Experimental and Numerical Assessment of the Impact of an Integrated Active Pre-Swirl Generator on Turbocharger Compressor Performance and Operating Range

The implementation of increasingly stringent emissions and efficiency targets has seen engine downsizing and other complementary technologies increase in prevalence throughout the automotive sector. In order to facilitate ongoing improvements associated with the use of these strategies, delivering enhancements to the performance and stability of the turbocharger compressor when operating at low mass flow rates is of paramount importance. In spite of this, a few concepts (either active or passive) targeting such aims have successfully transitioned into use in automotive turbochargers, due primarily to the requirement for a very wide compressor-operating range. In order to overcome the operational limitations associated with existing pre-swirl generation devices such as inlet guide vanes, this study developed a concept comprising of an electrically driven axial fan mounted upstream of a standard automotive turbocharger centrifugal compressor. Rather than targeting a direct contribution to compressor boost pressure, the fan was designed to act as a variable pre-swirl generation device capable of being operated completely independently of the centrifugal impeller. It was envisioned that this architecture would allow efficient generation of the large pre-swirl angles needed for compressor surge margin extension and efficiency enhancement at low mass flow rate-operating points, while also facilitating the delivery of zero pre-swirl at higher mass flow rates to ensure no detrimental impact on performance at the rated power point of the engine. Having progressed through 1-D and 3-D aerodynamic modelling phases to understand the potential of the system, detailed component design and hardware manufacture were completed to enable an extensive experimental test campaign to be conducted. The experimental results were scrutinized to validate the numerical findings and to test the surge margin extension potential of the device. Compressor efficiency improvements of up to 3.0% pts were witnessed at the target-operating conditions.