Effect Of Roughness On Performance Degradation Of Compressor Cascade

During the operation of gas turbine,due to the influence of environment,the blade is affected by corrosion,scaling or erosion,resulting in the increase of surface roughness.The traditional roughness research methods include wall function method and changing blade profile method.The research method is simple,but it does not accord with the actual blade roughness distribution.Based on the traditional research methods and aiming at the physical characteristics of random distribution of roughness in engineering practice,this paper proposes a geometric deformation method of random distribution of rough surface,which makes up for the short plate uniformly distributed on rough surface by changing blade profile method.In this paper,DCA cascade is taken as the research object,and its numerical simulation is carried out to study the effects of incoming Reynolds number,incoming angle of attack and roughness distribution on cascade performance.The variation laws of cascade performance and internal flow field under different working conditions and different roughness are summarized.The main research contents of this paper are as follows:1.According to the geometric parameters,the double arc cascade model and watershed are established.Compared with the experimental values,the optimal grid number is selected,and it is found that the SST Turbulence model is the closest to the experimental values.Then the flow field inside the prototype cascade(k~+=0)is analyzed.2.The traditional method of roughness simulation is introduced.And the traditional research method is improved from the perspective of preserving the actual morphology of the blade surface roughness and the randomness of the rough distribution,which is called the geometric deformation method.The performance parameters and flow field changes calculated by wall function method are compared and analyzed.The results show that the wall function method always overestimates the performance parameters,especially at low Reynolds number.3.Based on the geometric deformation method,the variation law of cascade performance is studied,and four schemes are designed to explore the effects of Reynolds number,angle of attack,rough position and rough magnitude on cascade performance from the aspects:total pressure loss coefficient,wake loss coefficient,lift coefficient,static pressure coefficient,isentropic Mach number and outlet flow angle The flow characteristics are analyzed from the aspects of wake distribution and separated vortex.The results show that the cascade roughness has a great influence on the cascade performance at low Reynolds number;When the roughness is large,the range of attack angle of cascade under stable condition will be reduced.4.In order to further explore the influence of roughness on the internal flow field of cascade,the large eddy simulation method is used to simulate the unsteady condition.The distributions of pressure,velocity and vorticity under three different roughness degrees of cascade(k~+=0,k~+=40 and k~+=186)are studied.Compared with the traditional roughness simulation methods,the random number method used in this paper to change the blade profile to simulate the blade roughness can maximize the real geometric state of the rough cascade,and the numerical simulation results are closer to the real situation,but at the cost of a sharp increase in the number of grids.The calculation results show that compared with the results calculated by the wall function method,it is found that the parameters at the middle and rear of the cascade suction surface vary greatly at low Reynolds number,especially the wake distribution when the k~+value is large.It can be seen that the method of treating blade surface roughness by geometric deformation method is feasible and operable.