Photogrammetric Measurement of Recession Rates of Low Temperature Ablators Subjected to High Speed Flow

This research advances a technique to simulate high temperature/high speed effects in a high speed/low temperature environment and to capture recession of the test article in three-dimensions. A method of fabricating dry ice test articles was developed, and the AFIT Mach 3 pressure-vacuum wind tunnel was used in combination with the dry ice test articles to collect three-dimensional ablation data for models of different shapes at stagnation pressures ranging from approximately 0.4 atm to 3 atm and stagnation temperatures equivalent to room temperature. High speed Schlieren photography was used for visualization, and the three dimensional shape change was quantified with sub-millimeter accuracy using laser dot photogrammetry. Experimental results for multiple shapes were compared to those computed using a computational model called ACFD. The ACFD model employed a finite-volume approach to solving the (3-D) Navier-Stokes equations with the gas assumed to be at equilibrium while employing an implicit solver accounting for the material response. By and large, the computational approach was validated for the conditions tested herein. Measurement of ablation rates at the stagnation point yielded approximate values of convective heat transfer rate when conduction through the solid is assumed negligible. The results of this analysis compared favorably to a variety of extensions of the Fay-Riddell correlation given in the literature. Paths for further research were selected and discussed.

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