Critical Appraisal of Integrated Computational Fluid Dynamics/Surface Roughness Models for Additive Manufactured Swirl Burners

Abstract

Additive manufacturing (AM) technology can create complex parts that are otherwise impractical to manufacture by traditional methods. However, the process often results in rough and irregular surfaces that can affect performance. In this study, computational fluid dynamics (CFD) is considered as a tool to optimize component design for use in applications such as a gas turbine. However, modeling the interactions between turbulent flows and AM-generated wall roughness affect the predictive capability of numerical models due to difficulty in thoroughly characterizing rough wall texture. To progress toward addressing this issue, this study aims to appraise two common wall roughness approaches within the Reynolds-averaged Navier–Stokes (RANS) framework: the modified “law-of-the-wall” and roughness-resolving approaches. The modified law-of-the-wall is based on the correlation that converts the measured surface roughness parameters to the equivalent sand-grain roughness height. The second approach involves the resolution of the roughness elements within the computational grid. The simulations were compared against the velocity data published for the burner with AM swirl nozzle inserts of different surface finishes. At this stage of development, the realizable k–ɛ turbulence model was selected for all the CFD simulations. The results show that the roughness-resolving approach was better suited than the modified law-of-the-wall correlation, demonstrating good agreement with the experimental velocity data, predicting the velocity shift to the center. The model also revealed the shortened recirculation zone with increasing surface roughness, which is important in predicting flame stability and emissions performance to be studied subsequently.