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In the paper the results of an experimental campaign regarding the steady characterization of a turbocharger waste-gated turbine (IHI-RHF3) for gasoline engine application are presented. The turbine behavior is analyzed in a specialized test rig operating at the University of Genoa, under different openings of the waste-gate valve. The test facility allows to measure inlet and outlet static pressures, mass flow rate and turbocharger rotational speed. The above data constitute the basis for the tuning and validation of a numerical procedure, recently developed at the University of Naples, following a 1D approach (1D turbine model - 1DTM). The model geometrically schematizes the entire turbine based on few linear and angular dimensions directly measured on the hardware. The 1D steady flow equations are then solved within the stationary and rotating channels constituting the device. All the main flow losses are properly taken into account in the model.

Downsizing is widely considered one of the main path to reduce the fuel consumption of spark ignition internal combustion engines. As known, despite the reduced size, the required torque and power targets can be attained thanks to an adequate boost level provided by a turbocharger. However, some drawbacks usually arise when the engine operates at full load and low speeds. In fact, in the above conditions, the boost pressure and the engine performance is limited since the compressor experiences close-to-surge operation. This occurrence is even greater in case of extremely downsized engines with a reduced number of cylinders and a small intake circuit volume, where the compressor works under strongly unsteady flow conditions and its instantaneous operating point most likely overcomes the steady surge margin. In the paper, both experimental and numerical approaches are followed to describe the unsteady behavior of a small in-series turbocharger compressor.