On Mixed Flow Turbines for Automotive Turbocharger Applications

Abstract

Due to increased demands for improved fuel economy of passenger cars, low-end and part-load performance is of key importance for the design of automotive turbocharger turbines. In an automotive drive cycle, a turbine which can extract more energy at high pressure ratios and lower rotational speeds is desirable. In the literature it is typically found that radial turbines provide peak efficiency at speed ratios of 0.7, but at high pressure ratios and low rotational speeds the blade speed ratio will be low and the rotor will experience high values of positive incidence at the inlet. Based on fundamental considerations, it is shown that mixed flow turbines offer substantial advantages for such applications. Moreover, to prove these considerations an experimental assessment of mixed flow turbine efficiency and optimal blade speed ratio is presented. This has been achieved using a new semi-unsteady measurement approach. Finally, evidence of the benefits of mixed flow turbine behaviour in engine operation is given. Regarding turbocharged engine simulation, the benefit of wide-ranging turbine map measurement data as well as the need for reasonable turbine map extrapolation is illustrated.

A numerical study of automotive turbocharger mixed flow turbine inlet geometry for off design performance

“…One suggested solution to these issues is a mixed flow turbine [4][5]. A mixed flow turbine differs from a radial turbine as its inlet is not at a constant radius but rather is inclined at an angle, commonly referred to as the cone angle, as shown in Figure 2.…”

Influence of the volute cross-sectional shape on mixed inflow turbine performances

“…However, the filling time through the inter-blade passages within the rotor is very small, and in this situation, the quasi-steady model is specially used. 14 The characteristic results obtained from the unsteady three-dimensional simulation involve the determination of the different values of mass flow rate and pressure ratio in each boundary at the inlet and at the outlet of Figure 11. The instantaneous total to static pressure ratio at 50% speed for two frequencies of 40 and 60 Hz are plotted with solid (black) and dash (red), respectively.…”

The introduction of a tilted volute design for operation with a mixed flow turbine for turbocharger applications

“…As a result, mixed flow turbines effectively operate like radial turbines with swept back blades. This is achieved through the introduction of a blade cone angle and the presence of a blade camber angle at the LE, this effect is reported in detail by [3] and [4].…”