Study On The Effects Of Bow And Sweep Blade On Centrifugal Impeller Performance And Aerodynamic Optimization

The centrifugal compressor is the main components form of small gas turbine and turbocharger. To improve the efficiency, develop the load capacity and widen the operating margin is the consistent trend of the compressor development, while the ruled surface impeller is difficult to meet the growing performance requirements. Swept and bowed blade can effectively reduce the secondary flow loss and shock loss, thus improve compressor performance. But the mechanism of swept and bowed technology in the centrifugal compressor is not clear, therefore studying on the effects of bow and sweep blade on centrifugal impeller performance deeply and revealing the flow mechanism has very practical significance. In addition, the aero engine with a centrifugal compressor or turbocharger often works in the conditions of low Reynolds number at high altitudes, and there will be great changes in compressor performance. Thus it is important to find out the swept or bowed blade that could improve the performance of the impeller in the low Reynolds condition. This paper carried out the following research:Firstly, application of different bowed blade on the centrifugal impellers was studied. Different bowed blade was designed with the Concept Axcent software changing the two main parameters of "bent position" and "bending amount" distribution along the flow direction. 12 cases of leading edge bowed and 4 cases of trailing edge were designed. The result: negative bowed impeller on the leading edge help improve peak efficiency and pressure ratio and the closer to the tip, the more obvious improvement. The negative bowed impeller on the 70% span-wise of the leading edge has the highest efficiency, 0.84% higher than the original case.Then application of different swept blade in the centrifugal impellers was studied. First the leading edge of main blade or splitter blade was shaped alone. Then get the trends of the performance changing by numerical calculation and analysis of the internal flow mechanism. Aft sweep of the leading edge of the main blade is found to be beneficial to the impeller’s peak efficiency but it will reduce the operating range. Backward movement on the midspan of leading edge would expand the operating range effectively. The studies conducted on the splitter leading edge profile indicate that aft swept may help to improve the performance. The case combining backward movement on the midspan of leading edge of main blade and aft sweep of the leading edge of splitter blade can get the best performance.Finally, the effect of low Reynolds number on compressor performance and how swept and bowed blade improve the performance were studied. Firstly the centrifugal impeller performance at low Reynolds number conditions and its mechanism was studied, and the results show that the impeller aerodynamic performance dropped significantly at 20 km condition. Compared to the standard atmospheric conditions, peak efficiency decreased by 1.57%, 8% and 20%, respectively at 10 km, 20 km, 30 km altitude and the maximum pressure ratio reduced 0.15,0.66,1.49 respectively and the margin also reduced gradually.Aft swept of the leading edge of the main blade did not have a significant impact on the performance of the impeller in 20 km conditions. The margin of Case(B) decreased slightly compared with the standard conditions. Aft swept of the leading edge of the splitter blade could improve the peak efficiency. The case combining Backward movement on the mid-span of leading edge of main blade and Aft swept of the leading edge of splitter blade also get the best performance, the margin and peak efficiency improved by 3.9% and 0.6%.