Experimental investigation and modeling of local resistance coefficient of reducing pipe using selective laser melting

Selective laser melting (SLM) technology is widely utilized in various industries such as aerospace, engineering machinery, and medical sectors due to its benefits in lightweight construction, rapid manufacturing cycles, and design adaptability. However, reducing pipes produced via SLM often exhibit significant and irregular surface roughness, posing challenges inaccurately predicting their local resistance coefficients using conventional hydrodynamic theories. Aiming at resolving this problem, the present study fabricates numerous Ti6Al4V reducing pipes with varying cone angles using SLM technology. The internal surface roughness distribution of these pipes is characterized and quantified. Through extensive experiments and numerical simulations, the local resistance coefficients of SLM reducing pipes are investigated, leading to the development of a novel prediction model. The study identifies several influencing factors on the local resistance coefficient, including cone angle, area ratio, Reynolds number, and surface roughness. It is observed that SLM reducing pipes encompass two distinct flow regions: the smooth region and the rough region, with the Reynolds numbers in the latter increasing with surface roughness. Moreover, a model incorporating critical values for both regions is established. The predicted local resistance coefficient model demonstrates a maximum error of only 10.96% when compared to experimental data, highlighting a substantial enhancement in prediction accuracy over traditional models.