Metamodel-Assisted Multidisciplinary Design Optimization of Casing Treatment for Centrifugal Compressor

This work describes my activity carried out within the Von Karman Institute in the Department of Turbomachinery and Propulsion on the Metamodel-Assisted Multidisciplinary Optimization applied to the Ported Shroud Centrifugal Compressor inside a Turbocharger in which a Cost Model will be added to the optimizer. The project is born from a collaboration between VKI and General Motors and we want to obtain a design of a ported shroud compressor that presents a recirculation channel with an innovative U-Bend shape. The current manufacturing techniques employed to obtain the Ported Shroud configuration, especially to ensure a low cost for high volume productions, do not provide an optimal shape for the ported shroud recirculation channel and, for this reason, it is not possible to exploit its full potential in terms of reducing aerodynamic losses. Turbomachinery companies that intend to implement innovative solutions need to find a compromise between performance and manufacturing costs. In order to be able to develop a Cost Estimation Model to be used within the Metamodel-Assisted Multidisciplinary Design Optimization process of Computer-Aided Design Optimization (CADO)\nomenclature[]{CADO}{Computer-Aided Design Optimization} in-house software, bibliographic research has been carried out on the manufacturing methods and technology used for centrifugal compressors components in the automotive turbocharger applications such as Compressor Housing, Impeller Wheel and Backplate. Part of this work aims to provide an overview of the various manufacturing techniques used and analyze their critical issues and limitations. This dissertation introduces traditional techniques such as die-casting or 5-axis milling with Computer Numerical Control machines up to innovative powder-bed-process type Additive Manufacturing techniques such as Selective Laser Melting. The Cost Model used allows us to combine a parametric approach for estimating the cost of Computer Numerical Control Machining and an Analytical Activity Based Costing approach for Additive Manufacturing operations and, for this reason, it is also possible to estimate the cost for solutions that use hybrid manufacturing combining an additive and subtractive approach on the component. The next step was to manage the creation of the code for the geometry parameterization of the recirculation channel and the one for the generation of the structured mesh. These C++ codes have been inserted in the CADO software and after the Design of Experiments (DOE) process, the optimizer has been used to carry out the analyzes to find the optimized solution in order to improve the compressor performance, especially for near-surge operations. Moreover, this work focus on the interpretation of the fluid dynamic phenomena found through Computational Fluid-Dynamics. The optimization process is not yet completed but recirculation channel designs with innovative shapes and high efficiency have been found, characterized by a reduction of the vortex structures inside the channel.