The purpose of this paper is to provide a method of the paint thickness simulation for robotic painting of curved surfaces based on the Euler-Euler approach in CFD theory. The Euler-Euler approach is proposed to be adopted to simulate the paint deposition process of painting curved surfaces with a moving spray gun in this paper. The paint deposition model established comprises two parts: a two-phase spray flow field model and a film model. The method of solving the model is also provided. In order to demonstrate the capability of the proposed method, three cases were simulated and experimented including painting a flat plate, an outer cylindrical surface and an inner cylindrical surface. It was found that the peak of the film thickness distribution on the inner cylindrical surface is the largest followed by that on the flat plate and that on the outer cylindrical surface. The film width of painting the inner cylindrical surface is wider than that of the outer cylindrical surface and the flat plate. The experimental results were in a reasonable agreement with the simulation results, which indicates the simulation method based on the Euler-Euler approach in CFD theory proposed in this paper to be effective and applicable in simulating the paint thickness for robotic painting of curved surfaces.

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The test studies the gas-liquid two-phase flow characteristics in pump-assisted evacuation process for hillyterrain pipeline system. In pump-assisted evacuation process, there appear two flow patterns: stratified flow and slug flow. By means of reducing upstream back pressure, the pump-assisted evacuation can increase the liquid flow rate, promoting the transition of flow pattern. For the pipe-bottom pressure change process, it increases firstly, then decreases, and slowly increases at last. During the process of pressure drop, there will appear temporary buffer section for the slug accumulation. The pressure fluctuation doesn't increase with inlet superficial gas velocity, and the max fluctuation range appears in the working condition with 0.88m/s superficial gas velocity. The outlet liquid flow rate corresponds to the pressure fluctuation. Four stages are divided for the variation process. The flow rate is less influenced by the inlet superficial gas velocity, but more influenced by the inclined angle. By using gas front-end velocity meter to check the evacuation efficiency, it is found that with inclined angle of upward inclined pipe (UIP) unchangeable, the higher the gas superficial velocity, the greater the gas front-end velocity, presenting an approximate linear relationship; with the gas superficial velocity unchangeable, the gas front-end velocity almost remains the same, even with the inclined angle of upward inclined pipe increasing.

Painting a V-shaped surface, which is widely found in various facilities and equipment, often results in poor coating quality, which may be caused by an insufficient understanding of film-forming characteristics and mechanism. In this study, computational fluid dynamic (CFD) simulations were carried out for in-depth research on the film-forming characteristics and mechanism of painting V-shaped surfaces. The mathematical model of film formation was established with the Euler–Euler method, and the unstructured grids and adaptive-mesh refinement were adopted to discretize the computational domain. By solving the model, the coating thickness distribution law and flow-field characteristics of spraying a V-shaped surface were obtained. When painting a V-shaped surface with an angle less than 180°, the coating thickness distribution appeared as two peaks, instead of the single peak that appeared when painting a flat wall. As the V-shaped angle decreased, the coating thickness became thinner. The peak position gradually shifted to both sides, and the thickness distribution became wider. Analysis of the spray flow-field characteristics revealed the thickness distribution mechanism, by whichthe geometric characteristics of the V-shaped surface changed the near-wall distribution of the flow field. When the V-shaped angle decreased, the pressure peak at the center of the V-shaped surface and the eccentric pressure peaks that formed on both sides increased. The near-wall paint fluid was confined between the central pressure peak and the off-center pressure peak, resulting in paint droplets depositing between the pressure peaks and double-peak distribution of the coating thickness forming on the V-shaped surface. The spraying experiments verified the correctness of the numerical simulations, film-forming characteristics, and corresponding mechanism, which are of great significance for efficient and high-quality spraying on V-shaped surfaces.

This paper investigates the water-oil displacement flow in a downward inclined pipe, which is applied in practice in the chemical and oil industries. The computational fluid dynamics (CFD) method was applied in the simulation of the displacement process. The simulation procedure was performed in a structured grid with refinement near the boundary, and the Volume of Fluid method was used as the multiphase model. Three flow patterns were obtained and the simulated data were favorably matched with the experiment results. Further efforts were made where parametric studies were concerned, including the effects of pipe diameter, inclination angle, and water inlet velocity on the displacement process. It was concluded that the displacement efficiency can be improved by increasing the water inlet velocity, and the increasing pipe inclination angle may lead to the instability of the interface.