Application Of The Low-speed Similitude Modeling Principle In Highly Loaded Axial Compressor Design

The Design of highly loaded axial compressor is an important development trend and research direction of modern compressor.In the conventional design process of axial compressor,after the initial compressor scheme is obtained with the I-D design program,3-D numerical simulation will be conducted to validate its performance and help to optimize the compressor scheme.In the end,experiments will be performed with the optimized scheme,and based on the experimental data further update of the compressor blade will be taken to improve its performance.However,there is two unprecedented difficulties in the design of highly loaded compressor:On the one hand,the experimental test of the original compressor is meeting great challenges in material and processing technology for the blade due to the extremely high rotating speed,which will raise the cost and risk;On the other hand,high pressure ratio will lead to the decreasing of flow area,which will create great difficulties in flow field measurement.Therefore,once the designed highly loaded compressor didn't meet the design requirement according to the experiment data,then it is almost impossible to perform further improvement for the absence of detail flow field measurement.Thus,it is necessary obtain the flow field information in high speed compressor with the low speed analog modeling method.This method will greatly reduce the difficulty in measurement and also the cost and risk in experiment.In this paper,the principle of low speed analog modeling is studied to provide assistance for the design optimization of high load axial flow compressor.Though a lot of researches have been conducted both domestic and abroad,most of the studies are focused on the flow loss at design point.As a supplement,the key scientific problem of this paper is put forwards:How to ensure the similarity in flow stability between the high speed compressor and low speed model compressor with analog modeling method.Focused on the core scientific problem,series of research work has been carried out:firstly,a highly loaded axial compressor is designed and studied and the need and necessarity for the low speed analog method are brought up.Then similarity analysis is conducted based on tip leakage model and the similitude criterion for tip leakage flow is summarized.Aiming at providing experimental support,the Large Scale Low Speed Research Compressor test rig is designed and built.In the end,the low speed analog modeling method is applied to design the low speed model of the designed highly loaded compressor.The similarity of tip leakage flow in the two compressors is validated with both numerical and experimental method.The principle work of this paper is listed below:1.The highly loaded axial compressor design requirement is provide by Hannover University.During the study of the compressor design,1D aerodynamic design program is developed to obtain the initial compressor scheme.After the analysis of the flow field at design point,the design scheme is optimized.According to the simulation results,the design requirement at design speed is fulfilled.However,the stall margin at low operating speed doesn't meet the required operating line.The operating line at 60%of the design speed is selected as the modeling design target.2.Analysis is performed to clarify the key parameters to guarantee the similarity of high speed compressor and its low speed counterpart.Firstly,the tip leakage flow model is analysis for the spillage of the interface between tip leakage flow and the main flow(TLF/MF interface)is considered to be key factor that triggered the spike stall inception.Then Euler Equation and the velocity triangle at both inlet and outlet are anglicized to figure out how to ensure the similarity of pressure-rise coefficient line for all the operating points.3.Large Scale Low Speed Research Compressor test rig was designed and fabricated.The test rig has a lot of advantage over the regular test rigs,such as higher concentric degree,operation convenience,safety and reliability.Measurement of the flow field at rotor outlet is also performed with a dynamic probe.Flow structure and its relation with the unsteady phenomena at rotor outlet are anglicized and studied.The experimental data demonstrate that the test rig and its measurement method and fulfill the requirement of the research on detailed flow field.4.Low speed model compressor was designed with the analog modeling method.After the 2-D airfoils at different span-wise section were designed,actually the designer has some freedom on the choice of the geometry parameters to design the 3-D blade.Parameters such as aspect ratio,solidity and stacking mode are optimized to obtain the best low speed model scheme.Based on the numerical and experimental data,the low speed model compressor has a lot of similarity with the original high speed compressor on performance line,blade loading distribution and axial location of the TLF/MF interface.