Laser doppler measurements of turbulent swirling flows in a circular tube with a sudden expansion followed by a sudden contraction

摘要

Two component Laser Doppler Velocimetry measurements have been made in a turbulent flow field in an axisymmetric confined sudden expansion, followed by a contraction. Measurements were made using different inlet swirl numbers and Reynolds numbers. One flow field with reduced distance between the expansion and the contraction was also studied. The investigated geometry can be seen as a simplified gas turbine combustor, where the swirl is introduced to increase the mixing rate and stabilize the flame. When the swirl is introduced, the turbulent energy increases, and when the swirl number reaches a value between 0.33 and 0.43 a central recirculation zone occurs, which increases with increasing swirl number. For higher swirl numbers the central recirculation zone has a hollow core shape. To characterize the influence of the periodic disturbances that are associated with swirling flows, an integration of an estimated power spectrum around the frequency of the periodic disturbances was made. It was found that as much as 50% of the turbulent kinetic energy is associated with the periodic disturbances. The measurements include mean velocities and Reynolds stresses, which provide a data base suitable for model validation. 36 refs, 47 figs, 7 tabs