| The instantaneous changes of the working conditions have serious effects on the stability of the mechanical seal system during the actual operation.Currently,the performance analyses of the non-contacting mechanical seal have been mainly focused on the steady or dynamic state,seldom involved the transient behavior of fluid seal.In view of the above mentioned situation,taking upstream mechanical seal as object,the theoretical research,numerical simulation and experimental research methods are used to study the transient behavior of the seal under the transient startup,variable condition and disturbance environment.Specific works and conclusions are described as follows.Firstly,a three-dimensional model of sealing clearance was established based on MATLAB.Numerical analysis of lubrication characteristics in liquid film seals during transient start-up was established.The dynamic lubrication response in axial modes of motion was obtained in a coupled analysis where the average Reynolds equation contains contact factor and JFO cavitation boundary,asperity contact model and dynamic motion were solved simultaneously.The variation law of friction coefficient under different working condition parameters and structure parameters during starting process were studied.Secondly,SOR iteration was used to solve fluid film pressure distribution.Further coupled solved Reynolds equation considering JFO cavitation boundary and transient dynamic equations.The influence of continuous change of working conditions on transient characteristics was analyzed.Then the dynamic model of vibration and impact of liquid film seals were established in this paper.The influence of different dynamic parameters and the response law of pressure and speed variation on the stability and impact phenomenon of sealing system were studied.The change of time history diagram,phase trajectory and contact force were obtained.Ultimately,a mechanical seal test device was designed to study the sealing transient performance of various structural parameters during the transient changes operating conditions.The conclusions are as follows: squeeze effect of liquid film during transient change of pressure has more significant influence on sealing performance than speed change.Instantaneous change of pressure easily leads to the axial velocity oscillation of stator ring.The critical moment of lubricant transform has a mutation of axial speed.The liquid film thickness and leakage increase significantly when the end face enters the hydrodynamic lubrication regime.The smaller ramp rate could achieve liquid lubricated at low speed.Higher outer pressure or lower inner pressure is beneficial to the change of lubrication state.For the best separation ability of seal face,selecting parameters as follows: spiral angle within the range of 16~24°,groove depth 5~7μm,groove number 20~24 and groove width ratio 2/3~5/6.The vibration frequency of the film thickness is significantly larger than that of the full film lubricated regime when asperity contact occurs.Contact forces occur repeatedly between sliding surface when the speed ramps from 5000 rpm to 500 rpm.The impact force and shock frequency are continuously enhanced with the increase of the pressure outer diameter.There is a larger film thickness mutation at 2.5s and the step increases after 12 s during start up when the number of grooves is 24.Similarly,when the number of grooves is 12,the sudden change of the film thickness occurs at 3s,as well as an obvious step in 15 s.Compared with the increase of outer pressure,the change of film pressure on the surface tends to be more gentle and less of the amplitude reduction during the decrease of outer pressure. |
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