This paper is a numerical simulation that was made in the three-dimensional flow, carried out in a modified centrifugal compressor, having vaned diffuser stage, used as an auto-motive turbo charger. Moreover, the performance of the centrifugal compressor was dependent on the proper matching between compressor impeller and vaned diffuser, influencing significantly surge and the efficiency of centrifugal compressor stages. In addition, a modified compressor impeller, coupled with vane and vaneless diffuser, has been found to have similar internal flow patterns for both the vaneless and vaned diffuser design. The vaned diffuser effect has been paid particular attention in terms of better analysis where the diffuser was designed for high sub-sonic inlet conditions. Another aim of this research was to study and simulate the effect of vaned diffuser on the performance of a centrifugal compressor. The simulation was undertaken by using a commercial software, the so-called ANSYS CFX, to predict numerically the performance in terms of pressure ratio, poly tropic efficiency and mass flow rate for the centrifugal compressor stage. The results were generated from CFD and were analyzed for better understanding of the fluid flow through centrifugal compressor stage. Conclusively, it was observed that the effect of the vaned diffuser is to convert the kinetic energy into a high static pressure after analyzing the results of the simulation.

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These days the turbocharging system is assuming an essential part in enhancing car engines performance and diminishing fuel utilization and the fumes emanations, in spark-ignition and compression ignition engines. The performance of a radial turbine for the turbocharger device is heavily affected by the flow dynamics in a radial impeller. Furthermore, modification and improvement of a radial turbine impeller is a challenging task for turbomachinery engineers. Hence, this study aimed to further computational fluid dynamic analyses of a radial turbine stage performance .The design characteristics of a radial turbine stage,  was used to simulate the flow by using independent packages of ANSYS CFX. The comparative study of a three dimensional flow simulation will give a more reasonable results of the turbine stage flow behavior and computational fluid dynamic simulation can give a more detailed result and reveal unexpected flow behavior like separation and vortexes.The results showed that the fluid flow dynamics within a turbine stage has indicated a noticeable performance characteristics. Obviously, it was observed that the pressure ratio and volume flow rate and efficiency were predicted numerically. Overall  numerical results obtained from computational fluid dynamic simulations could produce a highly reliable for estimation on the performance a radial turbine of turbocharger.

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