Validation of Cross-Correlation Detonation Wave Mode Identification Through High-Speed Image Analysis

Abstract

Various techniques have been developed to characterize the modal properties of the detonation waves that occur in rotating detonation engines (RDEs). Primary techniques for defining the wave speed, number of waves, propagation direction and mode (co- vs counter-rotating) have included analysis of high-speed imagery, as well as frequency based and time of flight correlations of transducer signals such as dynamic pressure or flame ionization (chemi-ionization). Although high speed imagery (even in the visible spectrum) can provide insightful quantitative data regarding the performance of the detonation wave(s), it can be challenging to acquire in an application that would have both upstream and downstream turbomachinery. For these applications, transducer-based methods coupled with signal processing methodologies to characterized operation may be more appropriate. While transducer-based methods are well understood, they often rely on assumptions to draw physical conclusions and verification of their ability to quantify the desired properties must be performed. Previous studies have proposed the use of a cross-correlation method to measure wave properties and modes in an RDE. While these techniques appear to have proposed logical results they rely on underlying assumptions, such as an assumed Chapman-Jouguet wave speed, to quantify detonation wave properties and modes, some means of verifying their performance must be considered. This study will utilize a modified version of an automated image process method developed at the Air Force Research Laboratory (AFRL) in which to validate a previously published multi-transducer cross-correlation algorithms used to characterize the operational state of an RDE. Calculated wave number and wave speeds are compared across a modal change to evaluate agreement between techniques as well as individual strengths of each.