Comparisons of boundary-layer transition measurement techniques at supersonic Mach numbers

Abstract

Four different boundary-layer transition detection techniques—very thin hot films, liquid crystals, infrared imaging, and an optical interferometer—were compared using the same flat-plate model for the same tunnel conditions. The comparisons, conducted at the NASA Langley Research Center, involved not only their sensitivity to transition but also their ease of use. The thin films, as expected, gave excellent quantitative information and were used as the standard for evaluating the other techniques. Both the liquid crystals and infrared imaging were able to detect transition before the boundary-layer intermittency factor had reached 50%. The optical interferometer was unsuccessful. Conditions sampled included a range of Mach numbers from 1.5 to 2.5 and unit Reynolds numbers from 3.3 to 13.1 x 10 6/m.