Shock Structure of a Spherical Projectile in Weakly Ionized Air
ARNOLD ENGINEERING DEVELOPMENT CENTER ARNOLD AFS TN
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A test program was undertaken at Arnold Engineering Development Center AEDC to investigate previously reported measurements of anomalous shock standoffs in weakly ionized gases by installing an RF plasma generator in AEDCs S1 Hypervelocity Impact Range. The AEDC tests were conducted by firing 9.5- and 19.1-mm-diam spheres in air at velocities in the range 1200 to 1700 msec and at pressures in the range 15 to 40 torr. The bow shock shape data were obtained using holographic interferometry techniques. A standoff distance was measured and ratioed to the projectile radius. The data were compared to CFD calculations for a uniform gas temperature. Confirmation of the anomalous shock standoffs was obtained, and efforts were subsequently directed towards separating the effects of ionization from the effects of gas temperature on the shock profile. The temperature was measured by three different techniques thermocouple, N2 emission spectrum, and NO-PLIF the results appear to be much lower than necessary to explain the measured shock standoffs by uniform gas effects.
- Fluid Mechanics