AN EXPERIMENTAL AND NUMERICAL STUDY OF A 90-DEGREES BIFURCATION

The how held of a 90 degrees square duct bifurcation was examined both experimentally and numerically for a Reynolds number of 1200 and equa l branch flow rates. Velocity measurements were carried out with a one -component LDV, recording, besides the time mean streamwise velocity c omponent, its time variation due to vortex shedding which took place i n the extension of the main duct, as well as secondary flow velocities in the 90 degrees branch. Flow visualization provided additional info rmation about the three-dimensional character of the how field by reco rding the paths of neutrally buoyant solid particles. The experimental data were compared with the results of a numerical method, constituti ng an extension of the well-known SOLA method to a 3-D generalized coo rdinate system, presented here for the first time. These comparisons w ere very successful in the vertical branch but less satisfactory in th e horizontal branch where unsteadiness was very strong. The characteri stic frequency of the velocity fluctuations in the detached shear laye r of the horizontal branch was very well predicted but the velocity am plitudes were underestimated. The predicted secondary flow in the vert ical branch was compared well with the experimental data presenting ma ximum values close to the inlet mean velocity.