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INTRODUCTION
The present work extends the analysis presented in Part I of this study [1], hereafter referred to as Part I, and investigates the interfacial and flow dynamics of binary droplet collision of unequal molten sand particles. Sand and dust particles are routinely ingested in rotorcraft gas-turbine engines, especially during take-off and landing when operating in desert environments. While provisions such as particle separators are installed at the inlets, small particles (< 50 μm) are often entrained and reach the combustor. Due to the high operating temperature in the combustion chamber, these particles, in the form of calcium–magnesium–alumino–silicate (CMAS), melt [2, 3, 4]. The undesired entrainment and melting of CMAS particulates is detrimental to the entire engine starting from the compressor to the turbine and causes the loss of efficiency and surge margin in the compressor, clogging of the fuel spray nozzles in the combustor, and clogging of the nozzle vanes and cooling channels in the turbine hot section [3, 5, 6]. The next-generation hot-section material technology based on silicon carbide (SiC) fiber-reinforced SiC/SiC ceramic matrix composites (CMCs), while thermally superior to nickel-based superalloys [7], is susceptible to corrosion from combustion gases and impact from molten CMAS particles, is often coated with environmental [8, 9] and thermal barrier coatings (E/TBC) [3, 10]. Current coatings are effective to 2400 F; however, as combustor temperatures increase to improve efficiencies, next-generation E/TBCs need to be developed that are effective at 3000 F and higher temperatures. Specifically, it is critical to understand the size distribution of CMAS particles leaving the combustion chamber and impacting the hot-section material components to design the coating materials. Molten CMAS droplets in the combustion chamber can undergo stretching, breakup, coalescence, and agglomeration, and these dynamic behaviors determine the shape and size distribution of particles that impact the downstream components in the flow path. Therefore, a detailed understanding of these behaviors and the resulting distributions is imperative, as we develop coatings for future rotorcraft engines.
Much progress has been made on understanding the deposition characteristics and particle trajectories in gas-turbine hot sections [5, 11, 12, 13, 14, 15]; however, limited literature is available for the phenomenon of droplet–droplet interactions of CMAS, while they are still in the combustor. Knowledge of droplet interaction and phenomenon is...