An experimental and numerical study of a 90° bifurcation

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Abstract
The flow field of a 90° square duct bifurcation was examined both experimentally and numerically for a Reynolds number of 1200 and equal branch flow rates. Velocity measurements were carried out with a one-component LDV, recording, besides the time mean streamwise velocity component, its time variation due to vortex shedding which took place in the extension of the main duct, as well as secondary flow velocities in the 90° branch. Flow visualization provided additional information about the three-dimensional character of the flow field by recording the paths of neutrally buoyant solid particles. The experimental data were compared with the results of a numerical method, constituting an extension of the well-known SOLA method to a 3-D generalized coordinate system, presented here for the first time. These comparisons were very successful in the vertical branch but less satisfactory in the horizontal branch where unsteadiness was very strong. The characteristic frequency of the velocity fluctuations in the detached shear layer of the horizontal branch was very well predicted but the velocity amplitudes were underestimated. The predicted secondary flow in the vertical branch was compared well with the experimental data presenting maximum values close to the inlet mean velocity.