Increasing interest in improving the efficiency of the turbo-fan engine results in a large low pressure compressor and small high pressure core. The consequence of the increment in radial offset is that the importance of the transition duct is growing. Shortening this transition duct length can effectively reduce the weight of the engine. However, it conflicts with the need to avoid flow separation within the duct. Further, radial struts are also present in duct passage for support. In present work, numerical investigations were performed on an annular S-duct with bypass suitable for connecting the compressor spools of a small turbofan engine. The length of S-duct was reduced by 6%, 12%, and 18% from the original S-duct length. The wall contour was selected based on the optimum value of the total pressure loss coefficient for the particular length. It was found that the loss coefficient is a weak function of duct length as long as the flow is attached. Further, the effect of the radial strut on the selected contour for two different lengths was studied. The increase in loss for 100% and 88% length in the presence of all struts was 17% and 27%.

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