Geometric Parameters Optimization And Performance Simulation In A Small Centrifugal Compressor

With the demonstrable advantages, diesel engine has been widely used in many industrial departments. However, due to power resource decreased and current strict emission control criteria limit, the people have to set higher and stricter requirement for the diesel performance in power output, fuel economy and emission behavior. It has been proved that installing an exhaust gas turbocharger on the diesel engine, which is one of the best ways to achieve the target.With the advantages of higher stage pressure ratio, superior manufacturing technique, simple structure and higher adiabatic efficiency, centrifugal compressor has been widely used in the exhaust gas turbocharger. At present, the experimental method is mainly used to design compressor and obtain the flow characteristic map, but this method expands more money and longer time. In recently years, CFD have been widely used in the compressor research. If we could design and optimize the structure of compressor, then calculate flow characteristic map via CFD, it would prove a significant guideline for the actual design and engine matching. Therefore, it is quite a meaningful work to establish a CFD method for implementing the compressor's design, optimization and the flow characteristic map calculation.Firstly, a centrifugal compressor with 16 long blades impeller was designed, the air flow quantities of the compressor in different running speeds and different pressure ratios were calculated, and the map graph of flow characteristics of the compressor was established. Then, a optimizing compressor model with long and short blades was established through adjusting the number of the blades of impeller and structure parameters of diffuser and volute by the simulation analysis. The calculation results show that the performance of optimized compressor was improved, high efficient region expands into the lower speed ranges, the surge line deviates to lower flow region and the flow range in high-speed becomes wider.Based on the flow characteristics map graph of the optimized compressor, the effect losses was been analyzed in different speeds. It shows that the loss of impeller accounted the major part, diffuser was relatively small, volute was changed in wide range with the operating condition changing.In the end, the paper compares the performance of the vaneless diffuser with that of four types of vaned diffusers designed, including thickness straight wall blade, thickness arc wall blade, wedge blade and airfoil blade. The calculation results show that the wedge blade diffuser could effectively improve the efficiency of the compressor, while the airfoil blades has the worse efficiency, due to the flow separation occurring from the head of the suction surface and leading to the adiabatic efficiency and flow rate fall, and the other two types of diffusers have little influence on the compressor performance.