Pulsating flow in automotive turbocharger turbines makes it necessary to know performance characteristics in difficult to measure off-design conditions. Physically-based extrapolation models can be used to extrapolate towards unmeasured map regions. However, for model parameter fittings common maps have low numbers of measurement points per speedline available. Measurements with different variable geometry turbine (VGT) openings amplify the available data and help to characterize the turbine in a wider aerodynamic range. Nevertheless, physical models able to […]

The characterization of tip leakage flow plays an important role for one-dimesional loss modeling and design in radial turbine research. Tip leakage losses can be expressed as function of fluid momentum and mass flow passing through the tip gap. Friction-driven flow and contrariwise oriented pressure gradient-driven flow are highly coupled. However, these numbers are mostly unknown and dependent on tip gap geometry and turbine running condition. Based on a commonly used definition of a non-dimensional […]

Due to the power consumption restriction of the turbocharger compressor, common turbine maps are rather narrow. To extrapolate them, reliable physical submodels are needed that are valid for broad ranges. Plenty of research has been done referring to tip leakage losses in axial and traditional radial turbomachinery. However, less effort has been put into the tip leakage analysis of radial turbocharger turbines, whose characteristics including high rotational speed and geometry are rather different. Commonly developed […]

During automotive urban driving conditions and future homologation cycles, automotive radial turbines experience transient conditions, whereby the same operate at very high blade speed ratios and, thus, at very low power outputs. Under those conditions, the turbine power output might not be enough to feed the mechanical power needs of the compressor. Typical fast one-dimensional full engine simulations rely on steady-state performance maps to characterize the turbocharger. Due to the restricting compressor braking power, extreme […]