Potential of flow pre-whirl at the compressor inlet of automotive engine turbochargers to enlarge surge margin and overcome packaging limitations

Due to the packaging constraints to which turbocharged engines are submitted in passenger cars, the inlet duct of the centrifugal compressor often requires a 90° bend. The compressor inlet perpendicular to its axis disturbs the flow and reduces the compressor performance. This paper presents an interesting solution based on a specifically designed inlet swirl-generator device (SGD) that palliates these negative effects. In addition, the SGD can be used to extend the surge margin of the compressor if the position of the SGD blades is modified in function of the reciprocating engine operation conditions. The paper describes how the swirl level and the pressure losses generated by the device have been characterized in a continuous flow test rig. After this the SGD plus a centrifugal compressor from a turbocharger unit have been tested in a specific turbocharger test bench. The results obtained show the influence of the SGD blades position on the compressor performance. In order to better understand the influence of the SGD on the turbocharger behaviour, the flow velocity triangles near the inducer have been reconstructed using an approach based on CFD calculations.