Modeling the hydraulic impact of SLM-induced wall roughness in TA15 alloy via a user-defined function approach

Selective laser melting (SLM) provides significant design freedom for hydraulic components, yet the inherent wall roughness from powder adhesion degrades fluid flow performance, an effect standard CFD models struggle to capture. This study presents a systematic framework to address this challenge by integrating experimental surface data into fluid dynamics simulations. A user-defined function (UDF) was developed in Fluent to translate experimentally measured 3D surface topographies of as-built TA15 titanium alloy into a non-uniform, equivalent sand-grain roughness model. This approach specifically accounts for stochastic, localized powder agglomerates. The feasibility of the UDF methodology was first verified against a benchmark case, confirming its capability to represent localized flow disturbances. When applied to a complex, self-supporting diamond-shaped channel, this data-driven model predicted a 55 Pa pressure loss increase (a 4.5% rise) and significantly intensified near-wall turbulence compared to a smooth-wall assumption. This work provides a methodologically verified and practical framework for more accurately predicting the hydraulic performance of as-built SLM components. It offers a critical tool for designers to anticipate and mitigate the impacts of surface roughness in next-generation, high-efficiency lightweight hydraulic systems.