Investigation Of High Subsonic Compressor Cascade Tip Clearance Control Using Blade Tip Winglets

Compared with traditional powerplant,gas turbine with many different advantages is widely used in the fields of electric power station,ship power,mechanical drive and so on.With the acceleration of the global industrialization and the growing demand of the energy power market,many countries have invested a lot of efforts in the research and development of gas turbines.China has gradually realized the importance of gas turbine in the national industrial field and has paid more attention to the gas turbine industry in recent years.As the core components of gas turbine,the compressor is facing new challenges with the improvement of performance requirements.Tip leakage flow in rotors directly affects the aerodynamic performance of the compressor,so the performance of the gas turbine can be improved by reasonably controlling the tip leakage flow.In recent years,the blade tip winglet has been widely concerned as an effective passive control method.The mechanism using tip winglets to control tip flow has been systematically investigated under the condition of low-speed incoming flow,whereas the research under high subsonic incoming conditions needs to be further supplemented.In this paper,experimental measurements which are supplemented by numerical calculations are carried out to study the tip leakage flow of compressor cascade with tip winglet under high subsonic incoming conditions.The mechanism of the gap height,the incoming Mach number and the angle of attack influencing the winglet control of tip leakage flow is explored,and the aerodynamic performance database of high subsonic compressor cascade with the tip winglets under all operating conditions are established.First of all,experimental researches are taken on original compressor cascades with and without tip clearance,and numerical studies are also conducted as the supplement to experimental results.The influences of tip clearance on the flow structures of compressor cascades are analyzed,and these studies reveal the flow loss mechanism in the tip clearance of compressor cascades.Meanwhile,preliminary exploration of the effects on tip clearance flow controlling with different installation locations of tip winglets is made under high subsonic conditions.The results indicate that the corner separation between the end-wall and suction surface of the blade is the main aerodynamic loss in the case of non-tip-clearance.For the case with tip clearance,by contrast,the existence of clearance flow and tip leakage vortex makes the three-dimensional separation loss between the blade suction surface and end-wall decrease,and the strength of upper passage vortex and concentrated shed vortex is inhibited and all these make flow structure more complicated which results in higher total pressure loss.With the increasing of tip clearance,the leakage vortex intensity increases,together with the influence scope,the unevenness of the outlet flow field and the flow field loss.At design the angle of attack,the suction side winglet increases the pressure differential at blade tip.The strength of tip leakage flow is enhanced and the influence scope of tip leakage vortex is enlarged,which leads to the increasing of the non-uniformity level at the flow field outlet and the total flow energy loss.On the other hand,pressure side winglet decreases the pressure differential at blade tip.The strength of tip leakage flow is weakened,and the influence scope of tip leakage vortex is reduced which leads to the decreasing of the non-uniformity level at the flow field outlet and the total flow energy loss.In a word,the improvement effect of pressure side winglet is better than that of suction side winglet.under high subsonic conditions.Then,the influence of the suction winglet with different width on tip clearance flow is studied by numerical simulation method,and the characteristics of variable clearance,variable Mach number and variable the angle of attack with the suction winglet are investigated.The results show that the change of Mach number has a more obvious effect on the suction winglet than the height of the tip clearance and the the angle of attack.With the increase of the incoming Mach number,the effect of the suction side winglet on the flow field is gradually weakened,the interference effect is enhanced.Meanwhile,the flow intensity of the tip clearance,the leakage vortex intensity,the influence area,the non-uniformity of the outlet flow field and the flow field loss increases.With the increase of the width of winglets,the flow field changes more severely.When the tip clearance is gradually increased,the influence of the suction winglet on the flow field increases,and the flow loss gradually increases.Because the blade tip winglets have positive and negative effects on the flow field,the mutual influence of the blade tip winglets on the different widths of the blade tip winglets varies.With the increase of the angle of attack,the influence of the suction winglet on the flow field gradually increases,and the influence scope of the leakage vortex increases gradually,which is proportional to the width of the blade tip winglet.Finally,the influence of pressure side winglet with different width on the tip clearance flow under high subsonic incoming conditions is studied by means of both experimental and numerical methods,and the mechanism of pressure side winglet controlling the tip clearance flow at off-design conditions is investigated.The results show that the tip winglet prolongs the flow distance of leakage flow in the tip clearance,partially dissipates the energy of the leakage flow,delays the encounter between the leakage flow and the mainstream,and reduces their mixing loss.The low energy fluid located near the pressure side winglet not only weakens the pressure gradient on both sides of the blade,but also inhibits the flow into the tip clearance.With the increase of the height of the tip clearance,the leakage flow is enhanced and the flow field is obviously improved by using pressure side winglet.With the increase of Mach number,the leakage flow in the flow field increases gradually,and the improvement effect of the pressure side winglet increases simultaneously,which reduces the flow loss and increases the uniformity of the outlet flow.The improvement degree is proportional to the width of the winglet.During the rising of the angle of attack changing form negative value to positive value,the improvement effect of pressure side winglet is enhanced,and the influence scope of the leakage vortex is diminished.The leakage vortex intensity is weakened,and the degree of overturning of the outlet flow is also decreased.When the pressure side winglet width increases,the influence of winglet on the flow field increases.The flow in compressor cascade with pressure side winglet behaves better in terms of aerodynamic performance at variable clearance,variable Mach number and variable incidence angle conditions,and the stable working range of the compressor is improved.