Study On Changes Of The Turbine Aerodynamic Performance Into The Rotor-stator Interaction And Mechanism Of The Vibration Induced

With the rapid development of the modern turbine engine, higher demands are put forward to the turbine aerodynamic design. So far, aerodynamic loading of the airliner LP turbine has been increased largely by studying and applying the unsteady aerodynamic effects induced by the rotor-stator interaction. Although many researches have been done on the unsteady aerodynamic mechanism, most of the turbine design do not refer to the unsteady effect due to the long time computing and the habitual thoughts in the conventional design. The periodic unsteady effect does not only affect the aerodynamic performance but also has quite an effect on the vibration and noise of the blade. In order to consider the unsteady rotor-stator interaction effect more in the turbine design, discrepancy between steady and unsteady simulation is analyzed, considering the importance and necessity of adding interaction effect to design and the effects on the aerodynamics, vibration and noise. In addition, the mechanism of rotor-stator interaction is further elaborated under some circumstances.With the guarantee of the reliability of the numerical method, this paper simulates the steady and unsteady conditions on a high-load LP turbine stage, and illustrates the reason causing the difference which can be found by comparing and analyzing the results. And points out that the secondary flow of the upstream blade had an inhibitory effect on the secondary flow loss of the downstream blade endwall. Showed the main influencing factors of the rotor-stator interaction for the surface pressure pulsation, and uesd a detail analysis to show the impact of the factors for the different blade height sections.The changes of the rotor-stator interaction were analyzed under the differenet axial spacing conditions, showed that the change regulation of the potential flow interference and secondary flow mixing along with the change of the axial spacing. And given a mechanism analysis to the inhibitory effect of the secondary flow of the upstream blade on the secondary flow loss of the downstream blade endwall, and showed the " inverse effect" phenomenon induced by the tip momentum mixing. The next, studied on the effect of the change of the rotor tip clearance on the rotor-stator interaction, the results showed that the leakage loss had insteaded of the rotor-stator interaction to become the main energy loss along with the increase of tip clearance, and the effect range of the leakage flow also extended toward the hub. And then, The rotor-stator interaction had an obvious effect to the leakage flow, it made the leakage flow periodic variation.Because the unsteady behavior in the upstream stages and the effect of the vortical structures on the downstream cascades were more complex, it was not enough to only do a singer stage analysis. The next, the paper simulated a two stage high pressure turbine, analyzed the changes of the aerodynamic performance in the steady and unsteady conditions, and confirmed the existence of the―inverse effect‖at high pressure turbine. The generation and development process of every cascade, and the effect of them on the next cascade in the rotor-stator interaction were detailed analyzed, and the flow phenomenon that the passage vortex induced the endwall secondary flow to its top, and generated the induced vortex was founded in this turbine model; using the method of reducing backpressure to study on the effect of the potential flow behavior for the blade surface pressure pulsation. the change situation of the blade surface pressure pulsation and the effect factors were given.In order to illustrate the importance of rotor-stator interaction, the blade vibration caused by periodical unsteady pressure impulse has been investigated in this paper. An unsteady force model is put force by analyzing the relationship of pressure change and the force on blade. A numerical analysis about the blade vibration caused by unsteady aerodynamic force has been done to give the vibration extreme value in both rotor and stator. Furthermore, scattered noise produced by unsteady force has also been investigated to determine that it is the interaction of potential flow between stages and the blade tip leakage flow which is the main noise source in turbine cascade.Finally, the method to control fluctuation of the blade surface pressure was studied. With the method of increasing the axial gap and using the positive curved blade at the first stator, the unsteady pressure fluctuation of turbine blade can be controlled. The result indicates that both methods are useful to reduce the pressure pulsation of the blade surface, but the mechanism and influencing scope are different. The former reduces the pressure pulsation by weakening the rotor-stator interaction, the role of which is mainly reflected in the upstream stator trailing edge and the downstream rotor leading edge, but it is not helpful for the pressure pulsation caused by the blade tip leakage flow; the latter reduce the pressure pulsation by changing the potential flow field and the flow distribution of the stator outlet, which reduce the rotor-stator interaction leading to lower pressure propulsion.In summary, the importance of considering the rotor-stator interaction in the process of designing the turbine is illustrated in this paper and some fundamental mechanism of rotor-stator interaction is discussed, which is a meaningful work for rotor-stator interaction design in turbine.