| This study investigated a method for direct measurement of skin friction in high-enthalpy shock tunnel tests.; To measure the skin friction, a miniature plastic cantilever floating element skin friction gauge with a natural frequency of 10 kHz was further developed and improved. The cantilever beam is mounted so that the tip of the beam is flush with the wall. The wall shear stress imposed by the fluid results in a lateral force on the beam tip that causes the beam to deflect. Semiconductor strain gauges are mounted at the base of the cantilever to measure the deflection. The beam's small size (6.4 mm long) combined with the light weight of the plastic results in the high frequency response necessary for short duration flows. The cavity surrounding the beam is filled with silicone oil in order in order to thermally isolate the strain gauges, provide vibration damping, and provide a smooth aerodynamic surface.; The miniature plastic cantilever gauge had previously been developed by other researchers but improvements were made to the gauge design, construction, and operation during the course of this research. The goals of the research were to improve the usability and durability of the existing 10 kHz gauge, rigorously assess the accuracy of the gauge, develop a new gauge with higher frequency response, develop and demonstrate a directional sensing capability, and measure skin friction in supersonic combustion ramjet (scramjet) tests undertaken by NASA and the Air Force. Gauge durability was improved by using electronically deposited metallic and ceramic coatings. Methods of preventing oil loss were investigated and improved, and a re-oiling device was designed to improve the usability of the gauge. Potential sources of error were investigated and quantified both analytically and experimentally. A high frequency 30 kHz gauge was constructed by using a miniature I-beam cantilever rather than a round cantilever beam. A directional gauge, capable of measuring, not only the magnitude, but also the direction of the wall shear stress was developed by adding a second set of strain gauges. The directional gauge was demonstrated by measuring the flowfield about a sharp fin in the AFIT high pressure shock tunnel. The baseline 10 kHz gauge and the I-beam gauge were used to measure combustor and inlet wall shear stresses in two sequences of scramjet tests. The first test sequence was conducted at Mach 14 enthalpies at the NASA Ames 16 inch shock tunnel with stagnation temperature of 6,000K and steady run time of 2 msec. The second test sequence was conducted at the General Applied Science Laboratories' Hypulse facility, also at Mach 14 enthalpy and 6,000K stagnation temperature but run time of only 0.4 msec. In addition, a lower frequency gauge was used to measure skin friction in a series of scramjet inlet tests conducted by the Wright Laboratory in the Mach 6 wind tunnel. (Abstract shortened by UMI.)... |
