This review article examines the last decade of studies investigating solid, molten and liquid particle interactions with one another and with walls in heterogeneous multiphase flows. Such flows are experienced in state-of-the-art and future-concept gas turbine engines, where particles from the environment, including volcanic ash, runway debris, dust clouds, and sand, are transported by a fluid carrier phase and undergo high-speed collisions with high-temperature engine components. Sand or volcanic ash ingestion in gas turbine engines is known to lead to power-loss and/or complete engine failure. The particle-wall interactions that occur in high temperature sections of an engine involve physics and intrinsic conditions that are sufficiently complex that they result in highly disparate and transient outcomes. These particles, which often times are made up of glassy constituents called CMAS (calcium-magnesium-alumino-silicate), are susceptible to phase change at combustor temperatures (1650?), and can deposit on surfaces, undergo elastic and plastic deformation, rebound, and undergo breakup. Considerable research has been put into developing empirical and physics-based models and numerical strategies to address phase interactions. This article provides a detailed account of the conceptual foundation of physics-based models employed to understand the behavior of particle-wall interaction, the evolution of numerical methods utilized for modeling these interactions, and challenges associated with improving models of particle-particle and particle-wall interactions needed to better characterize multiphase flows. It also includes description of a testbed for acquiring canonical data for model validation studies.

Sand particulate ingestion into modern gas turbine engines for fixed wing and vertical lift aircraft is a significant challenge for both military and civilian missions. ARL as part of a DoD funded Laboratory University Collaborative Initiative (LUCI) and Vannevar Bush Fellowship at UCSD are investigating the governing parameters that primarily influences the CMAS adhesion kinetics and infiltration on the standard Yttria Stabilized Zirconia (YSZ) as part of metallic single crystal Nickel superalloys TBC and SiC/SiC CMC T/EBCs. Current research shows various parameters including CMAS viscosity, porosity, adhesion strength, contact angle (wettability factor), geological factors affecting sand formation, coating and structural substrate roughness and surface temperature, internal flow Reynolds number, temperature, pressure, Mach number, boundary layer and bleed air, coating process (columnar vs splat morphology), tortuosity factor et al affects the CMAS adhesion and infiltration. This paper is a summary of our current research to identify and study the governing parameters that affects the CMAS formation, adhesion and infiltration and the underlying interfaces between CMAS and T/EBC, bond coat and the structural substrate. This work is aligned with Army Modernization Priority Future Vertical Lift and PEO Aviation Advanced Turbine Engine (ATE) Program.

In this work, massively parallel wall-modeled Large Eddy Simulations (LES) are conducted to simulate flow through a single stage power turbine sector of a gas-turbine engine under realistic operating conditions. The numerical framework in the current work uses finite volume based compressible CharLES solver that utilizes a moving Voronoi diagram based grid generation. To test grid sensitivity and evaluate the capability of the solver in predicting turbomachinery flows, three grids of varying resolution are used to simulate flow through the baseline gas-turbine under design operating conditions. After assessing the flow solution quality and establishing simulation parameters, LES simulations are conducted to investigate the performance of gas-turbine at off-design conditions. The conditions include the rotor design point at 100% speed, and off-design points at 75%, and 50% speeds subject to high temperatures from the combustor exit flow. The results showed that the internal flow becomes highly unsteady as the rotational speed of rotor deviates from the design point leading to reduced aerodynamic performance. This study demonstrates that the current framework is able to robustly simulate the unsteady flow in a three-dimensional moving rotor environment towards the design of variable speed gas-turbine engines for US Army Future Vertical Lift program.

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