Particle ingestion into modern gas turbine engines is known to reduce performance and may damage many primary gas path components through erosion or deposition mechanisms. Many studies have been conducted that evaluate the effects of particulate ingestion in primary and secondary gas path components. However, modern gas turbines have gas path temperatures that are above most previous studies. As a result, this study performed particle deposition experiments at the Virginia Tech Aerothermal Rig facility at engine representative temperatures. Arizona Test Dust of 20 to 40 μm was chosen to represent the particle ingested into rotorcraft turbine engines in desert and sandy environments. The experimental setup impinged air and sand particles on a flat Hastelloy X coupon. The gas and sand mixture impacted the coupon at varying angles measured between the gas flow direction and coupon face, hereby referred to as coupon angle. For this study, gas and sand particles maintained a constant flow velocity of about 70 m/s and a temperature of about 1100°C. The coupon angle was varied between 30° to 90° for all experiments. The experimental results indicate sand deposition increased linearly from about 975 °C to 1075 °C for all coupon angles. A multiple linear regression model is used to estimate the amount of deposition that will occur on the test coupon as a function of gas path temperature and coupon angle. The model is adequate in explaining about 67% of the deposition that occurs for the tests. The remaining percentage could be explained with other factors such as particle injection rates and exact surface temperature where the deposits occur.

Deposit formation on turbine hardware in propulsion turbine engines can occur in many arid regions globally. Characterising crystalline deposits on metallic substrates can aid in component resilience and health monitor algorithms during particle ingestion. This study has developed two statistical empirical models for prediction from acquired experimental data for the onset of deposits. The prediction models are for crystalline particulate (Arizona Road Test Dust) deposits on a flat rectangular Hastelloy-X test coupon. Particle impingement angles varied between 20° and 80° in experimental flow temperatures of 1,000–1,100°C. Averaged deposits are methodically quantified through normalised particle deposit tallies per area and percent coverage of the surface using microscopic imaging and image processing programs. Deposit accumulation is a quadratic function of both near-surface coupon temperature and coupon angle.

A hot sand model has been developed to predict the rebounding and sticking behavior of environmental particulates in the hot section of a gas turbine. This paper will focus on the sticking part of the model with rebounding effects to be discussed in a future paper. The key element of the model is determining the probability of the particle sticking to the surface when it comes into contact. Recent studies have suggested this sticking probability is a function of temperature, particle size, normal and tangential velocities of the impacting particle. Previous studies have predicted the sticking probability using theories for mechanical properties of the particles. These methods rely on idealized particle shapes and compositions which does not match the variable nature of sand in the environment. The current model attempts to take this randomness into account and ensure prediction accuracy by matching the model to results of a series of controlled coupon tests. The framework for the modeling approach and validation results of the developed predictive model are both presented.

Deposition experiments are performed on a Hastelloy-X coupon using Arizona Road Test Dust (ARD). A statistical empirical model of the initial onset of ARD deposits is developed from the experimental data. The initial onset of deposits are a quadratic function of local surface temperature and impact velocity components (normal and tangential). A prominent observation is that tangential impact velocity has a significant non-linear, independent effect on deposits relative to normal impact velocity and local surface temperatures. All experiments use 20–40 μm ARD on a bare metal surface over a 1000–1100°C range. Unlike prior mass-based deposit studies, initial deposits for this study are quantified using a Coverage Ratio (CR), which is the area covered by deposits relative to the total area available. The empirical CR model has a strong correlation to coupon surface temperature and impact velocity vectors and is a foundation for future numerical or experimental model comparisons.

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