Application of interferometery to supersonic channel flow
The general theory of interference, taking into account the effect of finite source size and spectrum band width is presented in detail and extended to explain the formation of interferograss and operation of the Bach-Behnder Interferometer. An anlysis of the errors, including those due to boundary layers, refraction and finite starters, is made and the uncertainty interval of the instrument is found to be only a few percent, depending on the application. The interferometer is applied to the measurement of of densities in ttwo supersonic channels, and the resulting density contours to those obtained by Characteristic theory, and found to correspond within the interferometer to boundary layer flow is indicated, and the details of the flow in the channels discussed. The use of pressure holes to determins a reference density for interferogram evaluation is investigated, and found to be in order providing that the pressure holes are small and smooth. Total head and for use with a Machmeter are calibrated, and the performance of large angel cones for the measurement of mach number is checked.