This paper presents a detailed loss analysis of a centrifugal compressor stage with a vaned diffuser for application in a heavy duty engine turbocharger. The analysis is carried out in order to investigate the loss distribution in the stage. To quantify the impact of different loss types and locations, a detailed validated steady-state 3D CFD solution is employed. The local entropy production rate is calculated for two operating points (full load and part load), which are most relevant to the real world operation of the compressor in a truck application. Two methods are suggested as the procedure for the division of the whole fluid volume into sub-volumes, because this is key for the resulting loss distribution.

The primary loss generating mechanisms are shown at main operating conditions to reveal the regions of improvement. A detailed grid study was conducted to enable the calculation of the entropy ratio. It was possible to capture around 78% (partial load) and 70% (full load) of the entropy production with a mesh with circa 100 million elements. Around half of the losses were due to the boundary layer friction, followed by losses associated with a boundary layer separation resulting from the back-flow at the shroud contour close to the impeller exit and back disk friction accounted for with 6–7% of the stage’s losses.

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