Measurements of Transition-Front Asymmetries on Ablating Graphite Nosetips in Hypersonic Flight

Transition experiments were conducted on preablated graphite nosetips in the AEDC Track G facility. Nosetip radius and freestream static pressure were varied to insure transition front movement from sonic-line to stagnation-point proximity. Surface temperature contours were measured with image-converter cameras and results interpreted with interactive graphics to define instantaneous transition front contours. Statistical analyses showed that probability of transition occurrence on any given ray, between the minimum and maximum observed run lengths to transition, was Gaussian. Mean transition front location was observed to progress forward with a power-law dependence on range static pressure; coincidently, transition-front asymmetry, defined by a standard deviation about the mean, was noted to decrease linearly. All results were found to be independent of nosetip radius.