Computational investigation of fluid injection applications for the gas labyrinth seal

A variety of injection applications for the labyrinth seal have been successfully used for decades in field operations resolving many practical problems. However, there is a continuing void of understanding and design information available concerning gas labyrinth seals with a buffer-gas injection and with shunt injection. This void results in two problems: (a) unnecessarily high injection flow rates reduce the machine efficiency and (b) insufficient injection flow rate contaminates the process gas (for the buffer-gas labyrinth seal) or allows rotor instability (for the shunt injection).; For buffer-gas labyrinth seals, a 2-Dimensional, axisymmetric, CFD (finite volume) code was extended to compute oil vapor leakage for a wide range of bearing labyrinth geometries. The transport equation for the mass fraction of oil vapor was incorporated into the previous, standard k-ϵ turbulence model. The oil vapor transport characteristics are classified as flooded and non-flooded cases according to their source of oil vapor contaminant. For flooded cases, the geometry effects are investigated and discussed to minimize oil vapor transport. For non-flooded cases, a critical injection pressure was evaluated by extrapolating from the new leakage-pressure-drop computed results to obtain the minimum injection pressure that will prevent oil contaminant from entering the mainstream gas for a given set of pressures.; For gas labyrinth seals with a shunt injection, the zeroth- and the first-order codes were extended to investigate the effect of shunt injection on the rotordynamic characteristics. The relationship among the zeroth- and first-order flow quantities and rotordynamic coefficients is analyzed and presented. In addition, a multiple-domain technique was successfully implemented and used to compute shunt injection gas labyrinth seals and High-Low seals.; Important improved cause-and-effect understandings are presented and analyzed. The information obtained from the current investigation provides a more clear understanding of the injection characteristics and gives useful and practical design information of buffer-gas labyrinth seals and shunt injection gas labyrinth seals. This information should help to increase the machine efficiency of buffered oil labyrinths and the rotordynamic stability of shunt injection labyrinths.