Physical Model of a Twin-scroll Turbine with Unsteady Flow 2015-01-1718
The paper describes a way to a 1-D central streamline model of a radial turbine flow, suitable for twin-scroll description and based on approximation of real physics of flow mixing and energy transformation. The original 1-D model of a single scroll turbine, described earlier in numerous SAE papers, has been amended by twin-scroll nozzles (both vaneless or with blade cascades) and mixing of individual partitions of flows upstream of additional vaneless nozzle and an impeller. This model is transferable to 1-D unsteady simulations as it is (i.e., using quasi-steady approach) or using 1-D unsteady solvers. It has suitable features even for more detailed description of turbine flows and energy transformation. The first results of pulse influence on turbine maps delivered expected results consisting of complicated interaction between individual losses.
The model itself is not fully predictive, using experimentally or in CFD found loss coefficients, but it is suitable for extrapolation of experience from similar systems before detailed CFD simulation or experiments are done. The new model can be used especially transferring turbine features found during mapping back to the design stage at a turbocharger manufacturer.
The features of twin scroll turbines call for appropriate optimization of turbines for high pulsation factor, as they are currently used for twin-scroll four cylinder engine turbochargers (two cylinders with 360° distance between pulses). The results of turbine matching should be used as a feed-back for turbine design.