ICLASS 2012, 12 th Triennial International Conference on Liquid Atomization and Spray Systems, Heidelberg, Germany, September 2-6, 2012 Simulation of Electrostatic Rotary Bell Spray Painting in Automotive Paint Shops A. Mark ∗1 , B. Andersson 1 , S. Tafuri 1 , K. Engström 1 , H. Söröd 2 , F. Edelvik 1 , J. S. Carlson 1 1 Fraunhofer-Chalmers Centre, Chalmers Science Park, Gothenburg, Sweden 2 Swerea IVF, Mölndal, Sweden andreas.mark@fcc.chalmers.se, bjorn.andersson@fcc.chalmers.se, sebastian.tafuri@fcc.chalmers.se, klas.engstrom@fcc.chalmers.se, henrik.sorod@swerea.se, fredrik.edelvik@fcc.chalmers.se, johan.carlson@fcc.chalmers.se Abstract A new framework for simulation of electrostatic spray painting is proposed based on novel algorithms for coupled simulations of air flow, electromagnetic fields and paint droplets. Particularly important for the computational efficiency is the Navier-Stokes solver. The incompressible solver is based on a finite volume discretization on a dynamic Cartesian octree grid and unique immersed boundary methods are used to model the presence of objects in the fluid. This enables modeling of moving objects at virtually no additional computational cost, and greatly simplifies preprocessing by avoiding the cumbersome generation of a body conforming mesh. To validate the sim- ulation framework an extensive measurement campaign has been performed. Several test plates and car fenders were painted with different process conditions and robot paths. The same cases were then simulated and overall the agreement between simulations and experiments are remarkably good. The very efficient implementation gives a major improvement of computational speed compared to other approaches and makes it possible to simulate spray painting of a full car in just a few hours on a standard computer. Introduction The paint and surface treatment processes in automotive paint shops are characterized by multi-phase and free surface flows, multi-physics, multi-scale phenomena, and large moving geometries. This poses great challenges for mathematical modeling and simulation. The current situation in the automotive industry is therefore to rely on in- dividual experience and physical validation for improving these processes. Having access to tools that incorporate the flexibility of robotic path planning with fast and efficient simulation of the processes would be advantageous, since such tools can contribute to reduce the time required for introduction of new models, reduce the cycle-time, reduce the environmental impact and increase quality. In this paper the focus is on spray painting with the Electrostatic Rotary Bell Sprayer (ERBS) technique. Paint is injected at the center of a rotating bell; the paint forms a film on the bottom side of the bell and is atomized at the edge. The droplets are charged electrostatically and driven towards the target both by shaping air surrounding the rotating bell and by a potential difference in the order of 50-100 kV between paint applicator and target. A few attempts to simulate the complex process can be found in the literature [1, 2, 3, 4]. In particular, Domnick et al. have made extensive modeling work for wet paint as well as for powder coating devices [5, 6]. A systematic validation for realistic geometries is missing and another major drawback with earlier approaches is that the simulation times are prohibitively long for the tools to be industrially useful. This is partly due to the fact that the simulation methods do not handle moving geometries in an efficient way. The aim of this paper is to present a new framework that allows for accurate simulations of spray painting of a car in just a few hours on a standard computer. To achieve this, novel algorithms are developed for coupled simu- lations of air flow, electromagnetic fields and charged paint droplets. Particularly important for the computational efficiency is the Navier-Stokes solver. Unique immersed boundary methods are used to model the presence of objects in the fluid and they are combined with an adaptive Cartesian octree grid [8, 9]. This enables modeling of moving objects at virtually no additional computational cost, and greatly simplifies preprocessing by avoiding the cumbersome generation of a body conforming mesh. The electrostatic solver is based on the same discretization framework and immersed boundary conditions are used to set the voltages at the applicator and target geometry. The paint droplets are simulated as Lagrangian particles and their motion is given by the Basset-Boussinesq-Oseen (BBO) equation. To validate the simulation framework an extensive measurement campaign was performed. The droplet size distribution, and the air and droplet velocities close to the bell, were measured for different process parameters us- ing a Malvern and laser doppler anemometry (LDA), respectively. The break-up process is currently not simulated ∗ Corresponding author: andreas.mark@fcc.chalmers.se 1