which the required equipment was being built it was decided to develop a qual- 

 itative technique for outlining the regions of laminar, transitional, and 

 turbulent flow on a ship model. 



It is well known that laminar flow gives rise to smaller shearing 

 stresses than turbulent flow at the same Reynolds number, and hence, that a 

 resistance test of a model With a laminar layer over a portion of the wetted 

 surface gives drag measurements from which the power predictions for the pro- 

 totype may be seriously underestimated. It is also well known from wind- 

 tunnel investigations and from theoretical studies on bodies of aerodynamic 

 interest that the extent of the laminar region depends strongly upon the pres- 

 sure distribution and hence the shape of the forebody. Consequently, mislead- 

 ing results might possibly be obtained from drag tests of several models repre- 

 senting, say, competitive bow lines for a ship or a geometric series of lines 

 of varying forebody fullness because of the unequal laminar effects on each 

 model . 



Ship-model experimenters have long realized that such conditions 

 prevail for small models and employ various devices to stimulate the boundary 

 layer to secure a turbulent layer over the entire model. Evaluation of the 

 effectiveness of the stimulators is made only by interpretation of the char- 

 acter of the resistance curve. Pew attempts have hitherto been made to in- 

 vestigate the boundary-layer flow itself to ascertain the effectiveness of the 

 stimulator in producing turbulent flow over the entire wetted surface. Large 

 ship models (16 to 30 ft) have been used for years at the larger model basins 

 to avoid the difficulties of laminar flow encountered with small models. 

 Those experimenting with large models have believed that the model size and 

 hence the Reynolds numbers were great enough to make negligible the effects of 

 any possible laminar flow. However, recent studies have revealed that full- 

 form models, even as long as 25 ft, have considerable laminar flow and that 

 the resulting error may range from 2 to 10 percent of the power required by 

 the ship even at designed speed. 



The immediate problem of this project was to devise some method of 

 detecting the extent of the laminar, transitional and turbulent flow over the 

 surface of the model. Having accomplished this it would then be possible to 

 assess the value of various devices which may be used to induce artificially 

 a turbulent boundary layer over the entire model . Several schemes were pro- 

 posed including chemical and photographic techniques but the hot-wire method 

 seemed to hold the most promise and has accordingly been pursued. This method, 

 which will be described, has been used to survey the boundary-layer flow on a 

 tanker model under various conditions of turbulence stimulation. The results 



