Effects of Labyrinth Fin Wear on Aerodynamic Performance of Turbine Stages: Part I — Bending Damages

2019 ◽  
Author(s):  
Xin Yan ◽  
Xinbo Dai
Keyword(s):  
Labyrinth Seal ◽  
Flow Fields ◽  
Aerodynamic Performance ◽  
Leakage Flow ◽  
Original Design ◽  
Labyrinth Seals ◽  
Sealing Performance ◽  
Forward Bending ◽  
Design Case ◽  
Isentropic Efficiency

Abstract Labyrinth seals are widely applied in turbo machines because of their geometrical simplicity, convenient installation, reliable operation and excellent sealing performance. However, in realistic operation process, they usually encounter transient conditions (starting-up, shutting down, etc.) and unavoidable vibrations, which may cause wear in the labyrinth fins. After rubbing, the sealing performance of labyrinth seal will be varied in contrast to the original design. Correspondingly, the aerodynamic efficiency of the turbine stage will be affected by the variation of leakage flow in rubbing process. However, in published literature with respect to the labyrinth seal wear, most of the attention has been paid on revealing sealing performance degradation of labyrinth seal itself. Few studies have been concentrated on the influence of labyrinth seal wear on aerodynamic performance of turbine stages. In such background, the present paper utilizes the numerical methods to investigate the effects of labyrinth seal bending damages on aerodynamic performance of turbine stages. Firstly, under several assumptions, the bending geometrical model was established to describe different degrees of bending damages. Secondly, using three-dimensional RANS simulations, the effects of effective clearance variation due to bending on leakage flow and flow fields in turbine stages were investigated. The overall performance of the turbine stages with teeth-bending damages was also compared with the original design case. The influence of the forward bending and backward bending of labyrinth seals were analyzed and compared with each other. The total-total isentropic efficiency of turbine stages, leakage rates, outlet flow angles, reaction degrees and profile static pressure distributions, entropic distributions and flow fields in seals were obtained and compared to the original design case. The results indicate that the leakage rates in the worn labyrinth seal are quite relevant to the effective clearance, especially for the backward bending damages. As the effective clearances in backward bending cases are increased by 0.2–0.6mm, the isentropic efficiency of turbine stages is decreased by about 1–2%. However, for the forward bending damages, the aerodynamic performance and leakage rates in turbine stages are not sensitive to the effective clearance.

Performance evaluation of the inter-stage labyrinth seal for different tooth positions in an axial compressor

2017 ◽  
Vol 232 (6) ◽  
pp. 579-592 ◽  
Author(s):  
Xiaozhi Kong ◽  
Gaowen Liu ◽  
Yuxin Liu ◽  
Zhao Lei ◽  
Longxi Zheng
Keyword(s):  
Axial Compressor ◽  
Labyrinth Seal ◽  
Tip Clearance ◽  
Test Facility ◽  
Leakage Flow ◽  
Rotating Disc ◽  
Labyrinth Seals ◽  
Leakage Flows ◽  
Sealing Performance ◽  
Set Up

Labyrinth seals are normally used to control the leakage flow in the compressor stator well. The upstream and downstream rotor-stator cavities of the labyrinth seal can cause complex reverse leakage flows. Remarkable temperature increases and high swirl velocities are observed in this region. In addition, another characteristic of inter-stage labyrinth seal is that large expansions of rotor and stator may easily lead to severely rubbing between the teeth and shrouds, which can shorten the lifetime of the compressor obviously. Experiments were conducted at a rotating compressor inter-stage seal test facility. Different labyrinth rings were tested to compare the performances of inter-stage labyrinth seals with different tooth positions. Leakage flow rates, windage heating and swirl ratios in the outlet cavity were measured at different rotating speeds and pressure ratios. In order to get the working tip clearance accurately, the set up tip clearance was measured with plug gauges, while the radial displacements of rotating disc and stationary casing were measured separately with two high precision laser distance sensors. Numerical simulations were carried out to present the important flow physics responsible for the effects of different tooth positions. In this article, performances of different cases for single, double and triple teeth were investigated and the experimental data provide a new way for the design of inter-stage seals. This method can reduce the leakage flow and avoid severely rubbing at the same time by changing axial positions of teeth in the stator well. When teeth are placed downstream of the model and the tooth pitch is larger, the inter-stage seal would have better sealing performance. For triple teeth cases, N = 3-Case1 has the lowest discharge coefficients, 15% less than that of N = 3-Baseline.

scholarly journals Effects of Double-Side Labyrinth Seals on Aerodynamic Performance in a Transonic Shrouded Turbine Stage

2020 ◽  
Vol 142 (2) ◽  
Author(s):  
Weihang Li ◽  
Shaowen Chen ◽  
Hongyan Liu ◽  
Zhihua Zhou ◽  
Songtao Wang
Keyword(s):  
Labyrinth Seal ◽  
Aerodynamic Performance ◽  
Maximum Efficiency ◽  
Outlet Section ◽  
Leakage Flow ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Labyrinth Seals ◽  
Tip Leakage ◽  
Transonic Turbine

Abstract Labyrinth seals on both rotor casing and blade tip as an effective method to control the leakage flowrate of the shroud and improve aerodynamic performances in a transonic turbine stage are investigated in this study. Compared to the case without the labyrinth seal structure, the cases with three different types of sealing teeth have been shown to reduce significantly the tip leakage flow by computational simulations. The double-side sealing teeth case reduces the leakage flowrate mleakage/mpassage from 3.4% to 1.3% and increases the efficiency by 1.4%, which is the maximum efficiency improvement of all cases. The sealing structures increase the loss inside the shroud while reducing the momentum mixing between shroud leakage flow and mainstream. Therefore, the circumferential distribution of leakage velocity is changed, as well as the distribution of high-loss zones at turbine outlet. Furthermore, the leakage-vortex loss, which is associated with the blockage effect of sealing structure to the tip leakage flow, gains more improvement than the passage-vortex at the rotor outlet section in double-side seal case. In addition, it has also been found that with a larger gap at tip, the double-side seal has better effects of reducing the leakage flow and improving the aerodynamic performance in the transonic turbine stage.

Effects of Pressure Ratio and Fin Pitch on Leakage Flow Characteristics in High Rotating Labyrinth Seals

2006 ◽  
Author(s):  
Jun Li ◽  
Xin Yan ◽  
Zhenping Feng
Keyword(s):  
Flow Rate ◽  
Geometrical Structure ◽  
Pressure Ratio ◽  
Flow Characteristics ◽  
Labyrinth Seal ◽  
Leakage Flow ◽  
Rotational Axis ◽  
Labyrinth Seals ◽  
Sealing Performance ◽  
Leakage Flow Rate

Labyrinth seals represent an important flow element in the sealing equipment of modern turbomachinery industries. The straight-through and stepped labyrinth seal are widely used in modern steam turbine due to their comparable simple structure and low manufactured costs. The influence of pressure ratio and fin pitch on the leakage flow characteristics of the straight-through and stepped labyrinth seals is numerically determined. The pressure ratio is defined as the outlet static pressure divided by the inlet total pressure. The fin pitch varied in the fixed axial distance of the labyrinth seal. The geometries investigated represent designs of the straight-through and stepped labyrinth seal typical for modern steam turbines. The leakage flow fields in the high rotating straight-through and stepped labyrinth seals are obtained by the Reynolds-Averaged Navier-Stokes solution using the commercial software FLUENT with the fixed seal clearance and fins geometrical structure. The effect of the rotational axis is also taken into account in numerical computations. Numerical simulations covered a range of pressure ratio and fin pitch for the straight-through and stepped labyrinth seals. Dimensionless discharge coefficients, describing the sealing performance, are calculated from the simulation results. The numerical results show that pressure ratio and fin pitch both affects the sealing performance with the fixed seal clearance and fin geometrical structure. The leakage flow rate decreases with the decreasing fin pitch for both the straight-through and stepped labyrinth seal at the fixed pressure ratio. Furthermore, the leakage flow rate decreases with the increasing pressure ratio at the fixed fin pitch for two kinds of labyrinth seals in the present study. This research provides technical support for improved design of labyrinth seals in turbomachinery.

Leakage flow analysis in the gas turbine shroud gap

2019 ◽  
Vol 91 (8) ◽  
pp. 1077-1085 ◽  
Author(s):  
Filip Wasilczuk ◽  
Pawel Flaszynski ◽  
Piotr Kaczynski ◽  
Ryszard Szwaba ◽  
Piotr Doerffer ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Gas Turbine ◽  
Mass Flow ◽  
Labyrinth Seal ◽  
Leakage Flow ◽  
Original Design ◽  
Reference Case ◽  
Content Type ◽  
Flow Through ◽  
The Impact

Purpose The purpose of the study is to measure the mass flow in the flow through the labyrinth seal of the gas turbine and compare it to the results of numerical simulation. Moreover the capability of two turbulence models to reflect the phenomenon will be assessed. The studied case will later be used as a reference case for the new, original design of flow control method to limit the leakage flow through the labyrinth seal. Design/methodology/approach Experimental measurements were conducted, measuring the mass flow and the pressure in the model of the labyrinth seal. It was compared to the results of numerical simulation performed in ANSYS/Fluent commercial code for the same geometry. Findings The precise machining of parts was identified as crucial for obtaining correct results in the experiment. The model characteristics were documented, allowing for its future use as the reference case for testing the new labyrinth seal geometry. Experimentally validated numerical model of the flow in the labyrinth seal was developed. Research limitations/implications The research studies the basic case, future research on the case with a new labyrinth seal geometry is planned. Research is conducted on simplified case without rotation and the impact of the turbine main channel. Practical implications Importance of machining accuracy up to 0.01 mm was found to be important for measuring leakage in small gaps and decision making on the optimal configuration selection. Originality/value The research is an important step in the development of original modification of the labyrinth seal, resulting in leakage reduction, by serving as a reference case.

A CFD Study on the Dynamic Coefficients of Labyrinth Seals

2012 ◽  
Author(s):  
Donghui Zhang ◽  
Chester Lee ◽  
Michael Cave
Keyword(s):  
High Speed ◽  
Fluid Dynamic ◽  
Labyrinth Seal ◽  
Leakage Flow ◽  
Labyrinth Seals ◽  
Dynamic Coefficients ◽  
Rotating Impeller ◽  
Coupling Stiffness ◽  
Direct Stiffness ◽  
Compressor Efficiency

Labyrinth seals are widely used in gas compressors to reduce internal leakage and increase the compressor efficiency. Due to the eccentricity between the rotating impeller and the stationary part as *well as the shaft whirling motion, forces are generated when the leakage flow passing through the cavities and the seals. For a lot of applications with high speed and pressure, these forces can drive the system unstable. Thus, predicting the forces accurately become a very important for compressor rotordynamic designs. A lot of research and studies has been done to the seals itself, including bulk flow method, computational fluid dynamic (CFD) and test measurement. The seal and leakage flow interaction forces can be predicted relatively accurate. But very few research treat the seal and cavities as one component interacting with the leakage flow and produce the forces. This paper presents results of CFD investigations on the dynamic coefficients of one typical impeller eye seal and front cavity. The CFD results show that large forces are generated in the front cavity due to circumferential uniform pressure distribution, which caused by the downstream labyrinth seal. The forces generated in the front cavity are more than in the front seal. It was found that the inertia, damping, and stiffness are proportional to average pressure. The cross-coupling stiffness increases with speed with power of 2 while the direct stiffness increases with speed with power of about 1.7.

Numerical Comparison of Leakage Flow and Rotordynamic Characteristics for Two Types of Labyrinth Seals With Baffles

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
Yuanqiao Zhang ◽  
Jun Li ◽  
Zhigang Li ◽  
Xin Yan
Keyword(s):  
Rotational Speed ◽  
Flow Resistance ◽  
Labyrinth Seal ◽  
Leakage Flow ◽  
Numerical Comparison ◽  
Vibration Frequencies ◽  
Labyrinth Seals ◽  
Rotordynamic Coefficients ◽  
Brush Seal ◽  
Swirl Intensity

Abstract Cavity separation baffles can decrease the circumferential swirl intensity of labyrinth seals and increase the seals' rotordynamic characteristics. Compared with conventional baffles, the bristle packs of brush seal baffles can contact the rotor directly, thereby further reducing the swirl intensity of the seal cavity. This paper, using the numerical model combining a multifrequency elliptical whirling orbit model, a porous medium model, and transient Reynolds-averaged Navier–Stokes (RANS) solutions, compares the leakage flow and rotordynamic characteristics of a labyrinth seal with brush-seal baffles (LSBSB) and a labyrinth seal with conventional baffles (LSCB). Ideal air flows into the seal at an inlet preswirl velocity of 0 m/s (or 60 m/s or 100 m/s), total pressure of 690 kPa, and temperature of 14 °C. The outlet static pressure is 100 kPa and the rotational speed is 7500 r/min (surface speed of 66.8 m/s) or 15,000 r/min (surface speed of 133.5 m/s). Numerical results show that the LSBSB possesses the slightly less leakage flow rate than the LSCB due to the flow resistance of the bristle pack to the fluid. Compared with the LSCB, the LSBSB shows a higher positive effective stiffness (Keff) at all considered vibration frequencies and a higher effective damping (Ceff) for most vibration frequencies. What is more, the crossover frequency (fc0) of the LSBSB is significantly lower than that of the LSCB, which means that the LSBSB has a wider frequency range offering positive effective damping. The increasing inlet preswirl velocity and rotational speed only slightly affect the Keff for both seals. The Ceff of two seals decreases as the inlet preswirl velocity rises, especially for the LSCB. The Ceff of the LSCB slightly decreases because of the increasing rotational speed. In contrast, the Ceff of the LSBSB is not sensitive to the changes in rotational speed. In a word, the LSBSB possesses superior rotordynamic performance to the LSCB. Note that this work also investigates the leakage flow and rotordynamic characteristics a labyrinth seal with inclined baffles (LSIB) under the condition of u0 = 60 m/s and n = 15,000 r/min. The inclined baffles of the LSIB are same as the backing plates of LSBSB baffles. The LSIB has rotordynamic coefficients almost equal to the LSCB. Hence, the reason why the LSBSB possesses better rotordynamic performance than that of the LSCB is the flow resistance of bristle packs of brush seal baffles, not the inclination direction variation of baffles.

Numerical Investigations of Leakage Performance Degradations in Labyrinth and Flexible Seals Due to Wear

2020 ◽  
Author(s):  
Xinbo Dai ◽  
Xin Yan ◽  
Kun He ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Labyrinth Seal ◽  
Leakage Rate ◽  
Labyrinth Seals ◽  
Element Analysis ◽  
Numerical Investigations ◽  
Forward Bending ◽  
The Finite Element Analysis ◽  
Before And After ◽  
Computational Fluid Dynamics Cfd ◽  
Wear Damage

Abstract The Finite Element Analysis (FEA) and Computational Fluid Dynamics (CFD) methods are utilized to investigate the leakage performance degradations in two kinds of flexible seals (i.e. forward bending and backward bending) and two kinds of shroud labyrinth seals (i.e. with straight fins and chamfered fins) in rubbing events. With the existing experimental data, FEA methods for contacting simulations and CFD methods for leakage rate and flow pattern predictions are carefully examined. The wear characteristic and leakage performance between labyrinth seals and flexible seals are compared before and after rub. The results show that, in rubbing process, the labyrinth seal with straight (symmetrical) fins is likely to undergo the mushrooming damage, whereas the labyrinth seal with chamfered (asymmetrical) fins is likely to undergo the tooth-bending damage. In rubbing process, compared with the labyrinth seal, the flexible seal has a superior characteristic in resisting the wear damage due to increased flexibility of fin. For a labyrinth seal with 0.3mm design clearance and a flexible seal with 0.15mm design clearance, the 0.5mm radial displacement of rotor will result in 110% increase of leakage rate for labyrinth seal, and 7% increase of leakage rate for flexible seal after wear. Under the same conditions, the forward bending flexible seal has a lower leakage rate than the backward bending flexible seal before and after rub.

Effects of Labyrinth Fin Wear on Aerodynamic Performance of Turbine Stages: Part II — Mushrooming Damages

2019 ◽  
Author(s):  
Xinbo Dai ◽  
Xin Yan
Keyword(s):  
Experimental Studies ◽  
Axial Direction ◽  
Labyrinth Seal ◽  
Aerodynamic Performance ◽  
Leakage Rate ◽  
Secondary Flows ◽  
Main Function ◽  
Aerodynamic Loss ◽  
Solution Methods ◽  
Isentropic Efficiency

Abstract The main function of labyrinth seal is to control leakage flow in clearance that involves with rotating and stationary parts. Therefore, the effective of clearance gap in labyrinth seal is critical to sealing, heat transfer and vibration characteristics. However, due to the mechanical expansions, vibrations, thermal stress, misalignment of seal components in transient periods of startup, shutdown and hot restart, the stationary and rotating parts of the labyrinth seal are likely to contact each other, causing wear damages in labyrinth fin. Mushrooming damages are often occurred in the rubbing events when labyrinth fin is made of soft material compared with the opposite component. To investigate how mushrooming damage affects the leakage performance of labyrinth seal, many numerical and experimental studies have been carried out in last decades. However, little attention has been paid on the influence of labyrinth fin mushrooming on aerodynamic performance of turbine stages. In this study, using the RANS equations solution methods, the effect of labyrinth fin mushrooming on isentropic efficiency, leakage rates, outlet flow angles, reaction degrees, profile static pressure distributions and flow fields in turbine stages were investigated at three different mushrooming radii and three effective clearances. It shows the leakage rate is increased with increasing the mushroom radius and effective clearance. At the same effective clearance, as the mushrooming radius increases from 0.2mm to 0.4mm, the leakage rate is increased by about 0.19–0.32%, and the overall isentropic efficiency is decreased by 0.78%. At the same mushrooming radius, as the effective clearance increases from 1mm to 1.4mm, the leakage rate is increased by 0.21–0.31%, and the overall isentropic efficiency is decreased by 0.65%. As mushroom radius and effective clearance increase, the secondary flows near hub and shroud are intensified and developed along axial direction, causing pronounced aerodynamic loss in turbine stages.

Development of a New Loss Model for Turbomachinery Labyrinth Seals

2021 ◽  
Author(s):  
Davendu Y. Kulkarni ◽  
Luca di Mare
Keyword(s):  
Flow Rate ◽  
Labyrinth Seal ◽  
Leakage Flow ◽  
Labyrinth Seals ◽  
Stream Tube ◽  
Flow Area ◽  
Loss Model ◽  
Seal Design ◽  
Wide Range ◽  
Numerical Experimentation

Abstract The preliminary design of labyrinth seals requires a fast and accurate estimate of the leakage flow. While the conventional bulk flow models can quickly predict labyrinth seal discharge characteristics, they lack the accuracy and pragmatism of modern CFD technique and vice-a-versa. This paper presents a new 1D loss model for straight-through gas labyrinth seals that can provide quick seal leakage flow predictions with CFD-equivalent accuracy. The present seal loss model is developed using numerical experimentation technique. Multiple CFD computations are conducted on straight-through labyrinth seal geometries for a range of pressure ratios. A distinct post-processing methodology is developed to extract the through-flow stream tube in seal. Total pressure losses and flow area variations experienced by the flow in seal stream-tube are systematically accounted for based on the well-known knife-to-knife (K2K) methodology. Regression analyses are conducted on the trends of variations of loss and area coefficients to derive the independent pressure loss and flow area correlations. These novel correlations can predict the bulk leakage flow rate, windage flow rate and inter-knife static pressures over a wide range of variation of flow and geometry parameters. Validation study shows that the leakage mass flow rate predicted by this model is accurate within ±8% of measured test data. This fast and accurate model can be employed for various applications such as, in seal design-analysis workflows, for secondary air system (SAS) performance analysis and for the rotor-dynamic and aeroelastic assessments of seals.

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.

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