Temperature measurements of shock waves by the spectrum-line reversal method

Abstract

By using a photomultiplier and cathode-ray oscillograph responsive only to changes in light signal, the sodium-line reversal technique, commonly used for measurement of flame temperature has been adapted for time-resolved studies of temperature behind shock waves produced by a bursting diaphragm. The sensitivity of the method is discussed; temperatures can be determined to about ±30°C. General agreement between calculated and observed temperatures is obtained, but both air and oxygen show a high-temperature region due to burning at the interface with the hydrogen driver gas. In nitrogen at around 2400°K, a low-temperature region close to the shock front may be attributed to a vibrational energy lag of the order of 100 μ s, the sodium excitation following the effective vibrational temperature rather than the translational temperature of the nitrogen. In oxygen, evidence for a dissociation relaxation effect is obtained for shocks giving temperatures of around 2500°K; this produces an abnormally high temperature near the front. Other irregularities in temperature in the uniform flow region, especially for nitrogen, are discussed. The period of uniform flow is only about half that expected for a real inviscid gas.