10th European Conference on Turbomachinery Fluid dynamics & Thermodynamics

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H.P. Dickmann - ABB Turbo Systems Ltd, Baden, Switzerland


A wide range of flow rates can only be covered by a family of compressors which are called trims. In the compressor map trims differ by a horizontal shift of the speed lines. Designs for lower flow rates are achieved by reducing the passage area. The goal is to maintain efficiency and pressure ratio of the base design as far as possible. In this study, an optimizing tool has been used to design the axisymmetric impeller shroud contour for each trim. Only the best efficiency point of the 100% speed line for each trim was optimized. Afterwards two complete speed lines were computed with the new geometry and analyzed. Whereas smaller trims typically show considerably lower efficiency levels, this optimization resulted in a relative efficiency loss of 0.94% only for an almost 20% smaller geometry combined with the same absolute tip clearance as the one of the base design. The pressure ratio of the best point of the base design could be maintained for all trims.

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