Initial Stage Sizing
The initial meridional shapes and main dimensions for the compressor stage were produced using 1D preliminary design software TURBOdesign Pre. Starting from the basic stage requirements of mass-flow rate, pressure ratio and rpm, the code provides the overall stage sizing and detailed component performance and characteristic across the operating range.
3D Impeller and Vaneless Diffuser Design
Using 3D Inverse Design software TURBOdesign1, the blade loading distribution was optimized in order to achieve the target pressure ratio at the design mass flow and obtain good compressor impeller efficiency.
The compressor needed good efficiency over a very wide operating range, and so a vaneless diffuser design was produced. Vaneless diffuser pinch width and length were optimized as part of the design process.
Designs produced were tested by means of commercial CFD codes. Designs were analyzed both at design point and the most challenging off-design points. The final design was also analyzed across the entire operating map, considering different compressor speed lines between 40% and 120% of the design rotational speed.
CFD analysis showed that the final design reached all target pressure ratios and mass flows, whilst meeting all target efficiences and exceeding the design point target efficiency (including the volute) by 2%. Finite Element Analysis (FEA) was carried out on the final design, showing an acceptable stress level in the optimized blade, which allowed simple aluminium alloy to be used by the customer for manufacturing of the blades. In addition, blade natural frequencies were assessed and showed significant margin to requirements.