A Need for Efficiency
A turbocharged diesel engine’s fuel consumption is directly influenced by the turbocharger efficiency through the engine’s pumping cycle work. The more efficient the turbomachinery, the lower the work done by the engine during the pumping cycle, resulting in better engine BSFC (Brake Specific Fuel Consumption). The overall turbocharger efficiency is the product of the compressor, turbine and rotor system efficiencies:
Overall Efficiency = Compressor Efficiency X Turbine Efficiency X Rotor System efficiency
Compressor efficiency therefore has a direct impact on engine BSFC and is one of the areas recently targeted by Cummins Turbo Technologies for improvements. In this article the application of TURBOdesign1 to improve the efficiency of a turbocharger centrifugal compressor wheel will be discussed.
The baseline impeller already had very high efficiency and previous attempts to improve its efficiency by using conventional (direct) design, based on iterative changes to blade angle had failed to produce a design with improved efficiency. The purpose of this project was to see whether its possible to improve this compressor’s efficiency by using inverse design code TURBOdesign1.
The initial plan was to design a straight filament geometry. However, the detailed study using TURBOdesign1 and 3D CFD confirmed that by using straight filament geometry it was very difficult to improve the performance of the compressor. However, the inversely designed impeller, which has 3D geometry, was found to show significant improvement in efficiency based on stage CFD, using a similar mesh to that shown below, which is using about 7 Million nodes.