A Computational Fluid Dynamics/Bulk-Flow Hybrid Method for Determining Rotordynamic Coefficients of Annular Gas Seals

Migliorini, Patrick J.; Untăroiu, Alexandrina; Wood, Houston G.; Allaire, Paul E.

doi:10.1115/1.4006407

Cited by 34 publications

(13 citation statements)

References 16 publications

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“…In the steady-state condition, the differential terms in Eqs. (5) and (6) are zero and the exchange flow rate between control volume 1 and control volume 2, qri, is also zero. Accordingly, in the steady-state condition, the following equations hold:…”

Section: Damper Seal Rotordynamic Calculation Methodsmentioning

confidence: 98%

“…However, the use of CFD analysis requires a time-intensive series of proc esses that includes modeling, computation, and postprocessing, so CFD analysis is not suited to single-product designs such as cen trifugal compressor seals. As a method for reducing the computa tion time, Migliorini proposed a hybrid method that combines CFD analysis and bulk flow analysis [5].…”

Section: Introductionmentioning

confidence: 99%

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Development of Scallop Cut Type Damper Seal for Centrifugal Compressors

Takahashi

Miura

Narita

et al. 2014

Journal of Engineering for Gas Turbines and Power

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This paper deals with a new type of damper seal developed for a high-pressure centrifu gal compressor. Honeycomb seals and hole pattern seals are popularly used as damper seals and provide superior rotordynamic damping characteristics. Honeycomb seals are expensive because the manufacturing process is complex. Hole pattern seals are easier to manufacture, but they are still expensive. Use of a scallop pattern is one way to reduce manufacturing cost and time. A new sea! that has a scallop pattern and small teeth on the stator surface is proposed. This pattern is cut on the stator surface using a disk type tool. To estimate the rotordynamic coefficients of this new seal, a bulk flow model code that is based on a two-control-volume model developed by Matsuda for labyrinth seals was newly developed. This model uses the Hirs model for the viscous shear stresses. The fric tion factor coefficients for the rotor surface, the stator surface, and the surface between the two-control-volumes were determined by computational fluid dynamics (CFD) steady analysis. The rotordynamic coefficients can also be obtained by using CFD perturbation analysis. The high accuracy of the bulk flow model was demonstrated by comparing its results with CFD perturbation analysis results. In the perturbation analysis, the whirling motion was treated as a steady-state problem by using a rotating frame of reference. For the damper seal, the rotor surface and its neighboring region were treated with a rotating frame of reference and the neighboring region of the stator was treated with a stationary frame of reference. The damping property of the new seal was evaluated by conducting rotor stability tests using a high-pressure compressor with an electromagnetic exciter. The new seal equipped with swirl brakes was used for the balance piston of the compres sor. Stability was evaluated by exciting the rotor during operation and identifying the eigenvalues of the rotor. The experimental results showed that the new seal increases damping. Comparison of the damping effect with calculations based on the bulk flow analysis showed good agreement.

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Section: Damper Seal Rotordynamic Calculation Methodsmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Development of Scallop Cut Type Damper Seal for Centrifugal Compressors

Takahashi

Miura

Narita

et al. 2014

Journal of Engineering for Gas Turbines and Power

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“…The stator wall is specified as a counter-rotating wall with no slip smooth boundary condition. The k-s turbulence model is adopted in conjunction with a scalable wall function [10]. A residual convergence criterion RMS of 1 x 10 s is speci fied for the CFD simulation.…”

Section: Cfd Base Model and Validationmentioning

confidence: 99%

Hole-Pattern Seals Performance Evaluation Using Computational Fluid Dynamics and Design of Experiment Techniques

Untăroiu

Cheng

Migliorini

et al. 2014

Journal of Engineering for Gas Turbines and Power

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A main goal o f noncontacting mechanical seals is to provide minimal leakage during oper ation. This may be achieved by specifying a small clearance between the mating faces that is just enough to avoid rubbing contact while allowing some tolerable leakage. The amount of leakage flow is reduced through the acceleration and deceleration o f the fluid through a tortuous path, so the sealing performance depends on the geometric characteristics o f the leakage path. This study focuses on annular hole-pattern seals, which are noncontacting mechanical seals commonly used in high pressure compressors. A design o f experiments (DOE) approach is used to investigate the effects o f various geometric variables on the leakage rate o f a hole-pattern seal during normal operating conditions. The design space, defined by the ranges o f hole diameter, hole depth, axial space between holes and number o f holes in circumferential direction, is discretized using the simple random sampling method. Then, steady-state computational fluid dynamics (CFD) simulations are performed at each design point to evaluate seal performance. To better understand the sensitivity o f the hole-pattern seal leakage rate with respect to design variables selected, response surfa ces are built through its values at design points using quadratic polynomial fitting. The results show that the optimal solution had a better leakage control ability over the base model design. It is believed that the results o f this study will assist in improving the design o f annular hole-pattern seals.

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“…Bulk flow methods are employed to predict leakage and rotordynamic properties for many different types of annular seals (Nordmann & Weiser, 1991;Williams & Flack, 1998;Migliorini, Untaroiu, & Allaire, 2012). This method involves dividing the seal domain into a few control volumes (typically less than four) and solving simplified versions of the momentum, continuity, and energy equations.…”

Section: Bulk Flow Methodsmentioning

confidence: 99%

Computational Porous Media Modeling of a Brush Seal for Incompressible and Slightly Compressible Flow

Gresham¹

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Annular seals are critical to the efficient operation of turbomachinery under increasingly high pressure loadings. Brush seals employ rows of bristles to close the gap between the rotor and the stator in rotating machinery. They typically handle larger pressure differentials and have demonstrated lower leakage than comparable labyrinth seals. However, an understanding of the complex nature of the flow within these seals is limited. This is primarily due to the difficulty associated with modeling the flow through the bristle pack.Traditionally, the performance modeling of annular seals has been accomplished by the use of bulk flow theory. This method is relatively simple to implement but can be problematic due to the fundamental assumptions required to reduce the governing equations to a solvable form. More recent studies have used full three-dimensional computational fluid dynamics models and finite element models to simulate the behavior of the bristles and their influence on the flow through the seal. This method typically provides more information than is necessary for standard design and analysis problems faced by engineers in the turbomachinery industry. Simulations of this type also require a great deal of time and knowledge from the user in order to be of any use and are very computationally expensive. Porous media modeling techniques have also proven effective, but their application has remained limited due to the uncertainty of how to estimate the permeability terms and a lack of a simple computer code appropriate for the problem.In this thesis, a new approach is presented using a simplified porous media-based model. The governing equations are formulated in terms of pressure distribution and then discretized using finite differences. An algorithm is developed to model situations of incompressible flow as well as compressible flow under isothermal conditions. The code is then analyzed to demonstrate its performance capabilities and utility for modeling flow through a standard brush seal. Properties of the numerical scheme are demonstrated and potential limitations are addressed.iii

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A Computational Fluid Dynamics/Bulk-Flow Hybrid Method for Determining Rotordynamic Coefficients of Annular Gas Seals

Cited by 34 publications

References 16 publications

Development of Scallop Cut Type Damper Seal for Centrifugal Compressors

Development of Scallop Cut Type Damper Seal for Centrifugal Compressors

Hole-Pattern Seals Performance Evaluation Using Computational Fluid Dynamics and Design of Experiment Techniques

Computational Porous Media Modeling of a Brush Seal for Incompressible and Slightly Compressible Flow

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