ЧИСЕЛЬНИЙ АНАЛІЗ ВПЛИВУ ГЕОМЕТРІЇ СОПЛА ДЛЯ ХОЛОДНОГО ГАЗОДИНАМІЧНОГО НАПИЛЮВАННЯ НА ПРИСКОРЕННЯ ЧАСТИНОК

Abstract

Abstract

The subject of this article is the computational analysis of the effect of nozzle geometry on gas dynamics and particle acceleration in cold gas dynamic spraying (CGDS). This study aims to compare the performance of conventional conical nozzles and Method of Characteristics (MOC)-based bell-shaped nozzles in accelerating particles to the critical velocities required for effective coating deposition. The tasks to be solved are as follows: design and model conical and MOC nozzles; conduct CFD simulations of compressible two-phase gas–particle flows in both geometries; analyze velocity, pressure, and temperature distributions along the nozzle and jet regions; and evaluate particle acceleration and velocity distribution for aluminum powder. The following methods were used: numerical modeling of gas–particle flow employing the Navier–Stokes equations with the RNG k–ε turbulence model in ANSYS Fluent 2025 R1, along with Lagrangian particle tracking; computational design of nozzles using MATLAB code based on the Method of Characteristics; and comparison of flow fields and particle dynamics between nozzle configurations. The results show that both nozzles operate under underexpanded jet conditions, but the MOC nozzle accelerates the carrier gas and particles earlier, resulting in more uniform velocity fields and reduced velocity lag between the gas and the dispersed phase. For 25 µm aluminum particles, the MOC nozzle achieves higher particle velocities than the conical nozzle, indicating greater potential for plastic deformation and improved coating adhesion. Additionally, higher exit gas velocities and more stable jet structures were observed in the MOC nozzle, despite the presence of more pronounced boundary-layer vorticity. Conclusions. The scientific novelty of the results lies in establishing the gas-flow acceleration patterns with aluminum powder particles in conical and MOC-based nozzles, optimized for aluminum deposition at 2.5 MPa gas pressure and 650 °C. The MOC-based nozzle enables earlier gas expansion and a more stable free-jet structure, thereby achieving a higher, significantly more uniform powder particle velocity than the conical nozzle under identical spraying conditions.