Favre and Coantic 



SMOOTH 

 JOINING 



CONTRACTION 



WATER INLET 



Fig. 8. Details of junction between air and water flows, and arrang£- 

 ment of the submerged wavemaker. 



5. Further Details and Conclusions 



At each step in the design of the facility, we endeavored to 

 improve the simulation of the natural phenomenon and some of the 

 arrangements taken to this end have just been described. A peculiar 

 problem was set by the parasitic boundary layers which unavoidably 

 originate along the side walls and ceiling of an elongated working 

 section, and which are known to result in cumbersome secondary 

 motions. The dispositions adopted to reduce these effects, thereby 

 improving the representation of the unlimited atmospheric-oceanic 

 system, are represented by Fig. 9. The cross sectional shape of 

 the working section (see Fig. 9(a)) has been designed with a height/ 

 width ratio of 1 to 2.2, and furthermore fitted, like in the Water- 

 loopkundig Laboratorium [1966a, b] design, with vertical plates 

 restricting the span of the useful water surface to 2. 62 meters. 

 The lateral quays thus realized will limit the parasitic dynamical as 

 well as thermodynamical effects in the central part of the working 

 section, where the measurements will be performed. To further 

 improve the two-dimensionality of the flow, and to prevent the inter- 

 action of the studied boundary layer with that one developing on the 

 working section's ceiling, boundary layer control devices will be 

 used. As shown by Fig. 9 (b) , they combine boundary layer suction 

 (by means of slots or porous walls) and blowing (through slots), 

 taking advantage of the possibilities of tangential blowers. 



At last, it will be necessary, specially at the lowest wind 

 velocities, to artificially trigger transition, and eventually to in- 

 crease the boundary layer thickness, by means of devices similar to 

 those studied by Counihan [ 1969] or Campbell and Staden [ 1969] . 



50 



