Flow characteristics inside a diffuser of complex shape

Abstract

An experimental study was made of an incompressible flow through a model S-shaped semicircular to circular transition diffusing duct. The transition diffuser has a length—exit diameter ratio of 3 and a duct offset ratio of 0.3. The operating Reynolds number based on hydraulic diameter and bulk velocity is 40 000. The refraction index matching technique and laser Doppler velocimetry were used for velocity measurements. The measurements indicate that flow distortion persists at the outlet and the separation of the boundary layers is incipient. Semicircular to circular transition duct flow was studied in order to document the transition duct flow field and to provide detailed duct flow data for comparison with numerical code prediction. Experimental results also suggest that details of the near-wall flow incipient separation region and the distortion of the flow in the second half of the diffuser are likely to provide a severe test for various computational methods and turbulence models.