A,27 • PRESENT STATUS AND FUTURE DIRECTION 



the model temperature remains nearly equal to the free-air temperature 

 and thus the conditions are those of a cool body to which heat is trans- 

 ferred from the boundary layer. The models were long cylinders with 

 tangent-ogival nose, the over-all fineness ratio being 30. They were sta- 

 bihzed by cruciform fins. Under the test conditions the critical Reynolds 

 number for the smooth body at 0° angle of attack or on the windward side 

 was greater than 11|- million. 



Van Driest and Boison [ISO] report that cooling a 20° cone in the 

 North American Aviation S^-inch wind tunnel to (Tw — T,)/T°^ of -0.38 

 increased the transition Reynolds number from about 2.7 million to a 

 value greater than 5.4 milhon, the maximum permitted by the length 

 of the cone. 



Jack and Diaconis [121] made measurements on a cone-cylinder and a 

 paraboloid-cylinder at a Mach number of 3.12 in the NACA Lewis 1-foot 

 variable pressure wind tunnel. Heating the cone-cyhnder to {T„ — T^)/Tl 

 equal to 0.53 decreased the transition Reynolds number from 2 million 

 to 0.86 milhon; coohng to —0.45 increased it to 10.6 milhon. For the 

 paraboloid-cyhnder the transition Reynolds numbers were approximately 

 twice as great. 



Snodgrass [122] reports the results obtained on a 10° nose cone on a 

 Viking rocket in free flight. The individual observations of transition are 

 plotted in Fig. A,26c. They are in fair agreement with the Dunn and Lin 

 curve. 



Bertram [109] reports an exploratory investigation of transition on a 

 hollow cyhnder in the NACA Langley hypersonic blowdown wind tunnel 

 at a Mach number of 6.9. Because of the short duration of flow the body 

 did not reach the recovery temperature. The value of (Tw — T^)/T^ is 

 estimated to have been —0.27 and the observed transition Reynolds 

 number was between 4 and 6 million. 



The results described in this section include results in wind tunnels 

 in which Ret for the body without heat transfer varies from L3 to 11.5 

 million, these differences presumably being due principally to effects of 

 air stream turbulence. While the absolute changes in Re^ with heat trans- 

 fer are greatest in those wind tunnels where the highest values are ob- 

 served for the insulated body, the relative changes for small rates of heat 

 transfer are of the same order of magnitude. As the cooling is increased, 

 the curves of Ret vs. (Tw — T^/Tl indicate vertical asymptotes corre- 

 sponding to values of (Tw — T,)/Tl which are in fair agreement with the 

 values for complete stabilization computed by Dunn and Lin. 



A,27. Present Status and Future Direction. It has been seen 

 that transition is a phenomenon of wide occurrence in many types of flow 

 and that its location in the flow is governed by a large number of varia- 

 bles. The problem of transition is the problem of the origin of turbulence 



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