Modelling spray washing with Lagrangian differencing dynamics

Spray washing is commonly used in car manufacturing to clean and prepare surfaces for subsequent processes like coating and painting. It uses high-pressure spray to deliver cleaning solutions or water onto vehicle surfaces to remove dirt, oils, metal shavings, and contaminants. For optimal washing quality, it is important to have proper nozzle arrangements, spray configuration, and vehicle positioning. Numerical simulations can be used to minimize the trial-and-error process and improve the quality. Spray washing involves strong discontinuities, fragmentation, violent free-surface changes, and complex multiphase flow, which are difficult to simulate using conventional grid-based methods. Lagrangian differencing dynamics (LDD) is a novel numerical method which has the features of being Lagrangian, meshless, and second-order accurate. It employs a meshless finite difference approximation scheme over scattered points and solves the incompressible Navier-Stokes equations in an implicit way. It is suitable for spray simulation because of the Lagrangian and meshless properties. In this work, the spray washing free airless jet validation and simulation of a car body is performed using LDD approach. The LDD solver can accurately predict the cone angle of an airless water jet with a deviation of less than 1.3° from the experimental value. Important information, including fluid reachability and water contact time are obtained from the simulation and the results are analyzed. The influence of nozzle arrangement and configuration are discussed. The final section presents the result of optimizing the nozzles arrangement, which allows achieving complete washing of the car body.