This paper deals with modeling of hole-pattern and honeycomb seals. These are frequently used as balance piston seals in high pressure centrifugal compressor applications as they have the potential to facilitate superior rotordynamic damping characteristics while providing good leakage control. On the other hand it is also well-established that the rotordynamic performance of hole-pattern and honeycomb seals is very sensitive to convergence and divergence in the streamwise direction. The ISOTSEAL bulk-flow code has shown difficulties in predicting the rotordynamic coefficients for convergent seal geometries or in cases with negative preswirl. This has led to increased interest in CFD-based analysis of seal dynamics. CFD-based models generally have less assumptions and are applicable for complex geometries or operating ranges not covered by bulk-flow codes. The CFD-based Instationary Perturbation Model (IPM) is utilized for the analysis of the hole-pattern and honeycomb seals. The rotordynamic forces are obtained by means of a time-dependent perturbation of the rotor position with respect to the stator. A sequence of perturbation frequencies is utilized to obtain the frequency dependence of the rotordynamic seal force coefficients. A strong effort has been put into validating the CFD-based perturbation modeling techniques against published experimental seal test data and the paper describes selected validation cases. A constant-clearance hole-pattern seal and a convergent honeycomb seal are analyzed and the results are compared to experimental results. The frequency dependence of the rotordynamic stiffness and damping characteristics of the seals is very well-captured for both types of seals.Finally, the IPM method was applied to a convergent hole-pattern seal to investigate the effects of eccentricity on the rotordynamic coefficients. The results are consistent with available experimental data.

The most recent development in centrifugal compressor technology is towards wet gas operating conditions. This means the centrifugal compressor has to manage a liquid phase which is varying between 0 to 3% Liquid Volume Fraction (LVF) according to the most widely agreed definition. The centrifugal compressor operation is challenged by the liquid presence with respect to all the main aspects (e.g. thermodynamics, material selection, thrust load) and especially from a rotordynamic viewpoint. The main test results of a centrifugal compressor tested in a special wet gas loop [1] show that wet gas compression (without an upstream separation) is a viable technology. In wet gas conditions the rotordynamic behavior could be impacted by the liquid presence both from a critical speed viewpoint and stability wise. Moreover the major rotordynamic results from the previous mentioned test campaign [2] show that both vibrations when crossing the rotor first critical speed and stability (tested through a magnetic exciter) are not critically affected by the liquid phase. Additionally it was found that the liquid may affect the vibration behavior by partially flooding the internal annular seals and causing a sort of forced excitation phenomenon. In order to better understand the wet gas test outcomes, the authors performed an extensive CFD analysis simulating all the different types of balance piston annular seals used (namely a Tooth on Stator Labyrinth Seal and a Pocket Damper Seal). They were simulated in both steady state and transient conditions and finally compared in terms of liquid management capability. CFD simulation after a proper tuning (especially in terms of LVF level) showed interesting results which are mostly consistent with the experimental outcome. The results also provide a physical explanation of the behavior of both seals, which was observed during testing.

The recent move towards subsea oil and gas production brings about a requirement to locate process equipment in deepwater installations. Furthermore, there is a drive towards omitting well stream separation functionality, as this adds complexity and cost to the subsea installation. This in turn leads to technical challenges for the subsea installed pumps and compressors that are now required to handle multiphase flow of varying gas to liquid ratios. This highlights the necessity for a strong research focus on multiphase flow impact on rotordynamic properties and thereby operational stability of the subsea installed rotating machinery. It is well known that careful design of turbomachinery seals, such as interstage and balance piston seals, is pivotal for the performance of pumps and compressors. Consequently, the ability to predict the complex interaction between fluid dynamics and rotordynamics within these seals is key. Numerical tools offering predictive capabilities for turbomachinery seals in multiphase flow are currently being developed and refined, however the lack of experimental data for multiphase seals renders benchmarking and validation impossible. To this end, the Technical University of Denmark and Lloyd’s Register Consulting are currently establishing a purpose built state of the art multiphase seal test facility, which is divided into three modules. Module I consists of a full scale Active Magnetic Bearing (AMB) based rotordynamic test bench. The internally designed custom AMBs are equipped with an embedded Hall sensor system enabling high-precision non-contact seal force quantification. Module II is a fully automatised calibration facility for the Hall sensor based force quantification system. Module III consists of the test seal housing assembly. This paper provides details on the design of the novel test facility and the calibration of the Hall sensor system employed to measure AMB forces. Calibration and validation results are presented, along with an uncertainty analysis on the force quantification capabilities.

This paper presents a first venture into quantifying stiffness and damping coefficients for turbomachinery seals in multiphase flow using Computational Fluid Dynamics (CFD). The study focusses on the simplest seal type: the smooth annular seal. The investigation is conducted for both wet-gas and bubbly flow regimes in which the primary phase is gas (air) and liquid (water), respectively. For the wet gas regime three different Liquid Volume Fraction (LVF) conditions are included in the study; 5%, 3% and 0%. Similarly for the bubbly flow regime three Gas Volume Fractions (GVF) conditions are included; 5%, 3% and 0%. An Eulerian-Eulerian modelling approach is taken, applying an inhomogeneous model, where the primary phase is treated as continuous and the secondary phase is included as dispersed. The Instationary Perturbation Method (IPM) is applied to identify the rotordynamic coefficients, in which the rotor is harmonically perturbed, and forces acting on the rotor are quantified through integration of the pressure and shear stresses. The perturbation is repeated for different frequencies to uncover any frequency dependence. The results presented in this paper are intended as an initial comparison basis for the experimental results to be obtained by applying the multiphase seal test facility currently in development, as part of a collaboration between Lloyd’s Register Consulting, the Technical University of Denmark, OneSubsea, TOTAL and Statoil.

In the petroleum industry, water-and-gas breakthrough in hydrocarbon reservoirs is a common issue that eventually leads to uneconomic production. To extend the economic production lifetime, inflow-control devices (ICDs) are designed to delay the water-and-gas breakthrough. Because the lifetime of a hydrocarbon reservoir commonly exceeds 20 years and it is a harsh environment, the reliability of the ICDs is vital. With computational fluid dynamics (CFD), an inclined nozzlebased ICD is characterized in terms of the Reynolds number, discharge coefficient, and geometric variations. The analysis shows that especially the nozzle edges affect the ICD flow characteristics. To apply the results, an equation for the discharge coefficient is proposed. The Lagrangian particle approach is used to further investigate the ICD. This allows for erosion modeling by injecting sand particles into the system. By altering the geometry and modeling several scenarios while analyzing the erosion in the nozzles and at the nozzle edges, an optimized design for incompressible media is found. With a filleted design and an erosion-resistant material, the mean erosion rate in the nozzles may be reduced by a factor of more than 2,500.