Efficient Large-Scale Coating Microstructure Formation Using Realistic CFD Models
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Thomas Wiederkehr and Heinrich Mu¨ller (Submitted March 12, 2014; in revised form July 1, 2014) For the understanding of physical effects during the formation of thermally sprayed coating layers and the deduction of the macroscopic properties of a coating, microstructure modeling and simulation techniques play an important role. In this contribution, a coupled simulation framework consisting of a detailed, CFD-based single splat simulation, and a large-scale coating build-up simulation is presented that is capable to compute large-scale, three-dimensional, porous microstructures by sequential drop impingement of more than 10,000 individual particles on multicore workstation hardware. Due to the geometry-based coupling of the two simulations, the deformation, cooling, and solidification of every particle is sensitive to the hit surface area and thereby pores develop naturally in the model. The single splat simulation employs the highly parallel Lattice-Boltzmann method, which is well suited for GPUacceleration. In order to save splat calculations, the coating simulation includes a database-driven approach that re-uses already computed splats for similar underground shapes at the randomly chosen impact sites. For a fast database search, three different methods of efficient pre-selection of candidates are described and compared against each other.
Keywords
3D, lattice boltzmann method, microstructure formation, particle impact simulation
1. Introduction In thermal spraying, the feedstock material provided as rods, wires, or powders is melted and resulting liquid material particles are accelerated toward a surface to be coated. Upon impact, the particles flatten, rapidly cool down, and solidify on top of each other thereby forming a complex coating microstructure. Due to entrapped gas in between the solidified splats a complex porous microstructure develops over time. Geometric models of such thermally sprayed microstructures are used in a wide variety of simulations to predict different physical properties of the manufactured workpieces that are relevant for the application at hand. Examples include the investigation of residual stress distributions, elastic modulus, fracture toughness, erosion resistance, or heat transfer for thermal barrier coatings (Ref 1-4). In practice, obtaining adequately complex and realistic three-dimensional microstructure models is a difficult and time-consuming task. In this work, a novel, generic, computationally efficient simulation concept is presented that is suited to be combined with different single-particle simulations providing three-dimensional splat shapes to construct the whole coating. The concept is found on the Thomas Wiederkehr and Heinrich Mu¨ller, Technische Universita¨t Dortmund, Informatik VII - Graphische Systeme, Dortmund, Germany. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
finding that single splat formation algorithms have been extensively studied in the literature in the last years, but only few publications mention ‘‘st
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