Experiments on Hypervelocity Dissociating Flow over Spheres

This paper presents the experimental results of measurements of the stagnation point heat transfer rates experienced by spherical models of 1, 2, 3, 4 and 6 inch diameter in nitrogen, air and carbon dioxide at stagnation enthalpies ranging from 4 to 22 MJ/kg and stagnation pressures from 25 to 80 MPa. The experimental results are compared with existing results obtained in the ballistic range facility at NASA Ames and also with numerical calculations. The experimental results obtained by optical differential interferometry were compared with the images constructed from flowfields computed using the method of Candler (1988). Good agreement of fringe pattern and shock shape was observed. A novel flow visualization technique using sodium seeding to increase the sensitivity of conventional shadowgraphic techniques by resonant enhancement of the refractivity of the medium was also used. The resonantly-enhanced shadowgraph suggests a possible way of visualizing the vortical structure induced by the strong entropy layer.