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In this paper, a novel one-dimensional matching method of an asymmetric twin-scroll turbine (ATST) with a small scroll bypass wastegate is initially presented for energy improvement. The developed method presents further insights into efficiency prediction of the ATST and the small scroll exhaust bypass in the matching process of model characterization. The efficiency of the small and large scroll turbines was approximately assessed with two times flow parameters of the small and large scroll turbines, respectively, as well as according to turbine efficiency prediction curves. Subsequently, given the matching results of a 9-L engine, a targeted ATST was developed; its effectiveness was verified by computational fluid dynamics (CFD) and the performance tests of a turbine and an engine. As revealed from the results, the prediction efficiency of the ATST well complies with that of the numerical calculation and performance tests of turbines and engines. Compared with the common large scroll exhaust bypass wastegate, the small one exhibits better engine performance and can save nearly 0.5–1.5% fuel consumption at middle and high engine speeds. Moreover, the reasons of which were explored for better understanding of the mechanism accordingly.

Rotating stall contributes to global oscillation vibration problems, accompanied by noise and possible turbomachinery damage. This study with special emphasis on the vaned diffuser investigates the unsteady pressure interaction with the stall within the pump. A low specific speed centrifugal pump (n s = 69), fitted with a vaned diffuser is modeled and studied. The model pump performance curve shows the characteristic positive slope at 30% of the best efficiency point flow rate; 1.0 Φ Ν which is attributed to the stall phenomena.A finite volume method is employed with unsteady computations initialized utilizing shear stress transport k-ω before proceeding with DDES. Pressure fluctuation and velocity magnitude normalized values are used to investigate the evolution of stall cell generation. The root mean square (RMS) values and normalized pressure (Cp) values are elicited to gain insight into pressure pulsation within the flow domain. The distinguished "starfish" shape is observed for monitor points md1 to md20, with the RMS trend decreasing with increasing flow rate from the pump shut off. Although in the vaned diffuser flow channel, an increase in pressure fluctuation along the flow channel toward the trailing edge is observed, the vaned diffuser channel shows a similar trend. The stall cell propagates at a speed of Ω RS = 0.078 at 0.2 Φ Ν , while at 0.1 Φ Ν propagates at a speed of Ω RS = 0.087; the stall speed tends to increase approaching pump shut off. Three distinguishable stall channels are observed from the flow structure for a five vaned diffuser; entering the stall, stalled, and stall recovery stages, within the flow channels.