Simulation of the film formation at a high-speed rotary bell atomizer used in automotive spray painting processes
The present contribution summarizes investigations aiming to calculate the two phase flow field inside the manifold of a rotary bell atomizer and the free film on the rotary bell surface. Calculations are based on the CFD code Fluent using the Volume of Fluid (VOF) method. The phase distribution in the bell's manifold as well as the film thickness on the bell was determined, the latter result being compared with an analytical solution also. The simulations were carried out on a CRAYOpteron Cluster available at the Hochleistungsrechenzentrum HLRS of the University of Stuttgart. It was found that the paint flow is emerging from the paint nozzle forming a relatively thick film on the so-called distributor disk. The blockage of the distributor disk mount (3 separate bolts) leads to a paint flow from the distributor disk to the inner surface of the bell. The major paint fraction, however, leaves the distributor surface at the edge of the horizontal channel, further flowing along the bell surface towards the bell edge. However, finally a stable film is formed on the bell surface. Here, the estimated film thicknesses from the VOF simulations coincide very well with results from an analytical solution. Consequently, bubble formation in the paint, which is one of the reasons for these investigations, can only take place in the mixing zone between paint nozzle exit and distributor disk, where the paint jet impacts on the distributor disk surface. In the future, the investigations will be extended to calculate jet formation and disintegration.