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Variable geometry twin-entry turbine has advantages in fuel economy, low-end torque, emission and turbo-engine matching of internal combustion engine. The reliability of performance prediction method for nozzled twin-entry turbine is heavily dependent on the understanding of flow mechanism of the turbine which is always confronted by time-dependent unequal admissions. This paper establishes a new meanline model of a nozzled twin-entry turbine based on the internal flow features. Firstly, flow mechanism of the twin-entry turbine with a vaned nozzle under different admissions is investigated via an experimentally validated CFD method. Results clearly demonstrate that the flow distortion in spanwise direction caused by unequal admissions notably influences the turbine efficiency discrepancy between symmetric unequal admissions, especially the two partial admissions. The evolution of flow distortion in the nozzle passage is the key to the performance discrepancy, which is impossible to be considered by a conventional performance model of a nozzled twin-entry turbine. Inspired by this, a newly-designed meanline model, named ‘parallel nozzle’ is proposed. Specifically, a nozzle passage is divided into two parallel sub-passages in spanwise direction to consider the flow distortion in nozzle passage. The model is validated against the detailed CFD results in terms of both overall performance and detailed flow parameters over different admissions. Results prove that turbine performance and flow parameters are well predicted by the model. Specifically, the influence of admissions on nozzled twin-entry turbine performance and flow parameters can be predicted by the method in satisfying accuracy.

Pulsating turbocharging system with a dual-entry turbine is always applied for the utilization of pulsating energy and improvement of low-speed torque for the internal combustion engine. With the enhancement of pulsating energy via the pulsating turbocharging system and dual-entry turbine, the interaction between exhaust manifolds and dual-entry turbine cannot be disregarded by either side when confronted by pulsating inflows. This paper proposes a gasdynamic model of double-entry turbine coupling with exhaust manifolds to examine the interaction effect between turbine and exhaust manifolds. This gasdynamic model can predict the propagation of pressure and mass flow rate from exhaust manifolds to the double-entry turbine as well as transient turbine performance. Predictions of this gasdynamic model are validated against detailed 3-D simulation and show good consistency with 3-D results. The performance and energy distribution of the double-entry turbine coupled to exhaust manifolds under various pulsating conditions are thoroughly discussed via this reduced-order model. Results show that with increasing frequency or amplitude of pulsating inflows imposed on inlets of the exhaust manifolds, the performance of the entire system deviates from the quasi-steady hypothesis, particularly the swallowing capacity. This phenomenon indicates that the matched operating point between the turbine and engine deviates from the quasi-steady conditions. In addition, exhaust manifolds geometries have a notable impact on turbine performance and energy distributions in exhaust systems. It is found that with an increase in the volume or length of the exhaust manifolds, the pulse at the turbine inlet is amplified, and available energy at the turbine inlet is increased, even though the inlet conditions of exhaust manifolds remain unchanged. This study may provide a guiding effect for the optimization of the turbo-engine matching process and the development of high-performance turbocharged engines.