Seal Leakage Research Articles

Leakage and Rotordynamic Force Coefficients of A Three-Wave (Air in Oil) Wet Annular Seal: Measurements and Predictions

In subsea environments, multiphase pumps and compressors add pressure to the process fluid, thus enabling long distance tie back systems that eliminate topside oil and gas separation stations. One challenge to construct a reliable multiphase pump or a reliable wet gas compressor is that the first must handle, without process upset, a mixture whose gas volume fraction (GVF) changes suddenly; while the other must remain stable while working with a liquid volume fraction (LVF) changing over long periods of time. The mixture GVF/LVF affects the static and dynamic forced performance of secondary flow components, namely seals, and which could lead to an increase in both rotor lateral or axial vibrations, thus compromising system reliability and availability. The current research is a planned endeavor toward developing seal configurations amenable to maintain rotor dynamic characteristics during changes in the contents of flow components. This paper extends prior work with uniform clearance annular seals and presents the static and dynamic forced performance of a three-wave surface annular seal designed to deliver a significant centering stiffness. The test element has length L = 43.4 mm, diameter D = 127 mm, and mean radial clearance cm=0.191 mm. At a shaft speed of 3.5 krpm (23 m/s surface speed), an air in ISO VG 10 oil mixture with an inlet GVF, 0 to 0.9, feeds the seal at 2.5 bara pressure and 37 °C temperature. The mixture mass flow rate decreases continuously with an increase in inlet GVF; shaft speed has little effect on it. Dynamic load tests serve to identify the seal dynamic force coefficients. The liquid seal (GVF = 0) shows frequency independent force coefficients. However, operation with a mixture produces stiffnesses that vary greatly with excitation frequency, in particular the direct one that hardens. The direct damping coefficients are not functions of frequency albeit dropping rapidly in magnitude as the GVF increases. The work also compares the performance of the wavy seal against those of two other seals: one with clearance equal to the mean clearance of the wavy seal, and the other with a large clearance emulating a fully worn wavy seal. The small clearance seal leaks 20% less than the wavy seal, whereas the leakage of the worn seal is twofold that of the wavy seal. For the three seals, the leakage normalized with respect to a pure liquid condition collapses into a single curve. The wavy seal produces the greatest direct stiffness and damping coefficients, whereas the worn seal produces the smallest force coefficients. Derived from a homogeneous mixture bulk flow model, predicted force coefficients for the three-wave seal match well with the test data for operation with a pure oil and an inlet GVF 0.2. For operation with GVF > 0.2, the discrepancy between the prediction and experimental data grows rapidly. The extensive test campaign reveals a wavy-surface seal offers a centering stiffness ability, a much desired feature in vertical submersible pumps that suffer from persistent static and dynamic stability issues.

Numerical Investigation on the Leakage and Rotordynamic Characteristics for Three Types of Annular Gas Seals in Wet Gas Conditions

The modern compressor operation is challenged by the liquid presence in wet gas operating conditions. The liquid phase may affect the compressor stability by partially flooding the internal annular gas seals and inducing subsynchronous vibration (SSV). To improve the annular seal behavior and increase the rotor stability, high-precision results of leakage flow rates and rotordynamic force coefficients are needed for annular gas seals in wet gas conditions. In order to better understand the leakage and rotordynamic characteristics of the annular gas seal in wet gas conditions, a 3D transient CFD-based perturbation method was proposed for computations of leakage flow rates and rotordynamic force coefficients of annular gas seals with liquid phase in main gas phase, based on inhomogeneous Eulerian-Eulerian multiphase flow model, mesh deformation technique, and the multifrequency rotor whirling orbit model. Numerical results of frequency-dependent rotordynamic force coefficients and leakage flow rates were presented and compared for three types of noncontact annular gas seals, which include a smooth plain annular seal (SPAS), a labyrinth (LABY) seal, and a fully partitioned pocket damper seal (FPDS). These three seals were designed to have the identical rotor diameter, sealing clearance, and axial length. The accuracy and the availability of the present transient CFD numerical method were demonstrated with the experiment data of leakage flow rates and frequency-dependent rotordynamic force coefficients of the smooth plain seal with four inlet liquid volume fractions (LVFs) of 0%, 2%, 5%, and 8%. Steady and transient numerical simulations were conducted at inlet air pressure of 62.1 bar, pressure ratio of 0.5, rotational speed of 15,000 rpm, and inlet preswirl ratio of 0.3 for four inlet LVFs varying from 0% to 8% and 14 subsynchronous and synchronous whirling frequencies up to 280 Hz. The numerical results show that the inlet liquid phase has a significant influence on the leakage and rotordynamic coefficients for all three types of annular gas seals. The mixture leakage flow rate increases with the increasing inlet LVF, combining the decreasing gas-phase and linearly increasing liquid-phase leakage flow rates. The smooth plain seal leaks the most gas phase and liquid phase, followed by the pocket damper seal (PDS) and then the labyrinth seal. Increasing inlet LVF significantly decreases the direct stiffness and slightly increases the effective damping of the smooth plain seal. The labyrinth seal possesses evident negative direct stiffness and shows a noticeable decreasing effective damping with the increasing inlet LVF at the subsynchronous frequency range. Increasing inlet LVF obviously increases all the force coefficients of the pocket damper seal including the positive effective damping. From a rotordynamic viewpoint, the FPDS possesses a better liquid tolerant capability and so is a better sealing scheme for the balance piston seals and center seals of the centrifugal compressor in wet gas operating condition.

Using mercury injection pressure analyses to estimate sealing capacity of the Tuscaloosa marine shale in Mississippi, USA: Implications for carbon dioxide sequestration

This work used mercury injection capillary pressure (MICP) analyses of the Tuscaloosa Group in Mississippi, including the Tuscaloosa marine shale (TMS), to assess their efficacy and sealing capacity for geologic carbon dioxide (CO2) sequestration. Tuscaloosa Group porosity and permeability from MICP were evaluated to calculate CO2 column height retention. TMS and Lower Tuscaloosa shale samples have, respectively, Swanson permeability values less than 0.003 md and 0.00245 md; porosity from 3.86% to 9.86% and 1.34% to 7.96%; median pore throat sizes from 0.00342 to 0.0111 μm and 0.00311 to 0.017 μm; and pore radii from 0.0130 to 0.152 μm and 0.0132 to 0.149 μm. Mercury entry pressures for the TMS and Lower Tuscaloosa range from 4.9 to 57.1 MPa and 5.0 to 56.3 MPa, respectively. Calculated CO2 column heights that the TMS sample set can retain in the reservoir range from 23 to 255 m when the TMS is near 100% water saturation. Potential top seal leakage is more likely to be influenced by the numerous well penetrations through the confining system of the TMS rather than capillary failure. Results of this study demonstrate desirable sealing capacity of the TMS for geologic CO2 sequestration in reservoir sandstones of the Lower Tuscaloosa and could provide an analogue to other potential CO2 sequestration top seals.

On the Leakage, Torque, and Dynamic Force Coefficients of Air in Oil (Wet) Annular Seal: A Computational Fluid Dynamics Analysis Anchored to Test Data

Subsea pumps and compressors must withstand multiphase flows whose gas volume fraction (GVF) or liquid volume fraction (LVF) varies over a wide range. Gas or liquid content as a dispersed phase in the primary stream affects the leakage, drag torque, and dynamic forced performance of secondary flow components, namely seals, thus affecting the process efficiency and mechanical reliability of pumping/compressing systems, in particular during transient events with sudden changes in gas (or liquid) content. This paper, complementing a parallel experimental program, presents a computational fluid dynamics (CFD) analysis to predict the leakage, drag power, and dynamic force coefficients of a smooth surface, uniform clearance annular seal supplied with air in oil mixture whose inlet GVF varies discretely from 0.0 to 0.9, i.e., from a pure liquid stream to a nearly all-gas content mixture. The test seal has uniform radial clearance Cr = 0.203 mm, diameter D = 127 mm, and length L = 0.36 D. The tests were conducted with an inlet pressure/exit pressure ratio equal to 2.5 and a rotor surface speed of 23.3 m/s (3.5 krpm), similar to conditions in a pump neck wear ring seal. The CFD two-phase flow model, first to be anchored to test data, uses an Euler–Euler formulation and delivers information on the precise evolution of the GVF and the gas and liquid streams' velocity fields. Recreating the test data, the CFD seal mass leakage and drag power decrease steadily as the GVF increases. A multiple-frequency shaft whirl orbit method aids in the calculation of seal reaction force components, and from which dynamic force coefficients, frequency-dependent, follow. For operation with a pure liquid, the CFD results and test data produce a constant cross-coupled stiffness, damping, and added mass coefficients, while also verifying predictive formulas typical of a laminar flow. The injection of air in the oil stream, small or large in gas volume, immediately produces force coefficients that are frequency-dependent; in particular the direct dynamic stiffness which hardens with excitation frequency. The effect is most remarkable for small GVFs, as low as 0.2. The seal test direct damping and cross-coupled dynamic stiffness continuously drop with an increase in GVF. CFD predictions, along with results from a bulk-flow model (BFM), reproduce the test force coefficients with great fidelity. Incidentally, early engineering practice points out to air injection as a remedy to cure persistent (self-excited) vibration problems in vertical pumps, submersible and large size hydraulic. Presently, the model predictions, supported by the test data, demonstrate that even a small content of gas in the liquid stream significantly raises the seal direct stiffness, thus displacing the system critical speed away to safety. The sound speed of a gas in liquid mixture is a small fraction of those speeds for either the pure oil or the gas, hence amplifying the fluid compressibility that produces the stiffness hardening. The CFD model and a dedicated test rig, predictions and test data complementing each other, enable engineered seals for extreme applications.

A systematic study of the impact of changes of roller compactor equipment on granule and tablet properties

Typical industrial development of roller compaction processes include changes in scale from laboratory to pilot and then further to production scale and also changes in equipment design due to equipment availability in different manufacturing facilities. Transfer and scale-up of roller compaction processes based on conservation of ribbon density is relatively well established, although different equipment designs, such as side seals and ribbon milling systems can lead to changes in downstream quality attributes, including granules and tablets. The aim of this study was to investigate this transfer/scale-up approach by systematically comparing the ribbon, granule and tablet properties between three different roller compactors from the vendors: Hosokawa, Alexanderwerk and Gerteis. A larger amount of uncompacted material was observed for the Hosokawa compared to Alexanderwerk and Gerteis, partly due to side seal leakage. To reduce the material bypass fraction, the Hosokawa was modified by using tight polymer cheek plates and concave rolls although the granules still exhibited a large amount of fines. One cause is the key difference in the roll force control. The roll force on the Hosokawa is controlled by proportional–integral–derivative (PID) regulation of the feeders, which leads to large force variations. In contrast, the Alexanderwerk and Gerteis achieve an almost constant force by using a hydraulic pressure system. Granules from all roller compactors were successfully pressed into tablets, and there was no correlation between the particle size and tabletability. However, the tabletability was better for granules from ribbons with higher porosity, which indicated an effect of granule hardening in the roller compaction step. This work demonstrates that conserving ribbon porosity when moving between different roller compactors is not sufficient to achieve granules with identical properties, indicating that a more advanced approach is needed for scale-up or transfer.

Influence of Exit-Recovery Coefficient on the Leakage and Dynamic Characteristics of Annular Seal

In order to study the effect of exit-recovery coefficient on leakage performance and dynamic characteristics of finite-length annular seal, a new boundary condition including exit-recovery coefficient is applied to the solution of the first-order perturbation equations according to bulk-flow model and small disturbance hypothesis. The theoretical results are validated by the experimental results with the minimum and maximum error percentage being 0.22% and 4.33%, respectively. On the basis of the accurate model, the influences of exit-recovery coefficient on leakage performance, dynamic coefficients and stability are investigated in detail. The calculated results imply that the exit-recovery coefficient needs to be considered in the characteristic research of annular seal. The exit-recovery coefficient is proportional to principle stiffness, while it is inversely proportional to leakage, principle damping, cross-coupled stiffness and damping. In addition, the exit-recovery coefficient has little effect on the stability of annular seal. The theoretical model including the exit-recovery coefficient is closer to actual condition and the results can provide references for the design of annular seal and multistage pump rotor system.

Experimental Study on Performances of Carbon Seal and Finger Seal under High-speed and High-pressure Condition

Carbon seal and finger seal are both advanced and used in aero-engine and gas turbine. Compared with the finger seal, the application of carbon seal is longer and its technology is more mature. But the finger seal also has excellent sealing performance, and it is much more economical than carbon seal. Based on a self-developed dynamic sealing test rig, the experimental studies on performances of carbon seal and finger seal under high-speed and high-pressure conditions are carried out in this paper, and the comparison on leakage and durability of the two seals is carried out in-depth to find the possibility that replacing carbon seal with finger seal, which can provide references for the selection of sealing types. The experimental results show that, under the same structural and operating conditions, the durability of carbon seal is better than that of the metal matrix finger seal, but the leakage of finger seal is smaller. Considering the manufacturing costs, the finger seal has potential to replace carbon seal at lower speed. Therefore, developing nonmetallic finger seal is an effective way to promote advanced sealing technology, which combines the flexible structure of finger seal with new material that has high thermal conductivity, low expansion, and low friction.

Experimental and Numerical Investigations of Closed Radial Inflow Turbine With Labyrinth Seals

It is a common practice to use closed impeller in radial inflow turbine against the flow leakage from tip clearance of impellers, especially in small volume flow condition. It utilizes labyrinths between the shroud and the case to abate the higher pressure leakage. Experimental and computational investigations of shroud clearance flow in a radial inflow turbine with labyrinth seals are presented in this paper. Compared with the result without leakage, numerical computation result including the leakage of labyrinth seals agrees better with that of the experiment result, which indicates that the leakage of labyrinth seals cannot be neglected. Several geometrical arrangements with a series of different clearance of labyrinth seals are investigated experimentally and numerically, and the dimensionless shroud clearance is of 0%, 0.6%, 1.2%, 1.8%, 2.7%, 3.6%. Finally, the character of flow and loss is analyzed by computational fluid dynamics (CFD) tools. The results indicate that the labyrinth seal flow has no effect on the main flow passage and mainly causes different leakage mass flow.

Leakage and wear characteristics of finger seal in hot/cold state for aero-engine

Experimental investigation has been done to approach the leakage and wear characteristics of finger seal in hot/cold state. The High-speed Sealing Test Rig was used in the study. Leakage measurements were done in terms of different working parameters. The pressure ratio changed from 1.1 to 1.8 and the rotating speed varied from 0 to 5000 rpm. The temperature altered from 283 K to 433 K to achieve the cold state and hot state, respectively. Two groups of durability tests were carried out in hot/cold state, separately. Each durability test lasted 300 h with two finger seals. An accurate optical measuring instrument was applied to record the wear growth of the finger seals. Results showed that the flow factor monotonously increases with the pressure ratio and decreases with the rotating speed. An attractive feature is firstly captured that the finger seal with double-laminate achieves lower leakage in cold state while the finger seal with triple-laminate behaves better in hot state. Full life-cycle theory was applied to analyse the wear of the finger seal. The wear growth curve exhibits a rule of SPSP (Sharp Wear, Progressive Wear, Stable Wear and Permanent Wear). Of particular interest is the wear comparison between hot state and cold state, which is firstly discussed in the study and shows that finger seals operating in hot state generate obviously more wear than those in cold state.

Leakage and Stiffness Characteristics of Bionic Cluster Spiral Groove Dry Gas Seal

Spiral groove dry gas seal (S-DGS), the most widely used DGS in the world, encounters the problem of high leakage rate and inferior film stability when used in high-speed machinery equipment, which could not be well solved by optimization of geometrical parameters and molded line of spiral groove. A new type of bionic cluster spiral groove DGS (CS-DGS) is proved to have superior film stability than S-DGS at the condition of high-speed and low-pressure numerically. A bionic CS-DGS is experimentally investigated and compared with common S-DGS in order to provide evidence for theoretical study. The film thickness and leakage rate of both bionic spiral groove and common spiral groove DGS are measured and compared with each other and with theoretical values under different closing force at the condition of static pressure, high-speed and low-pressure, and the film stiffness and stiffness-leakage ratio of these two face seals are derived by the relationship between closing force and film thickness at the steady state. Experimental results agree well with the theory that the leakage and stiffness of bionic CS-DGS are superior to that of common S-DGS under the condition of high-speed and low-pressure, with the decreasing amplitude of 20% to 40% and the growth amplitude of 20%, respectively. The opening performance and stiffness characteristics of bionic CS-DGS are inferior to that of common S-DGS when rotation speed equals to 0 r/min. The proposed research provides a new method to measure the axis film stiffness of DGS, and validates the superior performance of bionic CS-DGS at the condition of high-speed and low-pressure experimentally.

An approach to combine the second-order and third-order analysis methods for optimization of a Stirling engine

Second-order and third-order models are the two main methods for Stirling cycle analysis. A second-order one has relatively reliable accuracy without detailed cyclic information, while a third-order one provides relatively comprehensive operational information with uncertainty. In this work, a third-order model, Sage, is tried to be improved by a second-order model, Improved Simple Analytical Model, and 100 W β-type Stirling engine is used as a modelling prototype engine. As suggested by Improved Simple Analytical Model, the gap of the piston seal and the empirical multiplier for heat transfer of cooler in Sage should be adjusted. This is accomplished by combining these two models so that the effects of seal leakage loss, gas spring hysteresis loss, and piston friction loss could be considered in an improved Sage. The improved Sage indicates that the overall relative errors for the indicated power output and the thermal efficiency are reduced by over 30 percentage points and 20 percentage points, respectively. Pressure–volume diagrams provided by the improved Sage are much closer to the experimental ones, and the pattern similarities of pressure–volume diagrams increase from 78.6–81.4% to 80.8–85.0%. Performance simulation of the Stirling engine is carried out by the improved Sage and the results show that regenerator takes a major role in improving the performance of the 100 W β-type Stirling engine. Lengths of regenerator, heater and cooler are optimized for the maximum indicated power output and the maximum thermal efficiency respectively, and the optimized values are increased by 15.9% and 25.2%, respectively.

Elliptical Shape Hole-Pattern Seals Performance Evaluation Using Design of Experiments Technique1

Hole-pattern annular gas seals have two distinct flow regions: an annular jet-flow region between the rotor and stator, and cylindrical indentions in the stator that serve as cavities where flow recirculation occurs. As the working fluid enters the cavities and recirculates, its kinetic energy is reduced, resulting in a reduction of leakage flow rate through the seal. The geometry of the cylindrical cavities has a significant effect on the overall performance of the seal. In this study, the effects of elliptical shape hole pattern geometry on the leakage and dynamic response performance of an industry-relevant hole-pattern seal design are investigated using a combination of computational fluid dynamics (CFD), hybrid bulk flow-CFD analysis, and design of experiments (DOEs) technique. The design space was defined by varying the values of five geometrical characteristics: the major and minor radius of hole, the angle between the major axis and the axis of the seal, the spacing between holes along the seal axis, and hole spacing in the circumferential direction. This detailed analysis allowed for a greater understanding of the interaction effects from varying all of these design parameters together as opposed to studying them one variable at a time. Response maps generated from the calculated results demonstrate the effects of each design parameter on seal leakage as well as the co-dependence between the design parameters. The data from this analysis were also used to generate linear regression models that demonstrate how these parameters affect the leakage rate and the dynamic coefficients, including the effective damping.

The Tribological and Sealing Properties of PFA Composites

The polytetrafluoroethylene (PTFE) and perfluoroalkoxyperfluoropropyl vinyl ether (PFA) composites were prepared using carbon fiber (CF) and glass fiber (GF) as fillers. The effects of these fillers on the tribological and sealing properties were investigated. The tribological and sealing properties of the composites were evaluated by a wear tester and a seal test rig. Results showed that the incorporation of CF and GF both improved the wear resistance with composites, approaching wear rates as low as 10−6 mm3/N·m and lowered the seal’s leakage of the PTFE/PFA composites. As described here, CF was more effective than GF in improving the wear rate. Notably, the wear rate of the PFA/CF composite is much less than that of the PTFE composites as the transfer film on the couple ring is much more unique, thick, smooth, and compact. The leakage of carbon fiber-filled PFA composite seal was lowered to 66% less than the traditional PTFE composite seals, which indicates better sealing properties.

LEAKAGE ACCOUNT FOR RADIAL FACE CONTACT SEAL IN AIRCRAFT ENGINE SUPPORT

The article is dedicated to the development of a methodology for the radial face contact seal design taking into consideration the supporting elements deformations in different aircraft engine operating modes. Radial face contact seals are popular in the aircraft engines bearing support. However, there are no published leakage calculation methodologies of these seals. Radial face contact seal leakage is determined by the gap clearance in the carbon seal ring split. In turn, the size gap clearance depends on the deformation of the seal assembly parts and from the engine operation. The article shows the leakage detection sequence in the intershaft radial face contact seal of the compressor support for take-off and cruising modes. Evaluated calculated leakage values (2.4 g/s at takeoff and 0.75 g/s at cruising) go with experience in designing seals.

A pre-test analysis of ATLAS SBO with RCP seal leakage using MARS code

The accident in Fukushima Daiichi nuclear power plants shows the important of developing coping strategies for extended station blackout (SBO) scenarios of the nuclear power plants (NPPs). Many NPPs in United State of America are applying FLEX approach as main coping strategies for extended station blackout (SBO) scenarios. In FLEX strategies, outside water injection to reactor cooling system (RCS) and steam generators (SGs) is considered as an effective method to remove residual heat and maintain the inventory of the systems during the accident. This study presents a pretest calculation using MARS code for the Advanced Thermal-hydraulic Test Loop for Accident Simulation (ATLAS) SBO experiment with RCP seal leakage scenario. In the calculation, the turbinedriven auxiliary feed water pumps (TDAFPs) are firstly used after SBO initiation. Then, the outside cooling water injection method is used for long term cooling. In order to minimize operator actions and satisfy requirements of APR1400 emergency operation procedure (EOP), the SGs Atmospheric Dump Valve (ADV) opening ratio, auxiliary feed water (AFW) and outside cooling water injection flow rates were investigated to have suitable values. The analysis results would be useful for performing the experiment to verify the APR 1400 extended SBO optimum mitigation strategy using outside cooling water injection.

Influence of facial hair length, coarseness, and areal density on seal leakage of a tight-fitting half-face respirator

ABSTRACTBackground: OSHA regulations state that an employer shall not permit tight-fitting respirators to be worn by employees who have facial hair that comes between the skin and facepiece seal. Studies have shown that facial hair in the face seal zone can increase penetration and decrease the fit factor (FF), although the relationship between the amount and characteristics of facial hair and the increase in penetration is not well quantified. This article examines the influence of facial hair length, areal density, and coarseness on FF for one model of half-face elastomeric negative-pressure air purifying respirator.Approach: Quantitative fit tests (QNFT) were performed on 19 subjects with beards initially 0.500-in long and subsequently trimmed to 0.250, 0.125, and 0.063 in, then after a razor shave. Three fit tests were performed at each of the 5 lengths, for 285 total tests. The average diameter and areal density of cheek and chin hair were measured. Penetration was modeled as a function of hair length category, beard areal density, and hair coarseness.Results: FF decreased with beard length, especially beyond 0.125 in. However, passing FF scores were achieved on all tests by all subjects at the smooth shave and 0.063 in conditions, and 98% of tests were passed at 0.125 in; seven subjects passed all tests at all conditions. Chin and cheek areal densities were significantly different and were only weakly correlated. Beard hair diameters were normally distributed across subjects (mean 76 µm, standard deviation 7.4 µm). Beard length and areal density, but not coarseness, were statistically significant predictors of fit using an arcsine transformed penetration model. FF decreased with increasing beard length, especially beyond 0.125 in, although FF with a “stubble” beard did not differ significantly from a smooth shave. FF also decreased with increasing areal beard hair density.Conclusion: Beard length and areal density negatively influence FF. However, tight-fitting half-face negative-pressure respirator fit tests can achieve adequate fit factor scores even with substantial facial hair in the face seal area.

Interfacial leakage of elastomer seals at low temperatures

Interfacial leakage of air in hydrogenated nitrile butadiene rubber (HNBR) O-ring seals exposed to sub-ambient temperatures is studied. Flange-type fixtures with sealing surfaces produced by 3 different surface finish processes are used. When the seals are cooled down to temperatures below the elastomer glass transition point Tg of (−23 °C), an abrupt increase of air leakage (>10−2cm3/min) is observed. The effects of surface finish conditions, compression ratio, grease lubrication and additions of carbon black in the HNBR on the cold leakage are discussed. Persson's contact mechanics and effective medium leakage theory coupled with finite element analysis (FEA) of the HNBR seals are utilized to capture the changes in the contact area and pressure with cooling and predict the seal failure temperatures. The main cause for the cold seal failures is believed to be the detachment of the elastomer seals from their mating sealing parts due to the elastomer thermal contraction and the negligible recovery of the HNBR in cold environment. In addition, the adhesive rubber-substrate interface influences the detachment and seal failure.

Characterisation of turbine behaviour for an engine overspeed prediction model

This paper focuses on the characterisation of turbine overspeed behaviour to be integrated into an engine overspeed model capable of predicting the terminal speed of the high pressure turbine (HPT) in the event of a high pressure shaft failure. The engine considered in this study features a single stage HPT with a shrouded contra-rotating rotor with respect to the single stage intermediate pressure turbine (IPT). The HPT performance is characterised in terms of torque and mass flow function for a range of expansion ratios at various non-dimensional rotational speeds (NH), up to 200% of the design value. Additionally, for each HPT expansion ratio and NH, the change in capacity of the downstream IPT, for different IPT non-dimensional rotational speeds (NI), also needs to be characterised due to the extremely positive incidence angle of the flow from the upstream rotor. An automated toolkit is developed to generate these characteristic maps for both the HPT and IPT.An unlocated high pressure shaft failure will result in rearward movement of the rotor sub-assembly. This causes changes in the rotor tip and rim seal regions, and in the rim seal leakage flow properties. Therefore, in the present work, a high fidelity characterisation of turbine behaviour with the inclusion of tip and rim seals is carried out at three different displacement locations, 0 mm, 10 mm and 15 mm, to improve terminal speed estimation. Furthermore, there is a possibility of damage to the tip seal fins of the HPT rotor due to unbalance in the spool that may result in contact between the rotor aerofoil tip and the casing. Consequently, another set of characteristics are generated with damaged tip fins at each displacement location.It is observed from the characteristics that the torque of the HPT rotor decreases with increasing NH. The HPT mass flow function initially decreases and then increases with an increase in NH. The IPT mass flow function initially remains similar and then decreases with increase in NH above values of 150%. The HPT rotor torque and IPT mass flow function decrease with rearward movement of the HPT rotor sub-assembly for all values of NH. With worn tip seal fins all parameters mentioned previously are lower than in the nominal undamaged case. The high fidelity characterisation of turbines that follows the sequence of events after a shaft failure, as described in this work, can provide accurate predictions of terminal speed and thus act as a tool for testing design modifications that can result in better management and control of the over-speed event.

Numerical Investigation on the Leakage and Static Stability Characteristics of Pocket Damper Seals at High Eccentricity Ratios

Annular gas seals for compressors and turbines are designed to operate in a nominally centered position in which the rotor and stator are at concentric condition, but due to the rotor–stator misalignment or flexible rotor deflection, many seals usually are suffering from high eccentricity. The centering force (represented by static stiffness) of an annular gas seal at eccentricity plays a pronounced effect on the rotordynamic and static stability behavior of rotating machines. The paper deals with the leakage and static stability behavior of a fully partitioned pocket damper seal (FPDS) at high eccentricity ratios. The present work introduces a novel mesh generation method for the full 360 deg mesh of annular gas seals with eccentric rotor, based on the mesh deformation technique. The leakage flow rates, static fluid-induced response forces, and static stiffness coefficients were solved for the FPDS at high eccentricity ratios, using the steady Reynolds-averaged Navier–Stokes solution approach. The calculations were performed at typical operating conditions including seven rotor eccentricity ratios up to 0.9 for four rotational speeds (0 rpm, 7000 rpm, 11,000 rpm, and 15,000 rpm) including the nonrotating condition, three pressure ratios (0.17, 0.35, and 0.50) including the choked exit flow condition, two inlet preswirl velocities (0 m/s, 60 m/s). The numerical method was validated by comparisons to the experiment data of static stiffness coefficients at choked exit flow conditions. The static direct and cross-coupling stiffness coefficients are in reasonable agreement with the experiment data. An interesting observation stemming from these numerical results is that the FPDS has a positive direct stiffness as long as it operates at subsonic exit flow conditions; no matter the eccentricity ratio and rotational speed are high or low. For the choked exit condition, the FPDS shows negative direct stiffness at low eccentricity ratio and then crosses over to positive value at the crossover eccentricity ratio (0.5–0.7) following a trend indicative of a parabola. Therefore, the negative static direct stiffness is limited to the specific operating conditions: choked exit flow condition and low eccentricity ratio less than the crossover eccentricity ratio, where the pocket damper seal (PDS) would be statically unstable.

A leakage channel model for sealing interface of mechanical face seals based on percolation theory

Abstract Leakage channels of contact mechanical face seals have significant influence on sealing performance. The porosity of initial sealing interface is obtained based on the fractal parameters of rotating and stationary rings firstly. The effects of fractal parameters, material properties and face pressure on porosity of sealing interface are revealed, and then the percolation assumption for single grid model of sealing interface is proposed. Finally, a leakage channel model based on the volume porosity of sealing interface is established and investigated accordingly. The proposed research is expected to provide the basis for the explanation of leakage and optimum design of contact mechanical face seals.