Abstract
A hydrogen turbo hybrid power system has the significant advantages of zero carbon emissions, high efficiency and high reliability. The need to increase the power density of hydrogen turbo hybrid power systems and improve the adaptability of turbines over a wide range of expansion ratios has encouraged the study of transonic turbines. This paper is aimed at analyzing the flow characteristics and developing the loss models of a transonic turbine. The main losses for a subsonic radial turbine are usually divided into four parts: incidence loss, passage loss, tip clearance loss and trailing edge loss. Nevertheless, when the expansion ratio of a turbine is greater than about 2.6, the turbine will choke and work in transonic conditions. A shock wave will occur at the trailing edge, which will cause a lot of losses. The loss caused by the shock wave at the trailing edge is ignored by previous loss models. This paper develops a shock wave-induced loss model to predict the performance in transonic conditions more accurately. With the developed shock wave-induced loss model, the predicted efficiency deviation in transonic conditions decreases from 10% to 3.5% maximally.
Highlights
To meet carbon peak and carbon neutrality requirements, the need for efficient and environmentally friendly transportation equipment has been increasing steadily
Under the condition of a certain expansion ratio, the oblique shock wave on the blade pressure surface occurs at the Mach reflection on the blade suction surface, and an obvious shock wave surface is formed near the outlet of the blade passage
The shock wave-induced loss is caused by the shock wave near the trailing edge in transonic conditions, which contains the loss caused by the shock wave itself and the loss caused by the interaction of shock wave and the boundary layer, the leakage flow and the others
Summary
To meet carbon peak and carbon neutrality requirements, the need for efficient and environmentally friendly transportation equipment has been increasing steadily. To increase the power density of the hydrogen turbo hybrid power system and improve its adaptability to vehicle operating conditions, the turbine needs to operate over a wide range of expansion ratios, from subsonic conditions to transonic conditions. Computational fluid dynamics (CFD) can replace experiments to obtain turbine performance, turbomachinery designers still tend to use empirical loss models for turbomachinery design and off-design performance analysis, because empirical loss models can provide design results accurately and quickly [5–7]. These loss models reflect the irreversibility of turbomachinery and cause a decrease in efficiency as a result [8].
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