Showing papers by "Itzhak Green published in 2001"

Numerical Formulation for the Dynamic Analysis of Spiral-Grooved Gas Face Seals

Abstract: A numerical formulation is presented for the dynamic analysis of spiral-grooved gas lubricated mechanical face seals with a flexibly mounted stator. Axial and angular modes of motion are considered. Both finite volume and finite element methods are employed for the spatial discretization of the unsteady, compressible form of the Reynolds equation. Self-adapting unwinding schemes are employed in both methods, making them suitable for situations when the compressibility number is high. Both the lubrication analysis and the kinetic analysis are arranged into a single state space form, which makes coupling the two analyses straightforward. The resulting set of equations is solved using a linear multistep ordinary differential equation solver. Examples of the transient response to static stator misalignment and rotor runout are given. Although a properly designed spiral grooved face seal provides good dynamic performance, it is shown that unacceptably large face separation can occur when large angle spiral grooves are employed together with a sealing dam. @DOI: 10.1115/1.1308015#

A Simultaneous Numerical Solution for the Lubrication and Dynamic Stability of Noncontacting Gas Face Seals

Abstract: A numerical solution is presented for the dynamic analysis of gas lubricated noncontacting mechanical face seals having a single grounded flexibly mounted stator. Seal dynamics is solved in axial and angular modes of motion. Both the Reynolds equation and the equations of motion are arranged into a single state space form, allowing the fluid film lubrication and the dynamics to be solved simultaneously. The resulting set of equations is solved using a high-order multistep ordinary differential equation solver, yielding a complete simulation for the seal dynamic behavior. Examples of seal motion are given in detailed transient responses. The stability threshold is investigated to gauge the influence of seal parameters such as inertia, speed, coning, and the direction of sealed pressure drops. The results show two modes of instability: (1) When the inertia effect is larger than a critical value, the natural response of the seal grows monotonically in a half-frequencywhirl mode. (2) When the seal coning is less than some critical value in an outside pressurized seal, the minimum film thickness diminishes because of hydrostatic instability, and face contact occurs. Conversely, an inside pressurized seal is shown to be hydrostatically stable and have a superior dynamic response at any coning. @DOI: 10.1115/1.1308020#

Study of the Tribological Behavior of a Thrust Washer Bearing

Abstract: This study addresses the mechanisms that distress a flat-faced thrust washer bearing system. This washer bearing system separates a helical gear and its carrier within a gearset. It was found that the bearing can experience distress by the combination of rotational speed, axial load, and the sequence and rate of their application. Distress is defined as a sudden rise in the real-time frictional torque and temperature. The various tests suggest the presence of hydrodynamic effects at certain rotational speeds and axial load combinations marked by decreases in the calculated effective coefficient of friction with decreases in velocity. In the tested cases, a distinct increase in the coefficient of friction occurs at the instant of distress. Presented at the 56th Annual Meeting Orlando, Florida May 20–24, 2001