In this work, a new two-dimensional method is presented for turbine volute design. In this method, the continuity equation, energy equation, free vortex equation, and streamline equation are employed to solve the velocity field and to generate the volute profile. The physical model and mathematic solution to the governing equations are described in detail. A new volute for a turbocharger turbine is generated using this method and compared with the original, well-designed baseline volute. Different turbine operating conditions, including equal and unequal admission cases, were studied by CFD to compare turbine aerodynamic performance using the new and baseline volutes. The simulation results show that the efficiency of the new volute is about 0.4%–0.6% higher than the baseline under equal admission conditions. It is found that the improvement in turbine performance is mainly due to the more reasonable A/R distribution, which reduces the losses in the turbine. This work demonstrates that the proposed new method provides an effective way for radial turbine volute design, and can quickly create high performance volutes.

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Secondary flows had been found in radial turbine volutes in the past, but the flow mechanisms governing their existence are far from clear. This paper describes an analytic and numerical work on the mechanism of the secondary flows, and the effects of volute shape, A/R distribution, and turbine speed on the development and associated losses of the secondary flows in the turbine volutes. The results show that the centrifugal and viscous forces acting on the wall boundary-layer, as well as the diffusion of radial flow in volute’s cross-sections, are the main generating mechanism of secondary flows, but they are worked against by volute discharging. Compared with the rectangular and trapezoidal shape volutes, the circular volute generates stronger secondary flows, resulting in no hydrodynamic benefit over the other two volutes. By using the dissipation function to separate the secondary flow loss from the total loss in the three volutes, it shows for the first time that although the loss from secondary flows alone is small, the flows can push the main flows toward volute side walls thereby increase wall friction loss. Three twin-entry volutes with different aspect ratios of their cross-sections are also studied. The offset of the cross-section center to volute exit affects volute discharging and the aspect ratio impacts on the radial flow in sidewall boundary layers, they therefore influence the secondary flows in the volutes. The slope of A/R curves is found to correlate well to the strength of the secondary flows in the volutes, and the reason behind is explained. Turbine speed’s influence on the secondary flows is largely through flow compressibility, and if the speed change reduces turbine inlet Mach number, it will increase discharge flow angle at the volute exit, and so too the strength of the secondary flows, but the changes will be small.

Nozzleless housings for turbocharger turbines accelerate and guide flow into downstream rotors. Their design affects the aerodynamic performance and reliability of the turbines. Due to the three-dimensional nature of the volute of the housings, turbine housing volute design is largely based on extended 1D theories and trial-and-error method. In this paper, a detailed description of an extended two-dimensional theory for volute design is given, including its numerical implementation. The method is then applied to design a twin-entry turbine housing for a turbocharger turbine under both equal and unequal admissions, to replace a highly optimized, manually designed housing. The results show that the new volute achieves the same turbine aerodynamic performance as the manually optimized volute with greatly reduced design time, and it also generates more uniform rotor inlet condition with lower pressure excitation force. A breakdown of the stage loss shows that the loss in the new volute housing is larger than that in the manual housing due to its smaller overall dimensions, but the losses inside rotor and downstream diffuser are both reduced due to the more uniform volute exit flow. A discussion on the secondary flow in the two volutes is carried out to show how the volute geometry, through influencing the radial discharge from the volute exit, affects this flow. A further discussion on the flow angle jump around the tongue is placed at the end of the paper to show the mechanism of this jump, how to control it in volute design, and to offer a way forward to improve the volute design method.

In order to meet the higher design requirements of radial turbines, it is necessary to clearly understand the impact of different design parameters on turbine performance. The A/R distribution is one of the most important design parameters for the radial turbine volute, but there are few studies on it. To clarify the effect of A/R distribution on turbine efficiency and blade excitation force, a detailed comparative study is carried out. An experimentally validated numerical method is used, and steady and unsteady CFD simulations are conducted in this study. The results show that the volute A/R distribution has a significant effect on the turbine efficiency, while a linear distribution can provide a more uniform inlet condition and thus improve the rotor efficiency. The flow parameters fluctuated significantly at the volute tongue. Although the efficiency is not sensitive to this fluctuation, it directly affects the excitation force on the rotor blades. The volute with S-shaped A/R distribution produces the smallest excitation force due to the smallest fluctuation. Two new A/R distributions are presented which combine the advantages of linear and S-shaped or convex A/R distributions with high efficiency and low excitation force. It is suggested that the A/R should be close to the linear distribution and decreases rapidly before the tongue.