The Experimental Study on the Aerodynamic Performance Improvement Using Retrofitted Augmented Diffusers in Centrifugal Stage

The centrifugal compressor stage is the device that delivers kinetic energy into work fluid, which then converts the kinetic energy into potential energy and finally collects the energized fluid. The components for implementing these three steps are the impeller, diffuser and volute, respectively. In addition, the Inlet Guide Vane (IGV) is the optional component that adjusts inlet flow angle and extends the stage surge margin. The evaluation of the centrifugal stage aerodynamic performance mainly includes two aspects, stage aerodynamic efficiency and operating range, from surge to choke. Designers can improve any one of three components, impeller, diffuser and volute, to raise stage performance. This paper introduces methods to obtain the enhanced stage aerodynamic performance by using augmented diffuser. The project started from the existing centrifugal compressor stage equipped with the traditional and matured vaneless diffuser and IGV. The impeller tip Mach Number is about 1.3. The authors design various types of augmented diffusers that can fit into the vaneless diffuser space by 1D meanline analysis and 3D CFD simulations. The co-relation between augmented diffuser and IGV is also investigated. This retrofitted centrifugal stage is taken as the test vehicle to conduct a series of tests which target stage aerodynamic performances for various augmented diffuser specimens. The summary of the test results indicates that there is an 8+% of an efficiency performance improvement through the augment diffuser only. Combining with the IGV, there is 16+% surge margin improvement. The efficiency is also improved when the flow is less than that at design condition. All results are discussed, and conclusions are made.