58814 - A Kinematic Study of Individual Rotating Detonation Engine Waves Using K-Means Algorithm 

With growing use of conventional Brayton cycle gas turbines for transportation and power generation and with an increased concern over their adverse contribution to climate change, considerable efforts went into mitigating greenhouse gas emissions and increasing fuel economy through improving thermodynamics efficiencies. However, with conventional gas turbines reaching maturity, any efforts result in small but costly improvements in efficiency. In order to overcome this obstacle and reach much higher efficiencies, a pressure gain combustion (PGC) based thermodynamic cycle is developed. The PGC concept consists of transitioning from a constant pressure Brayton cycle to a constant volume Humphrey cycle resulting in a reduced entropy rise thus enabling the turbine to extract more work. In addition, detonation engines are mechanically simple, have shorter combustion time scales and have the potential to be used as standalone propulsion devices. Of particular interest, the rotating detonation engine (RDE) have demonstrated various key advantages compared to other detonation engines such as the pulse detonation engine (PDE). For instance, RDEs operate on detonation wave constantly consuming fresh reactants providing a continuous flow through the exhaust while PDEs operate relatively slower due to the need of purging combusted reactants. A knowledge gap regarding the fundamental operation of RDEs still exists however, despite feasibility having been realized. The current research is concerned with studying the kinematics of the detonation waves in a RDE by tracking each individual wave and recording its position, velocity, acceleration and peak intensity as it travels around the annulus. The data is extracted through back-end imaging obtained with a highspeed camera by a code developed at the Propulsion and Energy Research Laboratory at the University of Central Florida. The code consists of using a data mining technique, the k-means algorithm, to distinguish each detonation from each other in a particular frame. An algorithm was then developed to match the detonations of a current frame to the ones of a previous frame. Results where then validated using a back-end imaging code developed by the Air Force Research Laboratory. The study consists of two main parts, namely, the mode-locked case and the mode where a transition is about to transition. Back-end imaging was taken from a RDRE and a RDE running on different chemistry and having different geometry. This is done in order to investigate if physical phenomena are consistent across both engines. In the first part, two-waves and three-waves mode-locked cases are analysed to answer the following questions: are the wave speeds acquired by the back-end imaging code the actual individual wave speeds? Are pixel intensities captured by highspeed camera correlate to detonation speeds? Results show that the individual wave speeds differ from the mode-locked wave speed computed by the back-end imaging code. In fact, the waves where found to oscillate around the mode-locked wave speed alternating in dominance. Furthermore, the peak intensities of the waves where found to exhibit similar behaviour correlating to the wave speeds. This is explained by the relative transient detonation height variation occurring in the annulus. In the second part of the study, the waves are followed as the mode is about to transition to both a higher and lower wave count in order to showcase their behavior. Results show that the unstable behaviour witnessed during the mode-locked case is exacerbated as the three wave mode is about to transition to a two wave mode.