Numerical investigation of diffuser solidity effect on turbulent airflow and performance of the turbocharger compressor

Low solidity diffuser in centrifugal compressors can achieve both high efficiency and wide operating ranges which is of great importance for turbocharger compressor. Low solidity is achieved by using a low chord to pitch ratio. In this work, a CFD simulation is carried out to examine the effect of solidity on airflow field of a turbocharger centrifugal compressor which consists of a simple-splitter impeller and a vaned diffuser. By changing the number of diffuser vanes while keeping the number of impeller blades constant, the solidity value of the diffuser is varied. The characteristics of the compressor are evaluated for 6, 8, 10 and 12 stator vanes which correspond to solidity of: 0.78, 1.04, 1.29 and 1.55, respectively. The spatial distribution of the pressure, velocity and turbulent kinetic energy show that the diffuser solidity has significant effect on flow field and compressor performance map. The compressor with a 6 vanes diffuser has higher efficiency and operates at a wider range of flow rate relative to that obtained with larger vans number. However a non-uniform flow at the compressor exit was observed with relatively high turbulent kinetic energy

A CFD-Based Numerical Evaluation, Assessment and Optimization of Conjugate Heat Transfer for Aerodynamic Cooling of a Wheel-Hub-Motors in Micro-Mobility Vehicles

Micro-mobility vehicles such as electric scooters and bikes are increasingly used for urban transportation; their designs usually trade off performance and range. Addressing thermal and cooling issues in such vehicles could enhance performance, reliability, life, and range. Limited packaging space within the wheels precludes the use of complex cooling systems that would also increase the cost and complexity of these mass-produced wheel motors. The present study begins by evaluating the external aerodynamics of the scooter to characterise the airflow conditions near the rotating wheel; then, a steady-state conjugate heat transfer model of a commercially available wheel hub motor (500W) is created using commercial computational fluid dynamics (CFD) software, StarCCM+. The CAD model of the motor used for this analysis has an external rotor permanent magnet (PM) brushless DC topology. Both internal and external fluid domains are considered to evaluate the combined flow dynamics and conjugate heat transfer from the windings (heat source) to the ambient air. At the maximum speed (482rpm) of the motor, for a total power loss of 180W (η=64%), a maximum temperature of 295°C is observed in the windings. Evaluating the thermal path shows that approximately 58.1% of the total heat generated in the winding is dissipated radially via convection through the air gap, and only 3.66% through the shaft via conduction. The thermal resistance for the shaft is in the range of 22-60 K/W and the rotor components is in the range of 0-2 K/W for the operational speed range of 0-1000rpm. Taguchi's Design of Experiment (DOE) with Design manager study has been conducted to optimize the performance of design parameters (Fins and air-vents/holes) in cooling the motor. Air vents and external fins on rotor-lid (rotor cover) has a greater effect on cooling the motor than other design parameters