Study On Adaptive Casing Treatment Of Marine Gas Turbine Compressor

Marine gas turbines are required to have good operation stability under high-speed pursuit and low-speed cruise conditions.As one of the core components of marine gas turbines,it is very important to improve the stability margin of the compressor at each rotating speed.The main methods of enhancing stability and anti-surge of marine compressors at non-design speed are the rotatable guide vane technology and intermediate stage venting measures,which make engine thrust descent and bring greater losses.In order to solve this problem,the adaptive casing treatment technology which belongs to the passive control technology and has the characteristic of spontaneously adjusting the flow under different operating conditions according to the flow field state,was used to improve the stability margin of compressor at various speeds in this paper.The certain 2.5-stage transonic axial marine compressor in the laboratory was taken as a model in this research,and its operation status and stall characteristic are analyzed in detail at three rotating speeds by combining the experiments and numerical simulation methods.According to the stall positions and the stall reasons,the influence of the adaptive casing treatment on the improvement of the compressor stability margin at three speeds was investigated by numerical simulation analysis method,and the casing treatment's anti-distortion performance was also tested at the same time.The main works in this paper are as follows:1.A 2.5-stage axial flow transonic compressor as the research object,and the working characteristics of this compressor at three rotating speeds of 100%,75% and 50% were experimentally measured.In addition,a numerical simulation method was used to study the working characteristics of compressor on three rotating speeds.By comparing with the experimental results,the feasibility of the numerical simulation method used in this paper was verified.2.Based on the numerical simulation method,the stall positions and stall reasons of the compressor at three rotating speeds were studied by means of synchronously analyzing the density*Vw decrement of circumference average on meridional plane,Q-criterion vortex identification and local flow field.The result showed that the compressor stall area mainly concentrated near the tip of the first-stage rotor and near the hub of the outlet guide vane.At100% rotating speed,the stall characteristic near the hub of the outlet guide vane played a dominant role.At 75% and 50 % rotating speed,the stall characteristic near the tip of the first-stage rotating blade played a dominant role.At three rotating speeds,the tip area of the first-stage rotating blade all had obvious stall characteristics,and had a dramatic effect on the flow in the subsequent stage.Based on the above research result,in this paper,the casing treatment was installed on the top of the first-stage rotating blade.3.According to the existing design experience,the structural parameters of casing treatment were determined.The position of the bleed port was set at the top of the blade.A two-opening adaptive casing treatment was designed first,and then in order to increase the injection flow of the injection opening,a new three-opening adaptive casing treatment was designed.Based on the numerical simulation method,the effects of two casing treatments on compressor performance at three rotating speeds were analyzed and compared.The results showed that the two kinds of casing treatments at three rotating speeds both could improve the compressor stability margin,and the stability improvement range was between 1.96% and3.66%.Meanwhile,the peak efficiency loss between 0.17% and 0.34% was small.The higher the speed,the more increases in the amount of stability margin,the more accompanying peak efficiency loss.At 100% rotating speed,the two-opening adaptive casing treatment had a better stability improvement effect,and the peak efficiency decreased less.At 75% and 50%speed,the new type of three-opening adaptive casing treatment improved the stability margin more than the two-opening casing treatment.4.The influences of three structural parameters including cavity width,opening width and injection opening position of three-opening and two-opening casing treatments on the performance of compressor were studied,and the effect of the position of bleed port of two-opening casing treatment on the ability of stability improvement was studied.Based on the designed casing treatment structures,the influence of a single variable on the compressor performance was studied at 75% speed while the other structural parameters were fixed.The results showed that the changes in the cavity width handled by the two casing treatments had similar effects on the compressor performance.The 100% cavity width led to premature instability of compressor;the 50% cavity width could improve the stability margin;and the 25%cavity width made the stability margin basically unchanged.For the three-opening adaptive casing treatment,the increase of middle opening width could further improve the compressor stability margin.However,the increase of the main bleed opening width made the compressor stall in advance.For the two-opening adaptive casing treatment,the conclusion of increasing the bleed opening width was similar with the three-opening casing treatment.When the bleed opening width at the position of 0.4 chord lengths increased,the compressor stability margin improved.When the bleed opening width at the position of 0.6 chord lengths increased,the compressor stability margin decreased.For the three-opening casing treatment,when the width of 0.4 and 0.6 chord lengths opening decreased separately,the stability margin of compressor decrease.The change of the distance between the injection opening before the leading edge of the blade tip and the leading edge had a similar effect on the compressor characteristics for the three-opening and two-opening casing treatments.When the distance increased,the compressor stability margin decreased,and when the distance decreased,the compressor stability margin decreased or basically unchanged.For the position of the bleed port handled by the two-opening casing treatment,the compressor stability margin has less change when the bleed port was set at 0.8 chord length,and when the bleed port was placed at 0.4 and 0.6 chord lengths,the compressor stability margin increased to 3.17% and 3.28%,respectively.5.The numerical simulation study on the stability improvement ability of different casing treatment structures under non-uniform air intake conditions was conducted.The anti-distortion ability of the three-opening and two-opening adaptive casing treatment was analyzed and compared.The result showed that the three-opening adaptive casing treatment had better anti-distortion ability at 100% and 75% rotating speeds,two types of casing treatment had same anti-distortion ability at 50% rotating speeds.