考虑表面粗糙度的干气密封边界膜滑移效应分析
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摘要
为了研究随机粗糙表面上的滑移流效应,针对符合高斯分布的粗糙度表面,考虑其影响对一阶滑移模型进行修正,建立适用于随机粗糙表面的有效滑移长度模型;建立流体润滑方程,采用数值分析方法对其进行计算,研究粗糙峰间距、粗糙度均方根对滑移流以及螺旋槽干气密封的密封性能的影响。研究结果表明:气体分子平均自由程较小、粗糙峰间距较小或者粗糙度均方根较大的情况下,密封端面更容易发生负滑移现象;在微尺度条件下,负滑移有助于提高密封的端面开启力和运行稳定性;滑移流对气膜刚度的影响最大,气膜承载力次之,泄漏率最小且可以忽略不计。
In order to have a better understanding of boundary slip on random rough surface,one-order slip model was modified by considering the effect of roughness following a Gaussian distribution on boundary slip,and effective slip length model available for random roughness was established. Reynolds equation considering boundary slip on random roughness was derived to find out the effect of roughness peak spacing and root mean square roughness( RMS Roughness) on boundary slip and sealing performance of spiral groove dry gas seal by numerical analysis way. The results show that the narrower the gas molecular free path and roughness peak spacing is,the more likely negative slip occurs; the smaller RMS roughness is,the more likely positive slip occurs. Under micro-scale conditions,negative slip can help increase open force and running stability. Comparing to film stiffness,the effect of slip on bearing capacity is less evident,while the effect on leakage can be ignored.
In order to have a better understanding of boundary slip on random rough surface,one-order slip model was modified by considering the effect of roughness following a Gaussian distribution on boundary slip,and effective slip length model available for random roughness was established. Reynolds equation considering boundary slip on random roughness was derived to find out the effect of roughness peak spacing and root mean square roughness( RMS Roughness) on boundary slip and sealing performance of spiral groove dry gas seal by numerical analysis way. The results show that the narrower the gas molecular free path and roughness peak spacing is,the more likely negative slip occurs; the smaller RMS roughness is,the more likely positive slip occurs. Under micro-scale conditions,negative slip can help increase open force and running stability. Comparing to film stiffness,the effect of slip on bearing capacity is less evident,while the effect on leakage can be ignored.
引文
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[14]PANZER P,EINZEL D,LIU M.Fluid slip at walls with mesoscopic surface roughness[J].Physica B,1990,165(1):555-556.
[15]尹晓妮,彭旭东.考虑滑移流条件下干式气体端面密封的有限元分析[J].润滑与密封,2006,4:55-59.YIN X N,PENG X D.Finite element analysis of a dry-gas seal under slip flow conditions[J].Lubrication Engineering,2006,4:55-59.
[2]彭旭东,李纪云,盛颂恩,等.表面粗糙度对螺旋槽干式气体端面密封性能预测与结构优化的影响[J].摩擦学学报,2007,27(6):567-572.PENG X D,LI J Y,SHENG S E,et al.Effect of surface roughness on performance prediction and geometric optimization of a spiral-groove face seal[J].Tribology,2007,27(6):567-572.
[3]MAKINO T,MOROHOSHI S,TANIGUCHI S.Application of average flow model to thin film gas lubrication[J].Journal of Tribology,1993,115(1):185-190.
[4]TRIPP J H.Surface roughness effects in hydrodynamic lubrication:the flow factor method[J].Journal of Lubrication Technology,1983,105(3):458-463.
[5]LI W L,WENG C I,HWANG C C.Effects of roughness orientations on thin film lubrication of a magnetic recording system[J].Journal of Physics D:Applied Physics,1995,28(6):1011-1021.
[6]CAO B Y,CHEN M,GUO Z Y.Effect of surface roughness on gas flow in microchannels by molecular dynamics simulation[J].International Journal of Engineering Science,2006,44(13):927-937.
[7]KUNERT C,HARTING J.Roughness induced boundary slip in microchannel flows[J].Physical Review Letters,2007,99(0,017):1-4.
[8]GREENWOOD T A,TRIPP J H.The contact of two nominally flat rough surfaces[J].Proceedings of the Institution of Mechanical Engineers,1970,185:625-634.
[9]ETSION I,FRONT I.A model for static sealing performance of end face seals[J].Tribology Transactions,1994,37(1):111-125.
[10]EINZEL D,PANZER P,LIU M.Boundary condition for fluid flow:curved or rough surfaces[J].Physical Review Letters,1990,64(19):2269-2272.
[11]BURGDORFER A.The influence of the molecular mean free path on the performance of hydrodynamic gas lubricated bearings[J].ASME Journal of Basic Engineering,1959,81(2):94-100.
[12]POLYCARPOU A A,ETSION I.A model for the static sealing performance of compliant metallic gas seals including surface roughness and rarefaction effects[J].Tribology Transactions,2000,43(2):237-244.
[13]PONOMAREV I V,MEYEROVICH A E.Surface roughness and effective stick-slip motion[J].Physical Review E,2003,67(2):1-14.
[14]PANZER P,EINZEL D,LIU M.Fluid slip at walls with mesoscopic surface roughness[J].Physica B,1990,165(1):555-556.
[15]尹晓妮,彭旭东.考虑滑移流条件下干式气体端面密封的有限元分析[J].润滑与密封,2006,4:55-59.YIN X N,PENG X D.Finite element analysis of a dry-gas seal under slip flow conditions[J].Lubrication Engineering,2006,4:55-59.