UNUSUAL BOUNDARY-LAYER TRANSITION RESULTS ON CONES IN HYPERSONIC FLOW

Nonablating, 5° and 15° half-angle cones were tested as part of a program to study the effects of subliming ablation on boundary -layer transition. Test results indicated transition Reynolds numbers to be 1) independent of local unit Reynolds numbers, 2) equal to those usually observed or higher, and 3) decreasing as the boundary-layer edge Mach number increased from 5 to 6.8. The first two of these unusual results may be due to a unique feature of the wind tunnel: a low-molecular-weight, helium-air boundary layer. Additional data show an effect of tunnel boundary -layer molecular weight on transition. Also, a new transition correlation for cones shows the aforementioned transition dependence on edge Mach number to extend to Mach numbers from 3 to 8. Tests were conducted at nominally constant freestream Mach number (7.4), wall- to- total- temperature ratio (0.4), and total temperature (1500°R). Total pressure ranged from 200 to 1800 psia; accordingly, freestream unit Reynolds numbers varied from 0.9 to 8.0 × 106/ft. Transition was defined from heat-transfer measurements. Preliminary results from 5° cones indicate no significant effect of camphor ablation on transition at an edge Mach number of 6.8. © 1969 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.