A Computational Analysis of the Aerodynamic Effects on Particles Flowing From a Duct

Abstract

This work studies the design of a device conveying dust and sand in order to understand how the particles impinge, erode and rebound from a target plate. The motivation behind this study is understanding dust ingestion and erosion in aviation gas-turbine engines. Erosion in engines due to surface impact is an important factor contributing to their reduction in performance. Ingestion of small particles such as sand, ash and ice cause harm to the engine, which can eventually lead to engine failure. The trajectory and size of the particles play an important role in predicting the damage occurring in the engine. In this study, a system is designed to deliver particles at a certain concentration and velocity to a target plate. The purpose of the target plate is to study particle damage on a surface. The domain consists of a constant area duct in which particles are injected in the upstream direction using a particle seeder. The particles exit the duct through a converging nozzle where they are accelerated to the desired exit conditions. One of the criteria of the particle injection system is that it is designed to ensure that the particles are concentrated in the center of the constant area duct, reducing erosion along the walls. This motivates the need for the particles to be conveyed with minimal rebounds within the duct, as excessive rebounds would reduce the particle velocities and potentially lead to particle fragmentation. The computational fluid dynamics (CFD) model is developed to influence and guide the design of an experimental rig. This rig will be used to analyze particle trajectories as well as impact and rebound speeds from the target. Another goal of the rig is to provide an insight into particle fragmentation after impact. Having good CFD predictions of the particle aerodynamics prior to impact with the target is critical to ensuring that the CFD simulation data is able to provide results that will ensure the reliability of the experiments. This research analyzes the aerodynamic effects of the flow on particles of various sizes as they impact a target surface. Particles respond differently to changes in the flow field based on their diameter, and so a discussion about their diameters is relevant. The smallest particle sizes follow the streamlines and act as tracers, while the larger particles tend to be more ballistic and are mostly unaffected by the change in flow. The angle of the target plate is also varied to observe the effects on the incoming particle trajectories. The variation in angle leads to different flow fields forming upstream of the target plate which in turn affects the particle dynamics as well as their impact and rebound properties. These studies are conducted to gain an understanding of how the dynamics of particle size and target plate angle affects the impact velocities and erosion. Two exit Mach Number (Mexit = 0.25, 0.7) configurations with particle diameters ranging from 20 micrometers to 200 micrometers are run to influence upcoming experiments. The aerodynamic effects on the particles near the target plate are analyzed and compared at these configurations. The CFD simulations are conducted using a commercially available software, StarCCM+. The flow physics and particle motion are analyzed using Reynolds Averaged Navier Stokes (RANS) CFD techniques coupled with a Lagrangian particle tracking model. A 2-equation realizable k-ε RANS simulation is chosen to model the turbulence physics; the gas phase is two-way coupled to the Lagrangian particle phase. The Lagrangian equations calculate the drag around the particles using the Holzer-Sommerfeld correlation, and use the Sommerfeld correlation to calculate the Shear Lift Force.