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This paper describes a global optimization of a recirculation flow type casing treatment in centrifugal compressors of turbochargers. The global optimization for the recirculating flow type casing treatment has been performed based on the existing casing treatment. The optimization approach to the recirculation flow type casing treatment for the centrifugal compressor, incorporating meta-model assisted evolutionary algorithm, computational fluid dynamics analysis technique, artificial neural network, and genetic algorithms has been presented. For the baseline design of the casing treatment, numerical approach is validated with an experimental result from a test rig. The technical issue of the casing treatment is found to be the dropping of the adiabatic efficiency at smaller flow rate condition. In this study, the objective of the optimization is to improve adiabatic efficiency under multipoint mass flow rate conditions. The shape of the casing treatment has been parameterized by six parameters. The numerical optimization result gives the optimized recirculation casing shape, which has a possibility to improve the efficiency not only at design flow rate but also at smaller flow rate. The improvement in adiabatic efficiency at off-design point is discussed by means of the improved flow incidence at the inlet of the rotating impeller. The influence on adiabatic efficiencies at both design and off-design conditions is discussed by the sensitivity of the recirculation flow rate. It is found that the optimized design of the casing treatment provides optimized recirculation flow rate.

This paper presents the performance of the diffuser augmented wind turbine (DAWT) with the various diffuser shapes using the numerical investigations. DAWT is also a type of wind turbine and the diffuser shapes, the nozzle shapes and the cylindrical shapes are commonly inserted around the horizontal axis wind turbine (HAWT) to become the more efficient wind turbine. The aim of this study is to find the more efficient design of the diffuser for the horizontal axis wind turbine using the numerical investigations. In this research, the converging and diverging diffuser shape is inserted and the airfoil design is calculated by using the Blade Elementary Momentum Theory. The airfoil type NACA 4412 is chosen because it is suitable for the low wind speed area and easy to produce. The turbulent model k-ω is combined with the Navier Stoke equation to solve the 3-dimensional steady flow simulation of the diffuser augmented wind turbine using the Computational Fluid Dynamics (CFD) simulations. The numerical investigation is used to compare and predict the power coefficient of the DAWT with various shapes. The baseline design of the diffuser (L = 170 mm, H = 57 mm and α = 11̊) is firstly investigated. To predict the power coefficient of the various diffuser shapes, the range of the length of the diffuser is (L/D = 0.5 to 1.5), the range of the brim height of the diffuser (H/D = 0.1 to 0.35) and the range of the angle of the diffuser (α = 5̊ to 15̊ ) are also investigated. The parameters of the diffuser shapes are assigned by using the Central Composite Design Face Centered Method. The response surface method is also used to predict the most efficient diffuser design. The performance of the horizontal axis wind turbine, that of the diffuser augmented wind turbine and that of the diffuser augmented wind turbine with various shapes of diffuser are compared. The performance of new diffuser augmented wind turbine (IND_009) is 50% and 55% higher than the baseline diffuser augmented wind turbine and the horizontal axis wind turbine at rated velocity. The flow visualization of the HAWT, DAWTs are also discussed.

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A Low Solidity circular cascade Diffuser (LSD) in a centrifugal blower is designed by means of multi-objective optimization technique. An optimization code with a meta-model assisted evolutionary algorithm is used with a commercial CFD code ANSYS-CFX. The optimization is aiming at improving the static pressure coefficient at design point and at small flow rate condition while constraining the slope of the lift coefficient curve. Seven detailed design parameters describing the shape and position of the LSD vane were introduced. Moreover, a small tip clearance of the LSD blade was applied in order to activate and to stabilize the secondary flow effect at small flow rate conditions. The optimized LSD blade has been manufactured and the characteristic of optimized LSD is confirmed by the experimental test rig. Optimized LSD has an extended operating range of 114 % towards smaller flow rate as compared to the baseline design without deteriorating the diffuser pressure recovery at design point. The detailed flow in the diffuser is also confirmed by means of a Particle Image Velocimetery (PIV). The flow was compared between in the cases with and without tip clearance. In spite of the fluctuating flow at the diffuser inlet, secondary flow spreads to the whole area of LSD blade pitch stably. Stable secondary flow suppresses flow separation at the suction surface of the LSD. It is found that the optimized LSD blade shows good improvement of the blade loading in the whole operating range, while at small flow rate the flow separation on the LSD blade has been successfully suppressed by the secondary flow effect.