Research Of Dynamic Characteristics On Hydrodynamic Journal Bearing-Rotor System

The rotor dynamic characteristic is one of the concerning problems in the design of therotating machinery. The dynamic characteristics were researched for hydrodynamic journalbearing-rotor system in the paper which was a structure in a real project. The results providedreference for the use and improved design of certain large three-set mechanical system andpossessed important theoretical value and applied engineering meaning. The main researchedcontents and results of the paper were listed as follows:(1) The numerical solution was deduced for Reynolds equation. The pressure distribution ofthe journal bearings’ oil film was obtained making use of the solution program. The influence ofthe bearing’s dynamic characteristics was analyzed in detail about the bearing’s geometryparameters and working parameters. The results showed that the bearing’s dynamic characteristiccoefficients were greatly influenced when the clearance ratio was less than0.2. The dampingcoefficients respectively decreased rapidly and increased along with the increase of the clearanceratio and the eccentricity ratio as well as the aspect ratio.(2) The oil film thickness expression was deduced considering slope of the journal in thepaper, and the effect was studied for the slope angle and the deflection angle on oil filmdistribution and its resultant force. The results showed that the maximum value of the oil filmpressure offset to the bearing’s outboard because of the slope angle. The deflection angle did notmuch affect the oil film pressure, but it could change the distribution of the oil film pressure.(3) The dynamic model was researched with numerical and experimental analysis forhydrodynamic journal bearing-rotor system. The results showed that the critical speeds increasedalong with the supporting stiffness, and the calculated results accorded with the experimentalresults. The rotor’s double harmonic frequency appeared along with the increase of the unbalanceconsidering the nonlinearity characteristics of the bearing’s film pressure. The model rotorappeared periodic motion--doubling periodic motion--large periodic, large amplitude and1/2single frequency periodic motion as the speed increased because of the influence of thenonlinearity characteristics of the bearing’s film pressure. The stability of the rotor system couldbe improved by changing the radius clearance and the aspect ratio.(4) The characteristics of journal bearings were analyzed with the theory and method ofhydrodynamic lubrication for the three-set mechanical system, and the influence were obtainedabout lubricating oil temperature, journal speed and oil supply pressure on bearing’s dynamiccharacteristics. The critical speeds of the three-set mechanical system were separately calculated with the both methods of the transfer matrix and the FEM considering the change of thecharacteristics of the hydrodynamic journal bearing along with the speed. The results showed thatthe results of the both methods were consistent. The critical speeds safety margins were notenough for the fan and the turbo rotor, while the critical speeds of the motor rotor satisfied thedesign request, and the dynamic characteristics of rotors could be improved with changing kindsof lubricating oil. The research contents provided helpful references for the engineeringapplication of the three-set mechanical system in the paper.