| As a principal part of the aero-turbo engine, the flow loss in the blade channel is affecting totalaerodynamic performance, stability, and economy. The adverse pressure gradient and blade loadingin compressor blade channel keep increasing when the modern aero-tubo engine design demandshigher and higher thrust-weight ratio. The corner separation or hub-corner stall will arise and causegreat total pressure loss. The three-dimensional blading design technique changes the location ofblade stacking line to introduce the radial force, which will change the static pressure distribution onthe suction and hub surface, to control the vortex development and strength of shockwave, so it hasthe ability to improve total performance and stability of the compressor. The flow development in thecompressor blade passage is the development and mixing of all kinds of vortex, so it is necessary tostudy the loss decrease mechanism and effect law of the three-dimensional blade through detailednumerical simulation and flow field measurement in the view of vortex development.Numerical investigation is carried out on a two-stage low speed axial compressor. The SBC andBLB type stacking lines of the first stage stator S1are chosen to study the effect of bowed parameter,bowed height and bowed angles, on the total performance and vortex with and without hub clearance,after that the loss decrease mechanism is discussed. Based on the numerical simulation results, a set ofBLB blades with best effectiveness is produced and installed on the compressor. Then experiments arecarried out in the straight blade compressor and bowed blade one. The flow field at five differenttransverse sections is measured by four different lengths of five-hole hole probes and a four-holeprobe. Finally, experiments of the both compressor with inlet distortion are carried out. Through theexperiment total performance of compressor and flow field of outlet transverse sections of S1aremeasured, the mechanism of loss decrease with inlet distortion is discussed.It is found that hub-corner stall is the main cause for the rapid increase of total pressure loss inthe compressor stator passage with hub clearance at near stall condition. Bowed stator has suppressesthe accumulation of low energy fluid at both ends of blade and the cross-flow on the hub surface bydecreasing the blade loading at both blade ends and the area of low static pressure on the hub surface,so it decreases the strength of hub separation vortex and concentrated shedding vortex. Moreover, thehub separation vortex does not go up and mix with concentrated shedding vortex so the loss isdecreased greatly and the hub-corner stall disappears. Efficiency has been increased by one percentaround both in the SBC b and BLB type blade. The result with hub clearance shows that tip separation vortex, hub leakage vortex and lowerpassage vortex are the main cause for the increase of loss in the blade passage. The bowed bladereduces the blade loading at both ends to suppresses the accumulation of low energy fluid, and thecross-flow at the hub surface, so the distance between lower passage vortex and hub leakage vortexgets bigger, which makes the mixing loss between the two vortexes decrease. At the near the stallpoint, the BLB blades with10%blade height and15°degrees has increased the efficiency by0.3percent. It is proved that bowed blade improves the performance of compressor mainly at low flowrate, whether with hub clearance or without. While at great flow rate the effect of bowed stator is notclear. Moreover, the efficiency of bowed blade compressor may be smaller than the straight one. It isbecause that bowed blade can decrease the flow loss, it also bring the surface friction loss on the otherhand. It is a comprehensive result for bowed blade.The experiment has verified that the bowed stator with hub clearance can improve theperformance indeed. The biggest efficiency profit is about one percent at the flow rate of0.637. Themain flow loss is caused by the tip corner separation, hub leakage vortex, and the mixing between hubleakage vortex and lower passage vortex. At low flow rate, bowed blade has decrease the strength ofthose vortexes, and it also has delays the appearance of hub leakage vortex and lower passage vortex,so the flow loss has decreased.Bowed blade can also improve performance of the compressor with inlet distortion. Theefficiency profit of bowed blade is one percent both under radial distortion and circumferential one.Bowed blade improves performance of the compressor mainly at great flow rates. As the flow rategets smaller, there is nearly no different between bowed blade compressor’s performance and straightone. While the effect of bowed blade becomes more and more clear when the flow rate gets smaller.The reason is that tip radial distortion makes the loss near the blade tip more serious, while the lossnear the hub less serious. As the flow rate gets smaller, the bowed blade’s capability of reducing lossis reaching its limitation. On the other hand, the loss near the hub is not serious, so there is noobvious efficiency profit near the hub. Under the circumstantial distortion the compressor is dividedinto two segment compressors. One segment is under a bigger flow rate, the other is under a smallerflow rate. So when the bowed blade in the former reaches its limitation, while the latter still has someresidual capacity to reduce the loss. So the entire compressor’s performance keeps improved. |
PDF Full Text Request