Coupled plasma-particle dynamics during low-pressure plasma spraying of 8YSZ on a complex double-airfoil geometry: Effects of gas composition and impingement angle

Achieving uniform thermal-barrier coating deposition on multi-airfoil turbine components remains challenging because substrate curvature, inter-airfoil confinement, and geometric shadowing strongly affect plasma-jet behavior and particle transport. This study numerically investigates low-pressure plasma spraying of 8YSZ particles onto a double-airfoil geometry using a three-dimensional model coupling compressible turbulent plasma flow, Lagrangian particle motion and heating, and particle deposition behavior. Three representative impingement orientations, including leading-edge interaction (Angle 1 = 0°), mid-airfoil interaction (Angle 2 = 90°), and wake interaction (Angle 3 = 45°), were evaluated using two plasma gas mixtures: 30 SLPM (standard liter per minute) Ar + 60 SLPM He and 30 SLPM Ar + 60 SLPM He + 18 SLPM N2. The results demonstrate that impingement orientation has a stronger influence on predicted deposition behavior than plasma composition. Angle 1 maintained the most coherent plasma momentum and thermal structures, producing global maximum deposition rates of 6.86 and 6.96 μm s−1 for Ar + He and Ar + He + N2, respectively. Angle 2 exhibited strong jet splitting and particle bypass, resulting in maximum deposition rates of 0.37 and 0.34 μm s−1. Angle 3 generated wake recirculation and particle-path convergence, producing the highest local deposition rates of 28.75 and 31.59 μm s−1 but with significant spatial variation. Quantitative analysis of sampling locations confirmed that high local deposition rates do not necessarily indicate improved deposition uniformity. These findings highlight that controlling particle accessibility and impingement orientation is critical for optimizing deposition on complex double-airfoil geometries.