Radiation absorption effects on heating loads encountered during hyperbolic entry.

Abstract

_" 0004-o HARD PLATE V 40PPI WW 0.132 Ib/IN (Tz) O 40PPI WW 0.26 Ity/IN (Tz) A 40PPI WW 0.1975 IbyiN (Tz) 10 30 5O 7O 90 IIO 130 150 I7O 190 210 230 VELOCITY (FPS) Fig. 3 Skin-friction coefficients vs velocity for 40-PPI coating.along the test plate and by calculating the bending moment induced by these pressures. The turbulence intensity of the tunnel ranged from approximately 2% at 20 fps, 0.7% at 05 fps, to 0.3% at 180 fps. Compliant Surface Test SpecimensOne-inch-thick, 27-pores-per-inch (27 PPI) polyurethane foam and -g^-in.-thick, 40-PPI polyurethane foam manufactured by Scott Paper Company and Precision Rubber and Plastic Company, respectively, were used as two of the substrate materials. The third type of compliant coating did not use a polyurethane substrate but used a ^-in. layer of plain water. The substrates were held in place by a shallow aluminum plate with J-in.-thick sidewalls. Each of these test specimens were covered with a 0.0025-in.-thick polyvinyl chloride (PVC) skin (Hooker Chemical Company) similar to that used by Looney and Blick. 1 Water level was adjusted so that the PVC skin was barely touching the resiliant materials under it during the water-saturated foam tests. After installation, various tensions were applied to the PVC skin by means of weights at the front and rear ends and by springs at the sides. Initially weights were used for side tension but this caused excessive vibration of the test plate. ResultsMeasured turbulent skin-friction drag coefficients are shown in Figs. 2-4. The tunnel was operating at 17 to 230 fps. The corresponding Reynolds numbers were 4.4 X 10 5 to 4.8 X 10 6 . Since there was no exact method to determine the characteristic length for a curved tunnel floor, an approximate length of 4.5 ft [Li in Eq. (1)] was used to calculate Reynolds number. Using the following formula: (i) O 0.003 2 O K O = 0.002 O HARD PLATE D PVC WATER SUBSTRATE 0.316 lbf/IN (Tz) 20 30 REYNOLDS NO. (XV/^) x 10 s 10 30 50 70 90 IIO 130 I5O 170 190 210 230 VELOCITY (FPS) Fig. 4 Skin-friction coefficients vs velocity for water substrate coating.the average skin-friction coefficient over the test plate was calculated and was found to fall close to the hard plate experimental data as shown in Fig. 4. Equation (1) was obtained by an integration of the local turbulent skin-friction equation. 3 L 2 in Eq. (1) is the length of the test plate. In Fig. 2, for the dry PVC-polyurethane tests, no data were shown for speeds higher than 86 fps. The PVC skin formed a standing wave at 86 fps. The same reason was true for the cutoff in Fig. 4 for the PVC-water layer tests. No standing waves were observed for water-saturated polyurethane tests.For 27-PPI WW (saturated with water) the highest reduction in C F was 28% below hard plate C F at 100 fps, and for 40-PPI WW the maximum reduction was 38% at 220 fps. The uncertainty in the skin-friction data points in Figs. 2-4 is approximately = 0.0001. ConclusionsAppreciable reduction in flat-plate turbulent airflow skinfriction coefficients has been demonstrated ...