The Experimental Determination of the Thickness of a Shock Front in a Gas

Equations are developed from which the density profile of a shock front may be calculated from a knowledge of its reflectivity as a function of wave-length and angle of incidence. The reflectivities of shock fronts of shock pressure ratio p2/p1=1.71 have been measured in nitrogen at initial pressure, p1, equal to 85, 68, and 42 lb./in.2. From the change of reflectivity with wave-length, the thickness of the fronts was found to be 1.8×10−5 cm, 2.0×10−5 cm, and 3.2×10−5 cm with an accuracy of twenty-five percent. An independent but less accurate check was provided by the change of reflectivity with initial pressure, yielding a thickness of 1.5×10−5 cm for p1=85 lb./in.2. The weighted mean value, 1.7×10−5 cm, for p1=85 lb./in.2 is significantly greater than that calculated from the theory of Thomas, 1.0×10−5 cm.