Multi-Objective Optimization of a Highly Loaded Radial Compressor

A transonic centrifugal compressor was aerodynamically optimized at the Institute of Jet Propulsion and Turbomachinery, headed by JARA-ENERGY member Prof. Peter Jeschke, by means of a numerical optimization process. The main applications of these compressors are among others turbochargers of ships, power stations, diesel locomotives, or small gas turbines, small jet engines and auxiliary power units.

The objectives were to increase the isentropic efficiency and to reduce the acoustic signature by decreasing the amplitude of pre shock pressure waves at the inlet of the compressor. The optimization was performed at three operating points at full speed line in order to maintain the operating range. At the design point, the specific work input was kept equal. The baseline impeller was designed by using ruled surfaces due to requirements for flank milling. To investigate the benefits of arbitrary blade surfaces, the restrictions of ruled surfaces were abolished and fully 3D blade profiles allowed. In total therefore, 45 parameters were varied during the optimization.

The combined geometric and aerodynamic analysis reveals that a forward swept leading edge and a concave suction side at the tip of the leading edge are effective design features for reducing the shock strength. Beyond that the blade shape of the optimized compressor creates a favorable impeller outlet flow, which is the main reason why the performance of the vaneless diffuser improves. In total a gain of 1.4 percentage points in efficiency, evaluated by CFD at the exit plane of the vaneless diffuser, is achieved. This benefit has to be proven by experiments. The measurements will be conducted of optimized design in 2017/2018 on the centrifugal compressor test rig at the Institute of Jet Propulsion and Turbomachinery.