Predicted Effects of Shunt Injection on the Rotordynamics of Gas Labyrinth Seals

2002 ◽  
Vol 125 (1) ◽  
pp. 167-174 ◽  
Author(s):  
N. Kim ◽  
S.-Y. Park ◽  
D. L. Rhode
Keyword(s):  
High Pressure ◽  
Control Volume ◽  
Injection Pressure ◽  
Labyrinth Seal ◽  
Bulk Flow ◽  
Labyrinth Seals ◽  
Flow Perturbation ◽  
Flow Models ◽  
Primary Advantage ◽  
Control Volume Approach

A recent CFD perturbation model for turbomachinery seal rotordynamics was extended for labyrinth shunt injection with an arbitrarily high pressure gas. A large number of measured cases with labyrinth injection pressure at approximately 13.8 bars (200 psi) were computed and compared with measurements. The drastically reduced (negative) cross-coupled stiffness, which is the primary advantage from the use of shunt injection in gas labyrinth seal applications, was well predicted. The agreement with measurements for k, C, and Ceff was within about 40%, 60% and 10%, respectively. In addition, it was found that moving the injection toward the high pressure end of the seal gives k, C, and Ceff values that are rotordynamically only slightly more stabilizing. Further, the radial distributions of the flow perturbation quantities give support to the two-control volume approach for developing bulk-flow models for labyrinth seal rotordynamics.

Predicted Effects of Shunt Injection on the Rotordynamics of Gas Labyrinth Seals

2001 ◽  
Author(s):  
Namhyo Kim ◽  
Sung-Young Park ◽  
David L. Rhode
Keyword(s):  
High Pressure ◽  
Control Volume ◽  
Injection Pressure ◽  
Labyrinth Seal ◽  
Bulk Flow ◽  
Labyrinth Seals ◽  
Flow Perturbation ◽  
Flow Models ◽  
Primary Advantage ◽  
Control Volume Approach

A recent CFD-perturbation model for turbomachinery seal rotordynamics was extended for labyrinth shunt injection with an arbitrarily high pressure gas. A large number of measured cases with labyrinth injection pressure at approximately 13.8 bars (200 psi) were computed and compared with measurements. The drastically reduced (negative) cross-coupled stiffness, which is the primary advantage from the use of shunt injection in gas labyrinth seal applications, was well predicted. The agreement with measurements for k, C, and Ceff was within about 40 percent, 60 percent and 10 percent, respectively. In addition, it was found that moving the injection toward the high pressure end of the seal gives k, C and Ceff values that are rotordynamically only slightly more stabilizing. Further, the radial distributions of the flow perturbation quantities give support to the two-control volume approach for developing bulk-flow models for labyrinth seal rotordynamics.

Calibration of a Design Tool for Dynamic Characteristics of Gas Labyrinth Seals

2016 ◽  
Author(s):  
R. Gordon Kirk ◽  
Wen Jeng Chen
Keyword(s):  
High Pressure ◽  
Dynamic Characteristics ◽  
Critical Path ◽  
Flow Analysis ◽  
Labyrinth Seal ◽  
Design Tool ◽  
Bulk Flow ◽  
System Stability ◽  
Prior Work ◽  
Labyrinth Seals

The analysis of all critical path high pressure machinery must include the account of the influence of the gas labyrinth seals. This paper reviews the prior work on labyrinth seal analysis starting in the 1980’s. The discussion gives a summary of the calibration of the bulk flow analysis to CFD results for a number of conditions. The calibration process was conducted over the last decade and the current paper presents the key results needed to justify the use of this bulk flow analysis for design of machinery with bladed labyrinth seals. A new design tool is discussed with illustrations of the type of seals that can be studied. The dynamic characteristics calculated using the labyrinth seal program can be used in rotordynamic analysis programs to predict the change in system stability produced by the gas labyrinth seals.

Impact of Frequency Dependence of Gas Labyrinth Seal Rotordynamic Coefficients on Centrifugal Compressor Stability

2010 ◽  
Author(s):  
Giuseppe Vannini ◽  
Manish R. Thorat ◽  
Dara W. Childs ◽  
Mirko Libraschi
Keyword(s):  
Molecular Weight ◽  
Numerical Model ◽  
Control Volume ◽  
Labyrinth Seal ◽  
Labyrinth Seals ◽  
Frequency Dependent ◽  
Rotordynamic Coefficients ◽  
Frequency Independent ◽  
Rotor Surface ◽  
Independent Model

A numerical model developed by Thorat & Childs [1] has indicated that the conventional frequency independent model for labyrinth seals is invalid for rotor surface velocities reaching a significant fraction of Mach 1. A theoretical one-control-volume (1CV) model based on a leakage equation that yields a reasonably good comparison with experimental results is considered in the present analysis. The numerical model yields frequency-dependent rotordynamic coefficients for the seal. Three real centrifugal compressors are analyzed to compare stability predictions with and without frequency-dependent labyrinth seal model. Three different compressor services are selected to have a comprehensive scenario in terms of pressure and molecular weight (MW). The molecular weight is very important for Mach number calculation and consequently for the frequency dependent nature of the coefficients. A hydrogen recycle application with MW around 8, a natural gas application with MW around 18, and finally a propane application with molecular weight around 44 are selected for this comparison. Useful indications on the applicability range of frequency dependent coefficients are given.

Rotordynamic Characteristics of the Straight-Through Labyrinth Seal Based On the Applicability Analysis of Leakage Models Using Bulk-Flow Method

2021 ◽  
Author(s):  
Tianhao Wang ◽  
Zhigang Li ◽  
Jun Li
Keyword(s):  
Rotational Speed ◽  
Control Volume ◽  
Labyrinth Seal ◽  
Bulk Flow ◽  
Inlet Pressure ◽  
Leakage Flow ◽  
Flow Method ◽  
Leakage Model ◽  
Outlet Pressure ◽  
Prediction Approach

Abstract Labyrinth seals are widely applied in the turbomachinery to control the leakage flow through the clearance between the stationary and rotating components. The fluid excitation induced by the labyrinth seal would deteriorate the stability of turbomachinery shaft. Developing an accurate and rapid prediction approach is crucial for the analysis of the fluid excitation rotordynamics of the labyrinth seal. The objective of this study is to analyze the applicability of leakage models using Bulk-Flow method and investigate the factors affecting the rotordynamic characteristics of the labyrinth seal. An elliptical orbit for rotor whirling was assumed in the one-control-volume Bulk-Flow model considering an isentropic process to predict the frequency-dependent rotordynamic coefficients of the labyrinth seal. The optimal leakage model was determined by comprehensively analyzing the applicability of 72 leakage models. Employing the optimal leakage model in the Bulk-Flow method, the effects of sealing clearance, pressure ratio, preswirl ratio and rotational speed on the rotordynamic characteristics of the labyrinth seal were investigated. The conclusions show that the Bulk-Flow method has an average prediction error of around 10% for the leakage flow rate, cross-coupled stiffness and direct damping when equipped with the optimal leakage model. Increasing preswirl ratio has a significantly destabilizing effect on the rotor stability, while the influence of increasing rotational speed is strongly related to preswirl direction. The effective damping of the labyrinth seal is sensitive to the inlet pressure, but insensitive to the outlet pressure and sealing clearance. The crossover frequency is almost impervious to the inlet pressure, outlet pressure and sealing clearance.

Experimental Rotordynamic Coefficient Results for: (a) A Labyrinth Seal With and Without Shunt Injection and (b) A Honeycomb Seal

1998 ◽  
Author(s):  
Elias A. Soto A. ◽  
Dara W. Childs
Keyword(s):  
Pressure Ratio ◽  
Injection Pressure ◽  
Labyrinth Seal ◽  
Surface Velocity ◽  
Labyrinth Seals ◽  
Honeycomb Seal ◽  
Radial Injection ◽  
Rotor Surface ◽  
Rotordynamic Coefficient ◽  
Better Than

Centrifugal compressors are increasingly required to operate at higher pressures, speeds, and fluid density. In these conditions, compressors are susceptible to rotordynamic instabilities. To remedy this situation, labyrinth seals have sometimes been modified by using shunt injection. In shunt injection, the gas is taken from the diffuser or discharge volute and injected into an upstream chamber of the balance-piston labyrinth seal. The injection direction can be radial or against rotation. This study contains the first measured rotordynamic data for labyrinth seals with shunt injection. A comparison has been made between conventional labyrinth seals, labyrinth seal with shunt injection (radial and against rotation), and a honeycomb seal. Labyrinth seals with injection against rotation are better able to control rotordynamic instabilities than labyrinth seals with radial injection; however, the leakage is slightly higher. The leakage comparison for all seals demonstrates that the honeycomb seal has the best flow control. Test data are presented for a top rotor surface velocity of 110 m/sec, a supply pressure of 13.7 bars, and IPr = 0.95 (injection pressure is 1.05 = 1/0.95 times the seal inlet pressure). For these conditions, and considering effective damping, the labyrinth seal with injection against rotation is better than the honeycomb seal when the pressure ratio across the seal PR<0.45. On the other hand, the honeycomb seal is better when PR>0.45. The effectiveness of the shunt-injection against rotation in developing effective damping is reduced with increasing rotor surface velocity.

Application of Computational Fluid Dynamics Analysis for Rotating Machinery—Part II: Labyrinth Seal Analysis

2005 ◽  
Vol 127 (4) ◽  
pp. 820-826 ◽  
Author(s):  
Toshio Hirano ◽  
Zenglin Guo ◽  
R. Gordon Kirk
Keyword(s):  
Research Work ◽  
Flow Analysis ◽  
Labyrinth Seal ◽  
Bulk Flow ◽  
Working Fluid ◽  
Leakage Flow ◽  
Labyrinth Seals ◽  
Eccentric Rotor ◽  
Computational Fluid Dynamics Analysis ◽  
Force Components

Labyrinth seals are used in various kinds of turbo machines to reduce internal leakage flow. The working fluid, or the gas passing through the rotor shaft labyrinth seals, often generates driving force components that may increase the unstable vibration of the rotor. It is important to know the accurate rotordynamic force components for predicting the instability of the rotor-bearing-seal system. The major goals of this research were to calculate the rotordynamic force of a labyrinth seals utilizing a commercial CFD program and to further compare those results to an existing bulk flow computer program currently used by major US machinery manufacturers. The labyrinth seals of a steam turbine and a compressor eye seal are taken as objects of analysis. For each case, a 3D model with eccentric rotor was solved to obtain the rotordynamic force components. The leakage flow and rotor dynamics force predicted by CFX TASCFlow are compared with the results of the existing bulk flow analysis program DYNLAB. The results show that the bulk flow program gives a pessimistic prediction of the destabilizing forces for the conditions under investigation. Further research work will be required to fully understand the complex leakage flows in turbo machinery.

Rotordynamic Characterization of Labyrinth Seals in Steam Turbines: Effects of Thermal and Mechanical Loads

2018 ◽  
Author(s):  
Filippo Cangioli ◽  
Steven Chatterton ◽  
Paolo Pennacchi ◽  
Leonardo Nettis ◽  
Lorenzo Ciuchicchi ◽  
...  
Keyword(s):  
Flow Model ◽  
High Pressures ◽  
Labyrinth Seal ◽  
Bulk Flow ◽  
Critical Conditions ◽  
Accurate Estimation ◽  
Transfer Model ◽  
Steam Turbines ◽  
Labyrinth Seals ◽  
The Stability

Over the last few decades, the increasing demand on efficiency and performance for steam turbines has resulted in OEMs operating machines near critical conditions of their structural and thermal capabilities. Consequently, a more accurate estimation of the dynamic behavior of the machine has become mandatory as well as the stability assessment. Steam turbines are subjected to high temperatures, high pressures and centrifugal forces that could change the nominal geometry, especially the clearance profile in correspondence of the sealing components, occasionally generating a convergent or divergent annulus. In this paper, a new thermo-elasto bulk-flow model for labyrinth seals has been introduced. The model includes the bulk-flow model for estimating the dynamic coefficients, heat transfer model for evaluating the temperature distribution in the rotating and stationary parts and structural-mechanics model for calculating the radial growth. By considering a staggered labyrinth seal installed in the balancing drum of a steam turbine, different inlet pre-swirl ratios, as well as the stability of the seal are investigated in this paper. The model can be extremely useful for the dynamic characterisation of a wide class of labyrinth seals considering the effect of the surrounding environment on the rotordynamic coefficient prediction.

Sensitivity Analysis of the One-Control Volume Bulk-Flow Model for a 14 Teeth-on-Stator Straight-Through Labyrinth Seal

2017 ◽  
Author(s):  
Filippo Cangioli ◽  
Paolo Pennacchi ◽  
Giacomo Riboni ◽  
Giuseppe Vannini ◽  
Lorenzo Ciuchicchi ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Friction Factor ◽  
Flow Model ◽  
Control Volume ◽  
Labyrinth Seal ◽  
Operating Conditions ◽  
Bulk Flow ◽  
Mathematical Treatment ◽  
Dynamic Coefficients ◽  
The One

Since the 80s, academic research in the rotordynamics field has developed mathematical treatment for the prediction of the dynamic coefficients of sealing components. Dealing with the straight-through labyrinth seal, Iwatsubo [1], at a first stage, and Childs [2], later on, have developed the one-control volume bulk flow model. The model allows evaluating the surrounding fluid forces acting on the rotor, analyzing the fluid dynamics within the seal: the continuity, circumferential momentum and energy equations are solved for each cavity. To consider axial fluid dynamics, correlations, aiming to estimate the leakage and the pressure distribution, are required. Several correlations have been proposed in the literature for the estimation of the leakage, of the kinetic energy carry-over coefficient (KE), of the discharge coefficient and of the friction factor. After decades of research in the field of seal dynamics, the bulk-flow model has been confirmed as the most popular code in the industries, however, it is not clear which is the best set of correlations for the prediction of seal dynamic coefficients. This paper allows identifying the most accurate combination of correlations to be implemented in the bulk-flow model. The correlations are related to: the leakage formula, the flow coefficient, the KE and the friction factor. Investigating the results of several models (32 models), which consider different sets of correlations, in comparison to the experimental data (performed by General Electric Oil & Gas), it is possible to observe the dependence, of the model correlations, on the operating conditions. The experimental results, performed using a 14 teeth-on-stator labyrinth seal, investigate several operating conditions of pressure drop.

Rotordynamic Coefficients for a Tooth-on-Stator Labyrinth Seal at 70 Bar Supply Pressures: Measurements Versus Theory and Comparisons to a Hole-Pattern Stator Seal

2004 ◽  
Vol 127 (4) ◽  
pp. 843-855 ◽  
Author(s):  
Arthur Picardo ◽  
Dara W. Childs
Keyword(s):  
Control Volume ◽  
Labyrinth Seal ◽  
Test Results ◽  
Flow Models ◽  
Rotordynamic Coefficients ◽  
Volume Model ◽  
Supply Pressure ◽  
Theoretical Predictions ◽  
The One ◽  
Rotor Dynamic

Rotor dynamic and leakage coefficients are presented for a labyrinth seal that was tested at a supply pressure of 70 bar-a and speeds up to 20,200 rpm. Tests were conducted at clearances of 0.1 mm and 0.2 mm, pressure ratios of 0.10, 0.31, and 0.52, and three preswirls ratios. Comparisons are made between test data and predictions from one-control-volume and two-control-volume bulk-flow models. Generally, theoretical predictions agree poorly with the test results, with the one-control volume model giving better predictions. The one-control-volume model provides a conservative prediction for effective damping; i.e., this parameter is underestimated. Both models under predict leakage rates. Comparisons are also made between rotordynamic coefficients of labyrinth and hole-pattern seals.

Rotordynamic Coefficients for a Tooth-on-Stator Labyrinth Seal at 70 Bar Supply Pressures — Measurements Versus Theory and Comparisons to a Hole-Pattern Stator Seal

2004 ◽  
Author(s):  
Arthur Picardo ◽  
Dara W. Childs
Keyword(s):  
Test Data ◽  
Control Volume ◽  
Labyrinth Seal ◽  
Test Results ◽  
Flow Models ◽  
Rotordynamic Coefficients ◽  
Volume Model ◽  
Supply Pressure ◽  
Theoretical Predictions ◽  
The One

Rotordynamic and leakage coefficients are presented for a labyrinth seal that was tested at a supply pressure of 70 bar-a and speeds up to 20200 rpm. Tests were conducted at clearances of 0.1mm and 0.2mm, pressure ratios of 0.10, 0.31 and 0.52, and three pre-swirls ratios. Comparisons are made between test data and predictions from one-control-volume and two-control-volume bulk-flow models. Generally, theoretical predictions agree poorly with the test results, with the one-control volume model giving better predictions. The one-control-volume model provides a conservative prediction for effective damping; i.e., this parameter is underestimated. Both models under predict leakage rates. Comparisons are also made between rotordynamic coefficients of labyrinth and hole-pattern seals.

Sign in / Sign up

Export Citation Format

Share Document