Detection of shock and detonation wave propagation by cross correlation

The propagation speed of a shock or detonation wave in a shock tube is usually determined by a time-of-flight method by dividing the distance between two transducers with the propagation time of the disturbance signal. Some arbitrariness is inherent in determining the propagation time by this method. An improved method for objectively determining the propagation time using a nonstationary cross-correlation technique is described. The method requires the choice of an integration window that includes the nonstationary event. The method was first tested against a number of model functions with different noise levels. It was then applied to propagating and reflected shock and detonation waves, including an example of a transitioning detonation wave propagating past six transducers. In addition, the nonstationary CCF technique was also applied to evaluate the uncertainty in estimating the deflagration-to-detonation transition run-up distance. In all cases, the time delay and its standard deviation could be obtained.