Numerical Analysis of Turbulent Flow Developing in S-Shaped Diffuser.

Abstract

A numerical analysis of developing turbulent flow in a diffuser with S-shaped centerline at a Reynolds number of 4×104 has been carried out. The diffuser exit-to-inlet area ratio was 1.5, the inlet cross section was square, 40mm×40mm, and was expanded on both curved surfaces to an exitplane section of 40mm×60mm. The S-shaped curvature was formed from two 22.5 degree bends of 280mm mean radius of curvature. Straight ducts 0.3m and 2m long were attached to the inlet and outlet planes of the S-shaped diffuser, respectively. In the calculation, an algebraic Reynolds stress model was adopted for predicting anisotropic turbulence precisely, and a boundary-fitted coordinate system was introduced for coordinate transformation. Calculation results for mean velocity were compared with the experimental data. In addition, the difference in flow between the S-shaped diffuser and the S-shaped duct is presented with calculation results. Using by the present method, we found that the flow at the inlet shows a core flow located near the inner wall of the first bend, and a region of low velocity fluid which has accumulated at the exit of the diffuser was observed. It was also found that the secondary flow patter of the S-shaped diffuser was similar to that of the S-shaped duct in the first bend but differed from it in the second bend.