1. Ref. 11;In
2. Prior to detailed design definition, the surface shear stress and heat transfer rates were calculated by D.W. Kuntz (Ref, 12), who has developed a cold-wall flat-plate boundary layer code, cfpbl, based on compressible flow boundary layer theory for the laminar boundary layer, and empirical correlations for the turbulent boundary layer. Solutions were computed for a range of achievable HWT flow conditions at Mach 5 and 8. The analytical predictions of the surface shear stress and heat transfer rate were obtained as a function of distance downstream from the leading edge for the flat plate at zero and at -t. 1" angle of attack, Q, (to assess the effect of small experimental departures from zero angle of attack on heat transfer and shear stress) over a range of freestream unit Reynolds numbers and stagnation temperatures. Using the results of those calculations and rough estimates of the length of the transition zone (which influences the axial gradient in surface heat transfer), and assuming the heat transfer is one-dimensional, plate temperature rise as a function of time was computed for a range of plate thicknesses (0.0625-0.250 in.), for several candidate plate materials (stainless steel, aluminum).
3. The results were used to specify the dimensions and material for the flat plate model. It was important to select a plate thickness low enough to yield easily measured backface temperatures but not so high that the clearing temperature (typically, 120 F) would be exceeded in reasonable run times; and to minimize axial heat transfer within the plate, which would violate the one-dimensional heat transfer assumption (thin-wall approximation). At the same time, the plate needed to be thick enough to provide adequate mechanical strength and rigidity against deformation during testing. A satisfactory compromise was found to be a stainless steel (15-5PH) plate of 0.125 inch thickness. The criteria given by George and Reinecke (Ref. 13) were used to estimate the errors due to non-uniform temperature distribution normal to the surface and to axial temperature gradient. These errors were calculated to be negligible for the heat transfer distributions anticipated, and subsequently observed in the experiment. 4 Model Design
4. of the video cameras allowed stop-action exposure times down to 1/2000 sec for each frame and was used to view the model from the side to monitor model motion during testing, especially during tunnel start and shutdown. (Super VHS video equipment, although useful for the higher resolution available, is not required for implementing the LC technique.) The cameras used to record the LC color changes were positioned on the floor below the tunnel and viewed the model through the bottom tunnel window (8 in. W x 15 in. L for the Mach 8 nozzle). The video camera was centered on the model surface approximately 7 in. aft of the leading edge and subtended +/-17 deg. along the plate axis, and 12 deg. side-toside. The still camera was placed approximately 6 in. upstream of the video camera, and subtended a viewing angle ranging from -4 to 30 deg. along the plate and +/- 12 deg. laterally. Single 500-W quartz-halogen adjustable-focus photo floodlamps were arranged fore and aft of the cameras, providing illumination angles for each of approximately 25 degrees. Figure 3 shows the light and camera setup. Figure 4 is a schematic of the experimental system. Test Program