Designing a Refrigeration Compressor Stage

The client is a global leader in providing customized, high performing, highly engineered cooling systems. They asked ADT to design a compressor stage of a cooling system including an impeller with splitter blades, a vaneless diffuser and a volute for a target pressure and an efficiency level of about 3 points above their existing designs. Other constraints in the design were the maximum allowable stress level and vibration constraints.

A preliminary design using ADT’s 1D sizing code, TURBOdesign Pre, was performed in order to create an approximate meridional shape and other global geometrical parameters for each component. TURBOdesign1, the 3D inverse design code, was used to design the impeller blade. Finally, TURBOdesign Volute was used for the volute design.

Several design iterations were performed, followed by CFD analyses of the flow in the compressor stage at design and off-design conditions. By fine-tuning the inverse design parameters including the blade loading of the full blade and splitter blade, span wise work distribution and work ratio of the full and splitter blades as well as stacking condition, it was possible to reach a highly optimised configuration where the target efficiency and all other design constraints were fully satisfied.

The trimming function of TURBOdesign1 was then used to create the impeller geometries corresponding to different target flow rates and pressure ratios.

Figure 1 shows the flow streamlines in the compressor stage, while the performance characteristics of the compressor stage with the full impeller and meridional trimmed impellers are shown in Figure. 2.