Optimization Design And Experimental Study On The Non-axisymmetric Endwall Of An Embedded Stator In The Multistage Axial Compressor

The application of non-axisymmetric endwall technology in turbine shows that it has the ability to improve the flow near the end region.It has been gradually transferred from the research of linear turbine cascade to the turbine of model aero-engine.It is confirmed that the non-axisymmetric endwall technology can effectively reduce the secondary flow loss in the turbine through the turbine component tests.The flow in the turbine is positive-pressure-gradient,while the flow in the compressor is reverse-pressure-gradient,which makes it more difficult to apply non-axisymmetric endwall technology in compressor than in turbine.At present,the research objects of non-axisymmetric endwall profiling in compressor are mainly concentrated on linear cascade,single-row compressor and single-stage compressor.These researches could not consider the development of boundary layer and the matching between different stages in multistage compressor,which is one of the important reasons why the non-axisymmetric endwall technology has not been applied to the compressor of model aero-engine.At present,there is a lack of engineering experience in the optimization design of non-axisymmetric endwall in multistage compressor,and also lack of the experimental research on the non-axisymmetric endwall in multistage axial compressor.Under such background,the optimization design and experimental research of non-axisymmetric endwall for multistage axial-flow compressor stator were carried out,which filled the blank of non-axisymmetric endwall in multistage axial compressor.It lays a foundation for the engineering application of endwall profiling optimization design in multistage compressor.The main research contents are as follows:In the first part,the characteristic of a four-stage axial-flow compressor and the detailed flow field at the outlet of each blade row were measured,and the flow features of each blade row were obtained.The stator of the third stage(an embedded stage)was selected as the prototype stator for non-axisymmetric endwall research.The blade surface static pressure and the flow field inside the stator channel of the third stator were measured.The results showed that the flow of the third stator was poor near the endwall of the casing at design point.The flow defect originated from the casing/suction corner at 61% axial chord length.The stator loss was high in the hub at near stall point,which was caused by the poor flow in the hub/suction corner.In the second part,the experimental platform and the optimization design platform of the embedded stator were constructed.The embedded stator experimental platform was convenient for the experimental research of groups of parametric profiled endwalls.The detailed flow field measurement for non-axisymmetric endwall stator in multi-stage environment was realized by replacing partial(rather than full annular)modified endwalls and blades,and 3D printing technology was used to process the modified endwalls and blades.It reduced the cost and shortened the period of the experiment of stator flow field measurement through these two aspects of improvements.Numerical simulations of the four stage compressor and the third stage were carried out respectively to verify the prediction ability of the numerical simulation on the characteristics of the four stage compressor,the flow field at the inlet and outlet of the third stator,and the stator loss coefficient.The inlet conditions of the third stage simulation came from the outlet data of the first two compressor stages measured in the four stage compressor experiment,which ensured that the simulation for the third stage in the optimization process reflected the flow environment in the four stage compressor.After the optimization design,the experimental measurements were carried out by the embedded stator experimental platform to verify the optimization effects of the optimization results in the multi-stage experimental environment.In the third part,the optimization design of the casing endwall of the embedded stator was studied at design point.A new optimization method was proposed,of which the local loss coefficient near endwall was chosen as the objective function.Compared with the traditional total pressure loss coefficient of the whole blade height,the local total pressure loss coefficient near endwall as the objective function increased the weight coefficient of the flow variation near the end region in the objective function.For the objective function,comparative studies were carried out between four different optimization schemes of total pressure loss coefficient of local blade height and the traditional total pressure loss coefficient of whole blade height.The optimization results showed that after the optimization of limited number of steps(400 steps),compared with the optimization scheme of total pressure loss coefficient of whole blade height as the objective function,the total pressure loss coefficient near the casing can be reduced more with the optimization scheme of total pressure loss coefficient of above 90% blade height as the objective function.The experimental results showed that for the optimization scheme of the total pressure loss coefficient above 90% blade height as the objective function,the total pressure loss coefficient within 10% blade height near the casing was reduced by 22.55% and the total pressure loss coefficient of the whole blade height was reduced by9.27%.It was better than the traditional optimization scheme with the whole blade height loss coefficient as the objective function,which the total pressure loss coefficient within 10% blade height near the casing decreased by 7.24% and the total pressure loss coefficient of the whole blade height decreased by 3.45%.In the fourth part,the endwall profiling positions were extended to simultaneous profiling of hub endwall and casing endwall.The optimization design of endwall profiling at design point,near stall point and at both design point and near stall point were carried out respectively.For the objective function of optimization,comparative studies were carried out with the optimization schemes of total pressure loss coefficient of whole blade height and local blade height near the casing and hub endwall under these three conditions.The optimization results of the schemes that under simultaneous design point and near stall point with the total pressure loss coefficient of the whole blade height and within10% blade height near the casing and hub endwall as the objective functions were experimentally studied.The experimental results showed that the optimization effect of the latter scheme was better than the former traditional one in reducing stator loss.The latter scheme reduced the total pressure loss coefficient of the whole blade height by 4.67% more at design point and 4.56% more at near stall point than the former scheme.The mechanism of non-axisymmetric endwall improving the flow near the end region was revealed by comparing the optimization results at design point and near stall point with prototype stator.By replacing the traditional total pressure loss coefficient of the whole blade height to the local total pressure loss coefficient near the casing and hub endwalls,the total pressure loss coefficient near endwalls and the whole blade height were both reduced to a greater extent,in a limited number of optimization steps(400 steps).The optimization speed was faster,and the optimization time was reduced to a certain extent,which was conducive to the engineering application of the non-axisymmetric endwall optimization design technology.Through these four parts of research,the blank of non-axisymmetric endwall technology in multi-stage axial-flow compressor is filled.The optimization design method of non-axisymmetric endwall for the embedded stator of multistage compressor is explored.By using the total pressure loss coefficient of local blade height near the endwalls as the objective function,the optimization time is reduced,which lays a foundation for the engineering application of this technology.