The influence of 3-DOF film thickness disturbance on transient performance of typical spiral groove dry gas seals

Purpose The purpose of this paper is to investigate the influence rule and mechanism of three degrees of freedom film thickness disturbance on the transient performance of spiral groove, upstream pumping spiral groove dry gas seal (UP-SDGS) and double-row spiral groove dry gas seal (DR-SDGS). Design/methodology/approach The transient performance of spiral groove, UP-SDGS and DR-SDGS are obtained by solving the transient Reynolds equation under different axial and angular disturbance coefficients. The transient and steady performance of the above-mentioned DGSs are compared and analyzed. Findings The film thickness disturbance has a remarkable impact on the sealing performance of DGS with different structures and the calculation deviations of the leakage rate of the UP-DGS will increase significantly if the film thickness disturbance is ignored. The axial and angular disturbance jointly affect the film thickness distribution of DGS, but there is no significant interaction between them on the transient sealing performance. Originality/value The influence mechanism of axial disturbance and angular disturbance on the transient performance of typical SDGSs behavior has been explained by theory. Considering small and large disturbance, the interaction between axial disturbance and angular disturbance on the transient performance have been studied.

Predictions of the thermo elastic deformation of dry gas seal rings in the hydrodynamic lubrication regime

Dry gas seals represent a significant advancement in turbo machinery due to their ability to handle high pressures and speeds without the use of external sealing fluids, such as oil or water, thus reducing contamination and increasing reliability. Despite their widespread use, internal working mechanisms are not fully understood to date, in particular regarding fluid film thickness prediction, which is an essential component of the seal design. The axial deflection of the rotating and stationary rings in a dry gas seal affects the development of the fluid film formed between the ring faces of the seal, influencing the performance of the seal during its operation, as well as leakage of the seal when it is at rest. The hydrodynamic and hydrostatic pressure fields of the fluid film, together with temperature gradients in the rings, induce axial deflection of these components. This in turn modifies the pressure field developed in the film. This paper focuses on establishing a methodology to couple the deformation field and the dynamic behavior of the fluid film (pressure and temperature fields) through numerical computations. Analytical relationships are employed to obtain the thermo-elastic deflection of the seal rings in the axial direction and this distortion is used in the numerical methodology to accelerate the prediction of the seal behavior. The coupled seal ring-fluid film dynamic system with 11° and 15° spiral angle is stable because the axial deflection calculated from numerical analysis produces a converging radial taper in the direction of the flow (producing a net opening force). An important result of this work is that the predicted magnitude of the axial deflection (as a result of pressure and temperature effects) under thermal and pressure loads on the stationary and rotating rings is smaller but of the same order of magnitude as the fluid film thickness.

Experimental Studies on Dry Gas Seals With Time-Resolved Film Thickness Measurements

Dry gas lubricated non-contacting mechanical seals (DGS) are acknowledged as the sophisticated shaft end sealing solution which is most commonly found in turbo-compressors. Especially under demanding conditions where high speed is combined with high pressure, DGS becomes the preferred choice over other sealing alternatives. A reliable operation of DGS, due to the non-contact running between its rotating and stationary rings, is secured by the gas film in the region of a few microns in thickness. This paper presents the measurement method of obtaining the thickness of the running gap in two radial positions, namely the inner and outer diameter of the sealing gap, by integrating the proximity sensors in the stationary ring. The experimental investigations concerning film thicknesses, pressure distributions in the gas film and axial vibrations are carried out in an industry DGS up to 50 bar and 10,000 rpm, whereby a good insight into the dynamic behaviour of the sealing gap is provided. The results demonstrate the practicability of obtaining the gas film parameters in a grooved gas seal, bridging the gap between theory and practice. In combination with the experimental work presented in this paper, the numerical model for simulating the seal performance programmed in MATLAB is compared and validated. The comparisons for various operating conditions and groove profiles are discussed with the focus lying on the hydrodynamic effect in the gas film.

Leakage and Rotordynamic Characteristics for Three Types of Annular Gas Seals Operating in Supercritical CO2 Turbomachinery

This paper presents a comprehensive assessment and comparison on the leakage and rotordynamic performance of three types of annular gas seals for application in a 14 MW supercritical CO2 turbine. These three seals represent the main seal types used in high-speed rotating machines at the balance piston location in efforts to limit internal leakage flow and achieve rotordynamic stability, including a labyrinth seal (LABY), a fully-partitioned pocket damper seal (FPDS), and a hole-pattern seal (HPS). These three seals were designed to have the same sealing clearance and similar axial lengths. To enhance the seal net damping capability at high inlet preswirl condition, a straight swirl brake also was designed and employed at seal entrance for each type seal to reduce the seal inlet pre-swirl velocity. Numerical results of leakage flow rates, rotordynamic force coefficients, cavity dynamic pressure and swirl velocity developments were analyzed and compared for three seal designs at high positive inlet preswirl (in the direction of shaft rotation), using a proposed transient CFD-based perturbation method based on the multiple-frequency elliptical-orbit rotor whirling model and the mesh deformation technique. To take into account of real gas effect with high accuracy, a table look-up procedure based on the NIST database was implemented, using an in-house code, for the fluid properties of CO2 in both supercritical and subcritical conditions.