and bottom 

 flow hydraulic efficiencies and standard deviations for the four nozzl.es at 

 the four flow conditions (V mid equal to 22, 43, 59, and 74 cm/sec). Values of 

 hydraulic efficiency at each measurement point (Figure 16) in the nozzle were 

 used to calculate the standard deviation. The hydraulic efficiency at each 

 point in the nozzle was calculated by dividing the flow speed at a point with 

 the trap in place by the ambient flow speed at that same point. Lengths of 

 vertical lines at each point represent one standard deviation about the mean. 

 Standard deviations therefore give an indication of the spatial variability of 

 flow speed at the nozzle. Figure 20 presents the variation in hydraulic 

 efficiency with flow speed for the two-streamer (2ST) tests. The SUPERDUCK 



37 



