Boundary-Layer Transition Experiments on Pre-ablated Graphite Nosetips in a Hyperballistics Range

An experimental program was conducted to test the validity of extrapolating the PANT (Passive Nosetip Technology) boundary-layer transition correlation, based on wind-tunnel/calorimeter-model results, to actual nosetip materials exposed to actual reentry environments. Pre-ablated ATJ-S graphite nosetips were flown on specific ballistics range trajectories through both air and nitrogen (with and without ablation). Surface temperature contours were measured via electrooptical pyrometry, from which transition zone presence and location were inferred. Significant discrepancies were noted between predicted and experimentally observed transition zone behavior, as influenced by Reynolds number and wall-temperature effects. A question was raised concerning characterization of a surface microroughness distribution, for transition purpose, by its median value. In addition, significant surface roughness effects on laminar-flow heat-transfer rates were noted.