Abstract: Thick struts which intersect an S-shaped transition duct in an axial compression system tend to cause blockage in the flow passage and significantly influence the performance of the duct. As there are no design rules available for them, design of a transition duct with struts involves three dimensional numerical optimization, which is rather complicated. To simplify the issue in the design phase, an axisymmetric equivalent method which can reduce the problem to two dimensional problem is established. First, the theoretical concepts of axisymmetric equivalent method are presented based on the influence of struts on the pressure field in the duct. Then, the main features of the flow field in the equivalent duct and the strutted duct are compared through numerical calculation. It is shown that the endwall pressure distribution of the two ducts agrees well, and that they exhibit similar loss variation features, which both indicate that the equivalent duct is capable of capturing the major influence of struts. Finally, the equivalent method is applied to the optimization of a baseline strutted duct with separation in the strut-hub area due to high local diffusion. The optimized duct is found to have removed the separation completely, and decreased the loss by 41.6%.

Key words: S-shape transition duct, strut, axisymmetric equivalent, fan/compressor