| Since the invention of gas turbine,it has quickly taken over the engine market due to its high power,small size,and low weight.Gas turbines designed for marine propulsion systems have been developed by various countries since the 1960 s.In the marine environment,the air is mixed with a large amount of salt spray particles.Even with high-performance intake filtration systems,some small particles still enter the gas turbine.Long-term operation in the marine environment can cause an increase in roughness on the surface of the compressor blades.Studies have shown that an increase in roughness on the compressor blade surface can cause a certain degree of performance degradation,affecting the safe and stable operation of the gas turbine.Due to the high cost of compressor experimental research and the difficulty of measurement,domestic and foreign research work mainly uses numerical simulation as a research method.Although the numerical model has corrected the flow field near the rough wall surface,there is still controversy over the relationship between the arithmetic average roughness Ra and the equivalent sand grain diameter hs in the correction model.This article will use a combination of experimental measurement and numerical simulation methods to study the influence of roughness on the wall boundary layer,and then study the influence of roughness on the performance of compressor blades,and finally summarize the influence of roughness on the performance degradation of axial flow compressors using numerical simulation methods.First,a low-speed flat wind tunnel experimental platform was designed,and a flat experimental piece was used as the research object.Under four different incoming Reynolds number conditions,the logarithmic velocity zone flow field in the boundary layer was measured.Sandpaper was used to simulate the roughness of the flat plate surface.Combined with existing boundary layer theory,the experimental measurement data was analyzed to obtain the non-dimensional velocity distribution of the boundary layer in the logarithmic zone under different roughness conditions.By combining the curve changes under multiple roughness conditions,the relationship between the geometric arithmetic average roughness and the equivalent sand grain roughness was finally obtained as hs=6.825 Ra.Numerical simulation methods were used to simulate the flat experimental piece,and the numerical calculation results were verified to fit well with the experimental values.Select a compressor blade model and design a wind tunnel measurement experiment platform for compressor blade.Use sandpaper to simulate the relative roughness(Ra/c)of the blade surface,which are 1.46×10-3 and 2.43×10-3 respectively.Measure the surface pressure distribution of the blade before and after roughness and the total pressure loss and velocity distribution at the outlet of the blade.The experimental results show that the overall total pressure loss of the blade increases significantly after roughness,and the total pressure loss coefficient at the outlet of the blade under the two roughness conditions increases by 35% and 75% respectively.At the same time,establish the same physical model as the blade wind tunnel experiment,use the SST k-ω turbulence model to numerically simulate the blade model,and turn on the roughness correction model to adapt to the situation where the surface has roughness.When calculating the rough blade,use the relationship between Ra and hs obtained in the flat plate experiment study.By comparing the computational results with the experimental results of the cascade,the feasibility of the numerical simulation method is demonstrated.Based on this,further analysis of the numerical simulation results of the cascade is carried out,and the calculation conditions of the cascade under different inflow angles,Reynolds numbers,and surface roughness are added.The sensitivity of the rough cascade to inflow angle and Reynolds number is studied,and the advantage of numerical simulation is used to analyze the flow field structure inside the cascade.The study shows that there is a gradient interval for the effect of roughness on the loss coefficient of the compressor cascade.Before the compressor cascade is completely rough,the overall loss coefficient of the cascade increases by 5% for every increase of 1×10-4 in relative roughness.When the cascade is completely rough,the loss coefficient at the outlet of the cascade increases by 15% for every increase of 1×10-4 in relative roughness.The sensitivity of the loss coefficient of the rough cascade to the inflow Reynolds number increases after the blade is roughened,while the sensitivity to the inflow angle decreases.After completing the relevant research work in the cascade,the prediction of the impact of roughness on compressor performance degradation is carried out.NASA Stage35 single-stage axial compressor is selected as the research object,and the same numerical simulation method as the cascade is used to simulate the compressor under different roughness blade conditions.The results show that when the roughness of the moving blade surface of the compressor reaches20μm,the total pressure ratio and efficiency of the compressor decrease by 1.66% and 1.43%,respectively.When the roughness is greater than 20μm,for every increase of 10μm in the roughness of the moving blade,the pressure ratio and efficiency of the compressor decrease by1.64% and 1.81%,respectively.Roughness can also cause a decline in the stability margin of the axial compressor.For every increase of 10μm in roughness,the pressure ratio stability margin decreases by about 1%,while the flow rate stability margin increases by 2%.However,the blocking flow rate of the compressor decreases at the same time.Develop a performance prediction model for Stage 35 compressor,incorporating a correction factor for the impact of surface roughness on compressor performance,and establish a model for predicting the degradation of compressor performance due to surface roughness. |
