Downsizing modern automotive engines poses a challenge to turbocharger designs. Turbocharger compressors are required to provide a wide operating range with high-efficiency levels. The compressors are equipped with either passive or active casing treatments (ACTs) to achieve this goal. On the turbine side, the ever-increasing EGR flow into the engine demands an efficient scroll design that addresses both the performance and packaging limits.The present study conducts numerical aerodynamic and acoustic performance investigation of a turbocharger compressor equipped with a dual-slot active casing treatment (ACT) to widen the compressor's low and high flow rate operating limits independently. The first slot (surge-slot), positioned between the leading edge of the main and splitter blades, improves the surge margin of the compressor. Similar to the widely applied self-recirculating casing treatment, the surge slot removes stagnant fluid from the boundary-layer region of the inducer and delivers it to the impeller inlet when the compressor operates near the surge limit. The second slot (choke-slot), positioned downstream of the aerodynamic throat, increases the choke margin of the compressor. A new combination of loss models is proposed to predict the compressor performance, providing satisfactory results. A novel methodology is developed to estimate the full compressor map from CFD results by incorporating Greitzer's surge model. The compressor performance analysis revealed that the choke-slot closed configuration resulted in an isentropic efficiency penalty at higher compressor speeds. The efficiency penalty is addressed by optimizing the choke slot thickness to reduce the mass flow recirculating in the channel.On the other hand, the casing treatment provides an additional path for the unsteady compressor flow, increasing the noise level of the compressor. In this work, acoustic analogies are used to study the noise generated by different compressor casing treatment configurations. The transient aeroacoustic simulations are completed for both a choke-slot closed design near surge and a choke-slot open design near the maximum efficiency point. The simulation results revealed that the broadband and blade passing frequency (BPF) noise levels in the inlet and exit pipes decreased as the probe points moved away from the impeller.Further, the double inlet turbine performance is assessed numerically at even and uneven turbine inlet flows for three cases representing different engine operating conditions ranging from low load to full load. The CFD setup in this study is validated by using nine experimental data points with equal admissions at the two volute inlets. A significant amount of performance drop is observed when the turbine operates at uneven turbine inlet flow cases. The performance drop is more pronounced when the turbine operating point moves from low to high loads. Additionally, an energy audit of the turbine assembly is completed by estimating the local entropy production rate at eleven sub-regions. In all flow cases, the tip region losses dominate the impeller losses at even and uneven flows. The volute flow is affected sharply by the mass flow imbalance across the turbine inlets, most notably at high engine loads.In the last section of this work, the impact of volute design geometric parameters on the aerodynamic performance of the turbine with nozzle blades is explored by using a three-dimensional computational fluid dynamics method. The volute tongue angle, tongue clearance, and volute shape are assessed in detail to determine how they impact the turbine's isentropic efficiency and the pressure loss coefficient of the volute. The numerical results show that the optimal tongue angle is approximately 15℗ʻ for single-scroll volutes. The study results also indicate that higher tongue clearance improves turbine performance as it enhances flow development. Finally, symmetrical cross-sectional shapes boosted the turbine's aerodynamic performance in single-scroll turbines by uniformly distributing the volute exit flow from the hub to the shroud.
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