Investigation Of The Influence Of Axial Gap On The Clocking Effect In Multi-Stage Axial Compressor With Straight/Bowed Stator Blades

The performance of aero-engine needs to be improved while the aviation industry develops rapidly in the modern time. The compressor, As one of the three key parts of turbine engine, its aerodynamic performance improvement is very important for aero-engine's development. The higher efficiency and total pressure ratio, the more load and surge margin, and the less size and weight becomes the aim of performance improvement of compressoe.For this purpose, a detailed experimental investigation has been carried out in a low speed double stage compressor with straight stator and positive bowed stator in different axial gaps at different work condition. Then, Numerical simulation is done to verify the flow field and makeup more details which can not be measured in experiment. At last, based on the calculation results, the thesis gives out the detail vortex structure in compressor stator passage with hub tip proceeding from topological analysis method. It also gives out the topological law for flow field at design condition and between different work conditions.Based on the results of experiment, the clocking effect exists clearly in compressor both with straight stator and bowed stator in original axial gap and strengthens while the massflow increases. The relation between efficiency variationg and relative wake position of two stator rows is studied to validate the classical theory of wake interference. The maximum efficiency is obtained when the upstream stator wake mixes with the downstream stator's wake and the minimum efficiency occurs when the upstream stator wake locates in the middle of the downstream stator's passage. Comparing with straight stator and bowed stator, the wake of bowed stator dissipates more easily because of its complex shape, and its clocking effect is weaker than straight stator. In the original axial gap scheme, the diffusion capability of compressor with positive bowed stator is weaker than the one with straight stator. But its input tonque is less than the latter's. These two factors make the efficiency of compressor with positive bowed stator is higher than the compressor with straight stator. The result of experiment also shows than the spanwise transition effect of positive bowed stator makes the low-energy fluid in both cornersl move towards midspan reduces loss near end walls. The strength ability of flow field controlity at near stall condition of positive bowed stator makes an effert for the surge margin increase.While the rotor-stator axial gap of the same stage reduces, the distance between the first stator and the second rotor lengthens. The wake of the first stator dissipates exacerbattingly. It can not makes a clearly interference in the second stator's passage. That makes the clocking effect take off. While the rotor-stator axial gap of the same stage reduces, the diffusion capability of compressor increases but the input tonque also raises. These make the efficiency of compressor improves first and falls down later. It means that there is a best axial gap wxists to make the unit get a highest efficiency. Otherwise, the ability of flow turning and through-flow decreases a little.While the axial gap reduces, the total pressure ratio of compressor with positive bowed stator increases more than the compressor with straight stator. And its input tonque raise is less than the latter. That makes the compressor with positive bowed stator get more efficiency improvement than the compressor with straight stator in small axial gap. At near stall condition, the flow field of straight stator outlet deteriorates quickly while little change occurs for the positive bowed stator. That means the flow field controlling capability of positive bowed stator gets more advantage than straight stator in small axial gap. At dedign condition, the best axial gap of compressor with positive bowed stator is smaller than the compressor with straight stator. It shows that, with positive bowed stator, the compressor can get more efficiency in less axial size. This result also can reduce the weight of the whole aero-engine.With the limitation of experiment, such as poor data size and ambiguousness of flow field in detail, the numerical simulation is done with CFX11.0. With the validation between experiment and calculation results, it shows that the calculation results can be used for qualitative analysis of flow field.Based on the topological analysis for calculation results, there are three large scale vortexs exists in compressor stator's passge with hub tip. They are the passage vortex at up side, the scraping vortex near hub tip and the concentrated shed vortex. There ara also several small scale votex exists, such as the horseshoe vortex at the pressure side, the corner vortex at the pressure side, the vortex near the outlet of up corner and some vortex in the stator's hub tip.While the property of pressure gradient changes (from positive pressure gradient to negative pressure gradient or negative to positive),the total number of singular points will increase and the flow field becomes complex. Sooner or later, while the fluid"fits"the pressure gradient, the structure of flow field changes simply. If there is no change for property of pressure gradient, the total number of singular points will keeps a stable value. Before the separation happens, the total number of singular points increases while the mass flow reduces in compressor stator's passage. The total number of singular points gets the maximal value while the separation happens. When the mass flow reduces continuely, the total number of singular points begins to reduce and the flow field begins to change simply. That means in a special point of view, the flow field will be simple while the separation exacerbates. And the results of experiments in different work condition also prove this conclusion.