Aerodynamic Design of Small Chiller Compressor for Domestic CHP Applications

The customer, one of the leading manufacturers of high speed rotating machines, asked ADT to carry out the complete aerodynamic design of a brand new centrifugal chiller compressor stage using the inverse design approach available through the TURBOdesign Suite software. Performance targets (Pressure Ratios and Efficiencies) and operating points were set by the customer before the start of the project. Tight requirements on off-design and mechanical performance and the overall size of the stage were also set by the customer.

INITIAL STAGE SIZING

The initial meridional shapes and main dimensions for the compressor stage were produced by means of the 1-Dimensional sizing software TURBOdesign Pre. Real gas effects are modelled directly in TURBOdesign Pre, with gas property data included via .rgp files produced using NIST REFPROP data.

 3D IMPELLER AND VANELESS DIFFUSER DESIGN

By using the 3D blade 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 requires good efficiency over a very wide operating range, and so a vaneless diffuser design was produced. Vaneless diffuser pinch width and length were optimised as part of the design process. 

Designs produced were tested by means of commercial CFD codes. Designs were analysed both at design point and the most challenging off-design points. The final design has also been analysed across the entire operating map, considering different compressor speed lines between 40% and 120% of the design rotational speed.

CFD analysis shows that the final design is reaching all target Pressure Ratios and mass flows, whilst meeting all target efficiencies and exceeding the design point target efficiency (including the Volute) by 2%.