CALCULATION OF NEAR-FREE-MOLECULAR FLUX DISTRIBUTION TO SIMPLE BODIES IN HYPERVELOCITY FLOW
ARNOLD ENGINEERING DEVELOPMENT CENTER ARNOLD AFB TN
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The calculations presented are based on a first-collision model which allows collisions between the free-stream molecules and the molecules which are re-emitted from the surface of the body. The net effect of these collisions is to partially shield the body from the free stream, reducing both the drag and heat-transfer coefficients from the corresponding values experienced in free- molecule flow. Free-stream Mach number is taken to be essentially infinite and the molecules are assumed to be re-emitted from the body surface at the most probable velocity, instead of possessing a velocity distribution. These assumptions enable the distribution of flux to a given body to be expressed as a function of the degree of rarefaction, as represented by the appropriate Knudsen number. This Knudsen number is composed of a characteristic body dimension and the mean free path of the re-emitted molecules relative to free-stream molecules. The integral equation expressing the incident flux distribution on a general body is developed, and solutions are presented for the disk normal to the free stream and for sharp cones of various apex angles, at zero angle of attack. These flux distributions are then integrated to give drag coefficients ratioed to the corresponding free-molecule values.
- Fluid Mechanics