3D-CFD-Study of Aerodynamic Losses in Compressor Impellers

Due to the increasing requirements for efficiency, the wide range of characteristics and the improved possibilities of modern development and production processes, compressors in turbochargers have become more individualized in order to adapt to the requirements of internal combustion engines. An understanding of the working mechanisms as well as an understanding of the way that losses occur in the flow allows a reduced development effort during the optimization process. This article presents three-dimensional (3D) Computational Fluid Dynamics (CFD) investigations of the loss mechanisms and quantitative calculations of individual losses. The 3D-CFD method used in this article will reduce the drawbacks of one-dimensional calculation as far as possible. For example, the twist of the blades is taken into account and the “discrete” method is used for loss calculation instead of the “average” method. The results show that at the same blade speed, the clearance loss reaches its maximum with a mass flow of 0.07 kg/s. Secondary losses are highest at low mass flows and reduce as the mass flow increases. However, at high mass flows the secondary loss has a slight increase because of the high velocity gradient. The velocity of the main fluid is high if the mass flow is large, which results in a high friction loss in the internal fluid as well as between the fluid and the casing. A 3D-consideration of impeller design makes the incidence loss change slightly with increased mass flow. The exit angle and instability of the main flow are decisive for the losses in the diffuser.