A combination of computational fluid dynamics (CFD) and Lagrangian particle tracking has been used to predict two-phase erosion-corrosion in a three-dimensional, square-sectioned U-bend. A...

Numerical Prediction of Erosion-Corrosion in Bends

Modelling of erosion–corrosion in practical geometries

Three-dimensional multispecies current density simulation of molten-salt electrorefining

Erosion-corrosion is accelerated corrosion following the removal of protective films. In the past, the majority of erosion-corrosion research has been undertaken using experimental methods. Today, numerical methods provide researchers with an additional tool for investigation. The CFD code PHOENICS has been used to predict hydrodynamic flow fields in a 180° bend and associated mass transfer rates at high Schmidt numbers (Sc = 520) characteristic for corrosion. The k-e two-equation eddyviscosity model for turbulence has been used. To allow for integration through the viscous sub-layer, the LamBremhorst low Reynolds number damping functions were used. Hydrodynamic flow fields and mass transfer rates have been verified against experimental results. Mass transfer rates were directly converted into corrosion rates assuming oxygen limiting mass transfer control. A numerical particle-tracking code has been developed independently in order to predict erosion. The effect of turbulence on particle motion has been accounted for by the use of an eddy interaction model. Tests have been performed on the particle-tracking code to validate the Eulerian statistics. Two erosion models have been integrated into the code and verified against experimental data. Predictions of erosion, corrosion and erosioncorrosion in a three-dimensional square-sectioned U-bend are presented (Re = 5.67 × 10, Rc / D = 3.35). NOMENCLATURE C concentration of species (mol/m) CR corrosion rate (mm/yr) d mass diffusivity (m/s) Dh width of duct (m) dp particle diameter (m) ER erosion rate (mm/yr) k turbulent kinetic energy (m/s) km mass transfer coefficient (m/s) LE eddy length (m) M molecular mass (kg/kmol) m mass (kg) p fluid pressure (Pa) Q volume (m) Rc radius of curvature (m) Re Reynolds number, Re = ub Dh / ν Sc Schmidt number, Sc = ν / d Sh Sherwood numbers, Sh = km Dh / d Sy Yield strength of material (MPa) t time (s) TE eddy lifetime (s) u velocity (m/s) Greek letters α particle impact angle (degrees) e dissipation of turbulent kinetic energy (m/s) ρ density (kg/m) τ shear stress (kg/ms) ν fluid kinematic viscosity (m/s) μ fluid viscosity (kg/m/s)

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Prediction of two-phase erosion-corrosion in bends

The gases flowing inside a solid rocket motor carry alumina particles, which also impact on motor walls and nozzle surface. The particle’s impact on the motor surfaces is predicted to cause damage due to mechanical processes and thermal and kinetic energy transfer from the particle to the surface. Standard ablation prediction models account only to the pyrolysis process of the ablative layers due to the flow of hot gases and hence use empirical correction factors to account for the two-phase flow effects. We develop a model for mechanical and thermal erosion to obtain an improved prediction of the standard ablation prediction models. This model will be used to replace the empirical correction factors by more accurate predictions based on the real physical process of erosion leading to increased observed ablation rates.

Prediction of erosion in a solid rocket motor by alumina particles

Erosion-corrosion is accelerated corrosion following the removal of protective films. In the past, the majority of erosion-corrosion research has been undertaken using experimental methods. Today, numerical methods provide researchers with an addition tool for investigation. The commercial computational fluid dynamics (CFD) code PHOENICS has been used to predict hydrodynamic flow fields and mass transfer rates at high Schmidt numbers (Sc = 520 and Sc = 1460) characteristic for corrosion. The ktwo-equation eddy-viscosity model for turbulence has been used. To allow for integration through the viscous sub-layer, LamBremhorst low Reynolds number damping functions were used. Hydrodynamic flow fields and mass transfer rates have been verified against experimental results. Mass transfer rates were directly converted into corrosion rates assuming limiting mass transfer control. A numerical particle-tracking code has been developed independently. The effect of turbulence on particle motion has been accounted for by the use of an eddy interaction model. Particle dispersion and tracking tests have been performed on the particle-tracking code to validate the Eulerian statistics. Two erosion models have been integrated into the code and verified against experimental data. Using a combination of the PHOENICS CFD code and the particletracking code predictions of erosion, corrosion and erosion-corrosion in a two-dimensional 180 degree bend and a three-dimensional squaresectioned U-bend are presented (Re = 5.67 × 104, Rc/D = 3.35). The effect of particle inertia (hollow glass, sand and copper particles), Reynolds number (Re = 2.1×104, Re = 5.67×104, Re = 1.0×105) and bend orientation (upwards-facing and downwards-facing) on erosion rates, and the effect of diffusivity (Schmidt number) on mass transfer were investigated.

Anthony Keating

Papers

A model for the investigation of two-phase erosion-corrosion in complex geometries