Stability Threshold Velocity for a Hybrid Short Journal Bearing with the Injection Ports in the Symmetric Points

Abstract

Aims: Analytical determination of the eccentricity and attitude angle, rotordynamic coefficients (stiffness and damping), stability threshold velocity of the hybrid short journal bearing with the oil injection ports situated in symmetric points for ß= 7Π/4, 5Π/4, 3Π/4, Π/4. Analyzing the influence of external pressure allows to obtain some qualitative and quantitative behaviour characteristics of such bearing, which are of great importance to understand the process of pressurization when the injection port is placed in different points of the journal bearing. Also these results can be used at preliminary stages of pressurized bearing design for turbomachinery. The analytical results are validated by numerical calculation solving the Reynolds equation by finite difference method. Place and Duration of Study: Vibrations and Rotordynamics Lab. Department of Mechanic Engineer, IPN-SEPI-ESIME Building 5, 3er Floor, Zacatenco, Av. Wilfrido Massieu s/n, C.P. 07730, Mexico, D.F. México, between January 2012 and July 2012. Methodology: The well-known Reynolds equation for journal bearings is solved by means of the Ocvirk approximation for short bearing solution. The model of the spatial Dirac delta function δ(x) allows to analyze the influence of the external pressurization. Results: The analytical solution using the new model of punctual pressurization is very reliable since the results are sufficiently similar to those obtained by the numerical method. Several tables are calculated which allow finding given values of eccentricity due to pressurization. Conclusion: The journal dynamics shows that is better to locate the injection port of lubricant in ß= 7Π/4 in order to postpone the instability.