The volute is an essential element in the centrifugal machines. Improving its performance is an effective way to improve the total performance of the turbine. The purpose of this study is to replace the accelerating and guiding nozzle vanes by exploring different design possibilities on the cross-sectional area convergence of the volute, since a decreasing area is then associated with expansion in the subsonic regime. The work is extended to a mixed inflow turbine using the new volute cross sections under pulsating regimes for turbocharging. The numerical simulation results show larger accelerations (M 2 ' 0:95) and lesser losses in the case of sections with flatter area in the radial direction and without vaneless space between the volute and the rotor; but this combination has an effect on the exit absolute flow angle which is less uniform.

The development of the aerofoil-shaped turbomachine blades is of prime importance for achieving the appropriate deflection of a three dimensional flow through desired angles, to work at the same degree of incidence and thereby providing the required performances for the specific machine. The sensitivity of the rotor to incidence effects and tendency of the flow to separate from one or the other blade surface have given rise to considerations of the optimum incidence angle and cone angle for a mixed inflow turbine by a numerical investigation using the ANSYS-CFX code. In order to keep the rotor in the same casing some geometrical parameters have been hold constant and the Bezier polynomial is used to generate the new shape of the rotor blade when changing the cone angle magnitude.

Turbochargers are widely used in Diesel engines as a means of increasing the output power. Most of them are fitted with radial or mixed flow turbines. In applications where high boost pressure is required, radial turbines are replaced by mixed flow turbines which can achieve a maximum efficiency at a lower value of blade speed to isentropic expansion velocity ratio than the usual 0.7 (for radial turbines). This study, performed with the ANSYS-CFX software, presents a numerical performance prediction of a mixed flow turbine under inlet pulsating flow conditions. In addition, the influence of the pulse frequency is studied and the numerical results are compared with those of a one-dimensional model and experimental data.

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