Initial droplet conditions in numerical spray painting by electrostatic rotary bell sprayers
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Initial droplet conditions in numerical spray painting by electrostatic rotary bell sprayers A framework for optimization of injection model coefficients Nico Guettler, Philipp Knee, Qiaoyan Ye, Oliver Tiedje
The Author(s) 2020 Abstract In computational fluid dynamics, the modeling of paint application processes by electrostatic rotary bell sprayer is mostly performed using an Euler– Lagrange approach. The initial conditions of the discrete phase—position, velocity, size, and charge— have an essential influence on the resulting film thickness distribution and the total charge transferred to the object. Typically, so-called injection models are used to specify these initial conditions, whereby the determination of the injection model coefficients is crucial. In this paper, a framework is proposed that combines experimental input data, an injection model, and a metamodel-based optimization. The painting tests for the generation of input and validation data were carried out in a technical center in the industrial standard. The simulations were performed using ANSYSFluent. Initial droplet conditions could efficiently be determined via the framework so that the painting-specific objectives were achieved with reasonable accuracy. In addition to the framework, a turbulence study of the strongly swirled shaping air of this atomizer was carried out, whereby a substantial underestimation of the axial air velocity was found in the turbulence models being investigated. The initial droplet conditions were also used in this study to draw conclusions about the accuracy of the airflow simulation. The proposed framework can be adapted to other solvers and efficiently finds injection model coefficients for other paint applicators. Keywords Spray painting simulation, Rotary bell atomizer, Electrostatic painting simulation, Metamodel N. Guettler (&), P. Knee, Q. Ye, O. Tiedje Fraunhofer Institute for Manufacturing Engineering and Automation IPA, Nobelstrasse 12, 70569 Stuttgart, Germany e-mail: [email protected]
Introduction Numerical simulations of paint application processes are used for virtual operating trials to perform paintability studies in early design phases, to optimize process parameters, and to reduce the number of painting prototypes. To reduce the computational effort and increase the accuracy of painting simulations, both numerical and painting-specific models and methods must be continuously enhanced. Particularly in spray simulations, the Euler–Lagrange approach requires injection models to determine the initial conditions—position, velocity, size, and charge of the particles. In this study, an electrostatic rotary bell sprayer (ERBS) was used, which is being used in the automotive industry to paint car bodies and plastic parts like bumpers. When using ERBS, paint is stationary added inside the bell-cup through a small orifice on the rotation axis. Due to the rotational speed of the bell-cup, the paint is distributed radially on the inner surface by centrifugal forces. At the bell-edge, the paint is
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