Role of wall roughness on energy dissipation and vortex dynamics in self-priming centrifugal pump: A study via entropy generation and Liutex vortex identification

Self-priming pumps are crucial for transporting cooling water to regulate operational temperatures in the petroleum industry, and their energy conversion efficiency significantly optimizes system performance and enhances energy efficiency. Operational factors such as sandblasting, cavitation, scaling, and erosion lead to varying degrees of wall roughness, exacerbating internal flow degradation. This study utilizes an equivalent sand-grain roughness model designed for irregular and non-uniform rough surfaces to rigorously assess the impact of wall roughness on energy dissipation mechanisms through entropy production analysis. Additionally, an innovative Liutex-based method, grounded in the transposed Schur form of the velocity gradient tensor, accurately characterizes vortex structures. Results show that in the fully rough region, pump performance significantly declines, with head and efficiency decreasing by 0.7 m and 4.7 %, respectively, compared to the hydraulically smooth region. The entropy generated in the impeller and volute regions accounts for more than 85 % of the total flow parts, identified as the primary source of energy loss. Under partial load conditions, turbulent entropy production represents over 70 % of the total entropy generation, reaching a maximum of 84 %. As the flow rate increases, the proportion of wall entropy generation rises while turbulent entropy contributions decrease. Meanwhile, comparative analyses demonstrate that the Liutex approach effectively minimizes interference from tension-compression shear effects, capturing both strong and weak vortices. These findings provide strong theoretical guidance for optimizing pump energy conversion capacity and clarify the significant impact of wall roughness on energy loss mechanisms.