Abstract:
Summary. Tests have been made on the N.P.L. low-density tunnel on two pressure-plotting cones of 15 deg and 30 deg semi-vertex angle placed at zero incidence to the flow. The stream static pressure was varied between 20 and 80 microns of mercury, giving Reynolds numbers, based on a model length of 1.25 inches and free-stream conditions, of from 81 to 372. The tunnel Mach number varied between 1.92 and 2.24 as the tunnel static pressure changed. On the forward-facing surfaces the local pressures are higher than those for inviscid flow and it is shown that this viscous-interaction effect can be reasonably well predicted by a simple theory using a tangent-cone technique. The base pressures on both cones were measured and the results agree well with data obtained earlier by Kavenau. The flow behind the model was explored in a simple manner and is shown to resemble that obtained on blunt-based bodies at higher Reynolds numbers. The tips of both models were progressively blunted by means of truncations normal to the cone axes, and the changes in the surface pressure distributions were measured. For the cone with a 30 deg semi-vertex angle these changes were quite small. Some details of the tunnel operating technique and the instrumentation (including the thermistor pressure-measuring system) are given in an Appendix.
