Advanced Numerical/Experimental Methods for the Analysis of a Waste-Gated Turbocharger Turbine

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. A preliminary tuning is carried out based on the characteristic map measured for a completely closed waste-gate valve. A 1D schematization of the experimental test rig is implemented within the commercial GT-Power™ software, including the turbine, the waste-gate and the upstream and downstream circuits. In particular, the turbine model itself consists of a sequence of pipes that schematize each component of the device (inlet/outlet ducts, volute and wheel). The pipes dimensions are automatically provided by the geometrical module of the 1DTM. In the turbine schematization, the “wheel-map”, estimated by means of the above mentioned 1DTM, is utilized. The latter does not take into account phenomena and losses occurring in the volute and in the intake/outlet ducts, as well. A refined modeling of the waste-gate system reveals to be necessary to correctly reproduce the swallowing capacity of the by-pass port. The waste-gate model is tuned against the experimental findings for a completely closed turbine wheel and various settings of the by-pass port. Finally, once the 1D models of the turbine and of the waste-gate system are independently tuned, their behavior under parallel flow is analyzed. The proposed numerical and experimental results demonstrate the mutual interaction of the two components. In addition, it is put into evidence that turbine and waste-gate circuit cannot be considered as two systems working in parallel under the same pressure ratio, as usually assumed in 1D codes.