Free-Flight Measurements of Stagnation-Point Convective Heat Transfer at Velocities to 41,000 Ft/Sec
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION MOFFETT FIELD CA AMES RESEARCHCENTER
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Measurements of stagnation-point convective heat-transfer rates in air at velocities to 41,000 ftsec, are presented. A new technique was developed at the Ames Research Center to make these measurement. In this technique, 14-inch-diameter aluminum hemispheres are gun launched into the prototype of the Ames hypervelocity free-flight facility at a velocity of 24,000 ftsec into still air, and at combined velocities of 36,000 and 41,000 ftsec into the countercurrent airstream. At some point on its flight path the model begins to melt, and molten aluminum streams from the model surface into the wake, where it can be seen in spark shadowgraphs. The stagnation-point heating rate is then deduced by computing the heating rate required to produce melting at the observed time. The low-speed tests at 24,000 ftsec served as calibration tests for the technique and showed its workability. To study the possible effects of model material on the convective heating rate, several of the aluminum models were plated with a 0.0005-inch-thick nickel shell. These models were also subjected to calibration tests and then used for measuring convective heating rate at a velocity of 36,000 ftsec. The heating rates measured from all of the tests agree reasonably well with each other and with the majority of shock-tube data, and support theories which predict that ionization effects on convective heating rates in air will be small. No differences in heating rate were found for the two model surface materials tested.
- Fluid Mechanics