Explore the fundamentals of erosion and the cutting-edge simulation techniques that help predict and mitigate its impact on industrial equipment.
Erosion Basics
Erosion is the process by which material is removed from a wall surface due to micromechanical deformation or cracking of the wall’s surface. In fluid-carrying equipment (such as gas and water turbines, pumps, heat exchangers, and so on), surface erosion is caused in part by the impact on equipment walls by solid particles entrained within a fluid flow.
Eventually, wall erosion leads to equipment degradation, decreasing the performance, and reduced service life. This particle-wall interaction can lead to various material removal mechanisms, including:
- Micromechanical deformation: Repeated impacts cause localized plastic deformation, fatigue, and eventual material loss.
- Cutting or scraping: Sharp particles can remove material through a cutting action.
- Brittle fracture: High-velocity impacts can cause instantaneous crack formation and chipping in brittle materials.
- Surface fatigue: Cyclic loading from repeated impacts can lead to fatigue crack initiation and propagation.
The severity of erosion depends on several factors, including:
Particle properties (size, shape, hardness, and concentration)- Fluid properties (density, viscosity, and corrosiveness)
- Flow characteristics (velocity, turbulence, and angle of impact)
- Wall material properties (hardness, ductility, and microstructure)
These effects result in:
- Decreased performance and efficiency
- Increased maintenance requirements
- Reduced service life
- Potential for catastrophic failure
Simulation Approach
Different industries are exposed to the potential mechanisms that could cause significant erosion damage like: Particulate erosion, Liquid droplet erosion, Erosion-corrosion and Cavitation. Computational Fluid Dynamics (CFD) simulations play a crucial role in predicting and mitigating erosion by:
- Modeling particle trajectories and impact characteristics
- Estimating erosion rates and patterns
- Optimizing equipment design to minimize erosion-prone areas
- Developing erosion-resistant materials and coatings
Ansys provides different gas-liquid-solid flow modeling capabilities for a wide range of particle sizes and loadings. One of those capabilities is the Discrete Phase Modeling (DPM) available in Ansys Fluent. DPM is a method that tracks dilute, dispersed secondary phases such as solid particles, liquid droplets, or air bubbles. The secondary phases must satisfy the requirement of having a volume fraction less than 0.10.
Discrete Phase Modeling
Discrete Phase Model (DPM) is used to track dilute, dispersed secondary phases such as solid particles, liquid droplets, or air bubbles using the Lagrangian method. Erosion modeling within Fluent can be performed using DPM to predict the erosion rate on surfaces due to particle impacts. The DPM provides validated solid-particle flow modeling capabilities for a wide range of sand particle sizes and loadings, and it includes a variety of industry-accepted erosion models:
- Finnie Erosion Model: For ductile materials.
- Oka Erosion Model: For ductile and brittle materials.
- McLaury Erosion Model: Developed for O&G applications.
- DNV Erosion Model: For offshore and marine applications.
- Erosion Model in Dense Flows: Includes the effects of high particle concentrations.
- Accretion: Material removal and deposition in certain applications.
How it works
Erosion Analysis is a Post Processing exercise during Fluent simulation. Ensure proper convergence of flow field with proper turbulence model and near wall treatments. Finer mesh near wall helps with predictions. Erosion analysis also depends on particle information and proper postprocessing setup. The moleding approach in Ansys Fluent follow these steps:
- Particle trajectories are calculated using coupled DPM simulation. Particle-wall interaction are defined through coefficient of restitutions for normal and tangential directions.
- When individual particles impact on a wall the damage done is calculated using a impact damage model (default erosion model).
- Predicted erosion locations and erosion scar shapes are shown. This is particularly advantageous in complex geometries such as valves, in which particle trajectories are very convoluted and complicated
Advanced Modeling
Alternative models for multiphase systems use the Euler-Euler approach instead of the Euler-Lagrange method from the Discrete Phase Model (DPM). The Euler-Euler models and the Dense Discrete Phase Model (DDPM), which combines both approaches, are discussed in Modeling Multiphase Flows. These models in Ansys Fluent are valuable for simulating particle-laden flows and analyzing erosion. The DDPM is particularly effective in scenarios like Fluidized Beds, where particles may settle and accumulate due to gravity.
Coupling with more tools
- Moving Dynamic Mesh (MDM)
This capability allows the simulation of wall deformation due to particle-induced erosion. This is particularly useful for capturing the effects of erosion on the flow pattern and the structural integrity of equipment. The MDM enables quasi-automatic mesh deformation setup for all participating walls, and the simulation is driven by the mesh deformation time step, which is determined by the allowable cell deformation. However, it uses a steady-state fluid solution
- Discrete Element Method (DEM)
The DEM allows simulating the material erosion and degradation due to particle impacts. This module does not change the surface of the geometry. Rather, it calculates the cumulative eroded mass associating it to a boundary-triangle property that can later be post-processed. The API solvers allow implementing various erosion models and surface grid deformation to simulate wear patterns on surfaces.
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