| Turbocharger technology are more widely appreciated and applied with modern vehicle engines towards higher power, higher torque and lower emissions, so how to design a high efficiency, pressure ratio and wide flow range is important. In general, the turbocharger centrifugal compressor mainly composed by the centrifugal impeller, no leaves diffuser and volute, compressor rotor blade is paid more attention by researchers in the past due to its important role and its complexity, In contrast, non-leaf diffuser and volute ware researched less, but the diffuser is a key component during all the compressor stationary parts. The kinetic energy in the impeller outlet account 20% to 50% of the power got from the rotor, diffuser allows the air to reduce its speed, thus kinetic energy could change into pressure energy, to further enhance the pressure. The problem to use the no vane diffuser in the vehicle turbocharger are the complex vehicles operation status, significant changes of air flow, velocity and pressure, the flow field is extremely complex. Therefore, further study no vane diffuser to fully grasp its internal flow pattern, which lay the foundation to design better diffuser and to further improve compressor performance.In this paper a full three-dimensional CFD software Numeca was used to simulate a small car used turbocharger centrifugal, the flow performance in the non vane diffuser was analyzed. Firstly this paper elaborated the characteristics of the internal gas flow in the non vane diffuser section and the mechanism of choosing convergent diffuser when designing.Secondly, the flow inside the diffuser are analyzed in a new perspective on a small flow conditions, that is, the convergent section and the parallel segments were Separated analyzed, in order to clear the difference between them in the low flow conditions, so it set basis for further study for stall phenomenon.The third, the contraction angle has a certain impact on overall performance of the the compressor by comparing different case with different contraction angle. A diffuser design principles was pointed out, it set the foundation for designing a good performance convergent non vane diffuser.Centrifugal compressor performance curve is the direct reference to evaluate the aerodynamic performance of centrifugal compressor, to analyse the trend features of the compressor performance curve, to understand the formation mechanism of the curves are good for in-depth understanding of compressor performance. Finally, the two characteristics of the compressor, the most high-pressure point is behind the most high-efficiency point, the pressure ratio doesn't decline as fast as efficiency behind the most high-pressure ratio point, in the same rotational speed conditions, are elaborated, the mechanism of these two characteristics were analysed, it is the supplement for knowing the formation mechanism of the compressor performence curves.The core of this paper is, on the one hand, contraction angles on compressor performance ware researched by means of numerical simulation on the first time, the flow mechanism of the influence was analysed. Based on this study of the mature contraction angle diffuser compressor is improved, and formating two improvement program, One program in the design point pressure get 1.74% more efficiency than the original case, the second program get 0.042 more pressure ratio,but its efficiency is considerable to the original one. On the other band, the two characteristics of the compressor, the most high-pressure point is behind the most high-efficiency point, the pressure ratio doesn't decline as fast as efficiency behind the most high-pressure ratio point, in the same rotational speed conditions, are elaborated, the mechanism of these two characteristics were analysed on the first tine, it is the supplement for knowing the formation mechanism of the compressor performence curves. |
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