Detailed velocity profiles in close-coupled elbowsMeasurements and computational fluid dynamics predictions (RP-1682)

This article presents a systematic study to measure detailed velocity profiles in close-coupled five-gore elbows having nominal diameters of 305mm (12 in) and turning radii r/D = 1.5, and to, likewise, predict the velocity profiles using computational fluid dynamics. The purpose of the testing was to study the physics of the flow in complex geometries and to provide data that can be used to verify the accuracy of computational fluid dynamics modeling predictions. The close-coupled elbow combinations comprised either a Z-shape or a U-shape configuration. In every instance the duct length separating the center-points of the elbows was systematically varied. Detailed velocity profile measurements were performed at one traverse plane located one duct diameter upstream of the first elbow and at one duct diameter downstream of the second elbow, and at various axial locations in the straight section between the close-coupled elbows. Velocity profiles results are compared to computational fluid dynamics Reynolds Stress Model and Large Eddy Simulation predictions for the effect of separation distance of the elbows in Z-shape duct configurations. Reynolds Stress Model turbulence modeling predicted the velocity trends correctly with a maximum error of 15%. However, Large Eddy Simulation modeling failed to predict the trend and the magnitude of the velocities, thus Large Eddy Simulation approach is not suitable for this type of flow.