CFD-based analysis for finding critical wall roughness on centrifugal pump at design and off-design conditions

Three-dimensional numerical analyses were conducted to study fluid flow behavior over the rough surface in an electric submersible pump at the design and off-design conditions. The entire range of smooth, transition and fully rough surfaces was considered for the study of the turbulent boundary layer properties and its effect on the pump performance. The calculated performance using CFD showed a good agreement with the experimental data. For wall-bounded turbulent flow through a pump passage, the k–ω SST turbulence model was used along with automatic wall function. To study wall roughness effect at the design and off-design conditions, the parameters such as flow rate, impeller speed and roughness factors were varied. Strong interaction between the rough wall and fluid changes the pressure, velocity gradients and turbulence parameters within boundary and affects the overall pump performance. The result showed that performance initially reduced to a critical value as the roughness increased and increased thereafter. A clear observation of turbulent kinetic energy and eddy viscosity showed that near-wall turbulence over the critical wall roughness increases the momentum transfer, and consequently the head developed by pump increases.