Savitsky 



the wave probe. Thus, the transverse probes covered an area from 

 the grid centerline to a distance of nearly 9 ft outboard of the edge 

 of the grid. 



Test Procedure : The range of wave heights and lengths were 

 essentially similar to those used in the one -dimensional tests. Also, 

 the test procedures previously described were followed. The initial 

 grid location was always 10 ft ahead of the wavemaker. After ap- 

 proximately 60 ft of tow, the grid was stopped and the wavemaker 

 continued in operation until the wave amplitudes recorded in the line 

 of transverse wave probes were again equal to the incident wave 

 amplitude. 



RESULTS OF EXPERIMENTAL INVESTIGATIONS 



Selected test results are first described to illustrate the 

 general behavior of waves in a turbulent flow field. An elementary 

 analysis of the results is developed in the subsequent section. 



One-Dinaensional Grid Studies 



As previously discussed, the original intention of the one- 

 dimensional grid study was to provide a turbulent wake with constant 

 longitudinal mean flow in any transverse section through the wake. 

 Regular waves would be passed through the wake and measurements 

 made of the dissipative effects of grid-controlled turbulence on wave 

 amplitude attenuation. It was expected that the deep water gravity 

 waves would pass through the turbulence field with the crest lines 

 always remaining parallel to the grid and that the wave amplitude 

 would be essentially constant cilong a given crest line and decrease 

 as the wave progressed further into the turbulent area. Under these 

 circumstances, the amplitude attenuation would be due both to 

 viscous dissipation and to "wave stretching" as it nnoved into a longi- 

 tudinal current from an originally quiet area. 



This idceilized situation did not develop but, rather, it was 

 found that the wave crest lines were severely deformed; the wave 

 amplitude was not constant across a given crest line; and, further, 

 there were pronounced oscillations in the wave amplitude time history 

 at each wave probe (whether moving or stationary) in the wake. In 

 all cases, the control wave probe, which was fixed in quiet water aft 

 of the turbulent wake. Indicated a wave of constant amplitude and 

 period continuously passing into the wake area. 



General Behavior: An example of typical wave amplitude 

 oscillations recorded by both the moving and stationary wave wires 

 along the grid centerline is given in Fig. 5. The test conditions 

 represented are for a wave length of 4.0 ft and a wave height of 

 1.2 inches. The grid velocity was 1.7 ft/sec. The phase speed of 

 the wave is 5.4 ft/sec while the average wake velocity is approxi- 



400 



