Seal Leakage Research Articles

Numerical investigation of the labyrinth leakage flow on the performance of a compressor cascade

This paper examines the effect of labyrinth seal structure on the evolution of vortex systems and the performance of the cascade. It is found that the labyrinth seal leakage leads to the circumferential development of the separation vortex, and the axial influence region of the concentrated shedding vortex also expands, which increases the flow loss and reduces the diffuser capacity. Among all the cases, the deteriorating effect of the cavity without a labyrinth seal is the most significant. This results in an 83% increase in total pressure loss compared to the prototype cascade. The straight tooth labyrinth and the straight tooth labyrinth with block structures can effectively reduce the leakage from the sealing cavity and weaken the deterioration caused by labyrinth seal leakage. Among these schemes, the straight tooth with block scheme has the most considerable effect, resulting in a 19% reduction in total pressure loss. As the incidence angle increases, the recirculation zone on the end wall of each scheme gradually shrinks toward the leading edge. Meanwhile, the static pressure rises, and the velocity decreases near the leading edge. Compared with the straight tooth scheme, the straight tooth with block scheme can reduce the high-loss zone by 14% at most. In addition, as the sealing clearance gradually increases, the inhibitory effect of the straight tooth with block scheme on the deterioration of cascade performance caused by the labyrinth sealing cavity is gradually enhanced compared to the straight tooth structure. The improvement effect is optimal under 0.5 mm sealing clearance.

Leakage Characteristics and Experimental Research of Staggered Labyrinth Sealing

The staggered labyrinth seal is widely used in aerospace, transportation, mining, and other fields due to its advantages of adapting to high speed, reliable sealing performance, and low or even frictionless friction between dynamic and static rotors. The traditional calculation method of labyrinth seal leakage mostly focuses on the fact that the internal medium is an ideal gas and only considers a single effect, which cannot accurately describe the leakage of liquid medium lubricating oil in the labyrinth seal. Therefore, this study focuses on the leakage characteristics of labyrinth seals, and it proposes a leakage calculation method based on liquid medium in view of the shortcomings of existing calculation methods under liquid medium conditions. By considering the thermodynamic and frictional effects of the staggered labyrinth sealing, the resistance loss and thermodynamic effect of the lubricating oil in the sealing cavity were analyzed. The flow field analysis was used to reveal the leakage law of lubricating oil under different conditions, and the factors such as total inlet pressure, spindle speed, and sealing clearance were considered. Finally, the leakage characteristics of the staggered labyrinth seal and the accuracy of the calculation method of the leakage of the staggered labyrinth seal under multiple effects were revealed through experimental verification. This study provides useful guidance for the performance optimization of labyrinth seals in practical applications.

Multi-Physical Field, Coupled, Mixed Lubrication Analysis of Hydraulic Reciprocating Vacuum Lip Seal

Engineering practice has demonstrated that seal failure can result in severe leakage and wear, reducing the efficiency of hydraulic systems and even leading to major safety risks. Currently, analyses of the thermal aspect of seal interfaces are relatively limited, with most studies focusing on mechanical analysis. However, in actual applications, temperature has a significant impact on sealing performance. In this paper, nonlinear elastomechanics, viscous fluid mechanics, micro-contact mechanics, micro-deformation theory, and thermodynamics are coupled to establish a mixed lubrication model considering the thermal effect. The reliability of the mixed lubrication model is verified through experiments, and the temperature distribution of the oil film in the sealing area and the temperature distribution of the seal ring are simulated. Finally, the effects of the reciprocating speed, root mean square roughness, fluid medium pressure, and seal pre-compression on seal friction force and leakage are investigated. The results show that the heat generated in the sealing area accumulates at the bottom of the V-ring. Under the same conditions, compared with the instroke, the temperature-rise area of the outstroke is biased to the left and the increase in temperature is greater. In addition, the piston rod speed and the preliminary compression of the seal ring have a greater impact on the overall seal friction force and leakage. Under a lower seal pre-compression, the RMS roughness has a great influence on the leakage and friction in the outstroke, while the impact of the internal stroke is limited.

Experimental Investigation on Leakage and Frictional Heat Generation Characteristics of Low Hysteresis Brush Seals

Abstract Low hysteresis brush seals are frequently used in systems operating at a high speed in environments featuring a high temperature and pressure. The high-speed rotor comes into contact with the bottom end of the bristles of the brush seal in such scenarios to generate a significant amount of frictional heat, which directly affects its sealing performance and service life, while a high temperature can increase the magnitude of its friction-induced heat. In this study, we report the cyclical testing of a low hysteresis brush seal while increasing and decreasing the speed of the rotor under varying differences in the pressure and temperature. We focus on the characteristics of leakage, hysteresis effect, and temperature rise at the bottom end of the bristles of the brush seal owing to frictional heat. The results showed that the volume of leakage increased at a high temperature under a strong hysteresis effect and a small rise in the temperature. Moreover, as the speed of the rotor exceeded 6000 rpm, the temperature of the system increased rapidly owing to frictional heat. During the speed decrease stage, the temperature rise decreased sharply and then gradually until it became nearly constant. The hysteresis effect resulted in a lower temperature rise during the decrease in the speed of the rotor compared with that during an increase in its speed. While the low hysteresis structure can effectively reduce hysteresis effect compared with that of the conventional brush seal, it induced greater leakage. It is necessary to choose a pressure relief chamber of a suitable size to minimize leakage. Furthermore, the low hysteresis brush seal exhibited a smaller friction temperature rise than the conventional seal, where this is beneficial for its service life.

A study on radial oil seal leakage failure due to viscoelasticity under dynamic eccentricity

Purpose This study aims to investigate the causes of leakage in radial oil seals under dynamic eccentricity, elucidate the influence of operating parameters on leakage failure and develop methods for predicting and preventing such leakage. Design/methodology/approach Based on the principle of cam motion and considering viscoelasticity, develops a motion model of the compression and release of the shaft seal and proposes a method to determine its failure. In addition, this study quantifies the leakage gap and formulates a quantitative calculation model to accurately determine the location and shape parameters of the leakage gap. Findings Leakage gaps predominantly occur during the release phase of the shaft seal. Their presence can be identified by comparing the descending times of the seal and the shaft during this phase. An increase in rotation speed and eccentricity heightens the likelihood of gap formation, with both the dimensions and leakage rate of the gap increasing as these factors escalate. Eccentricity, in particular, has a more pronounced effect on gap formation. Originality/value This study clarifies the failure mechanisms of radial oil seals under dynamic eccentricity and introduces a criterion for identifying leakage gaps, providing valuable theoretical guidance for the design and optimization of radial oil seals. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-05-2024-0192/.

Tangential contact modeling to seal considering elastic-plastic for lubrication transition mechanism

Researches on the reciprocating seals lubrication under elastic-hydrodynamic lubrication (EHL) are mature, and leakage of failure criterion has been described with Couette flow for more than 30 years, which could not reflect to leakage mechanism in multiscale. Thus, it is necessary to explore seal leakage failure to focus on micro convex bodies of asperities model under contact pressure and cycle tangential friction stress in mixed lubrication. This is because convex bodies behaviors determine sealing effect and lubrication behaviors in microscale with subjecting to the dominant pressure. Interaction between convex bodies fatigue hysteresis curve and elastic-plastic strain are also calculated to explore sealing effect with leakage rate mechanism. We then design water seal at high pressure of 100 MPa with the speed of 0.1–1 m/s and medium temperature from 5 ℃ to 40 ℃. IWAN model of the convex bodies are calculated. Probability density function and Jenkin’s elements critical slip displacement are obtained. Convex bodies of radial and tangential deformation are also calculated through loading of contact pressure and friction stress with cycle strength coefficient to obtain seal fatigue lifespan. Ratio to seal stick and slip friction is calculated for evaluating the loading boundary. Seal leakage failure mechanism with fatigue characteristics is illustrated with macro lubrication parameters and micro convex bodies mechanics performance.

Quantitative assessment of double-cone seal leakage in canned reactor coolant pump based on double-cone ring stress

The double-cone seal is a crucial component of the canned reactor coolant pump (RCP), serving as a vital barrier to prevent coolant leakage. Its sealing status directly impacts the operational safety of the RCP. Given the intricate operational conditions and rigorous sealing requirements of RCP, there is a dearth of effective detection methods for minor leakage of double-cone seal. To address this issue, a quantitative assessment method for the leakage of double-cone seal based on double-cone ring stress is proposed. In this paper, the functional relationship between the double-cone ring stress and the specific pressure of the gasket seal is first derived. Subsequently, a leakage rate assessment model based on the double-cone ring stress is proposed by combining with the leakage rate expression of the metal gasket connection structure. Finally, the feasibility of the proposed method for the leakage detection of double-cone seal is verified by finite element simulation and leakage simulation test. The results demonstrate that the proposed method is capable of detecting small leakage conditions with a leakage rate in the order of 1 × 10−4 cm3·s−1, which is sufficient for the micro-leakage detection of double-cone seal.

Prediction models for seal performance of a space seal considering atomic oxygen effects

A low impact docking system with advanced capabilities has been developing for future spacecrafts, and its main interface docking seal (MIDS) is both a critical component and a research topic of interest. It is a typical design for the MIDS that adopts the elastomer seal-on-seal structure made of silicone rubbers, and the atomic oxygen (AO) in space had been found to take great effects on the sealing performance by previous experimental studies, especially for the seal leak, seal adhesion, and compression set. Exposure to AO may cause obvious changes on the sealing surface of the MIDS, and some characteristic parameters of morphology are proposed to characterize the changes in this study, including of the porosity, roughness and radius of curvature. Both the leakage model and the adhesion model of the MIDS are further developed to predict the sealing performance considering AO effects, which had been confirmed by the application experiments. The experimental data are in good agreement with the calculation data. The effects of AO on the sealing performance are simulated and analyzed by the proposed prediction models. The results are beneficial to the developments of the MIDS and other space seals.

Fault diagnosis method and experimental research of reciprocating seal based on CFD-GAN-AE

Abstract Hydraulic impactors are crucial for oil and gas exploration, but seal failure is a common issue, having an effective technique for diagnosing sealing faults can provide dependable operational and maintenance assistance for Hydraulic impactors. However, identifying wear failures is challenging and there is limited data available, there has been significant interest in intelligent defect diagnosis technology that is based on deep learning in recent years. Therefore, we propose a method to enhance the data and identify faults through deep learning. Initially, the CFD method was used to simulate seal leakage and determine whether factors such as pressure can indicate varying levels of leaking in the seal, this approach provides a theoretical foundation for signal gathering experiments. Next, the EMD approach is used to separate the non-smooth pressure signal from the seal experiment, revealing fault features that indicate the extent of leakage. Finally, the improved GAN method is suggested to balance imbalanced samples by utilizing the sample overlap rate, it is paired with the AE algorithm to categorize different levels of leakage. Furthermore, a comparative analysis is conducted between the proposed methodology and several classical fault diagnosis methods. This work investigates seal damage through the lens of computational fluid dynamics and the fault identification of uneven seal samples is accomplished.

A comparison of static and rotordynamic characteristics for two types of liquid annular seals with and without helical grooved stator

Less leakage is a benefit of parallel grooved liquid seals (labyrinth seals). But researches show that the liquid seal with parallel grooves on the rotor harms the rotor stability. The seal with helical grooves on stator performs well in terms of rotordynamics, and its leakage is sensitive to the rotating speed. To make use of the advantages of both seals and improve seal stability, based on the Smooth-stator/Parallel Grooved-rotor (SPG) liquid seal, a Helical Grooved-stator/Parallel Grooved-rotor (HGPG) liquid seal is designed. To evaluate two liquid seals’ leakage, rotordynamic characteristics and drag power loss, a transient computational fluid dynamics-based method is employed. This method is based on the multi-frequency elliptical-orbit rotor whirling model and the mesh deformation technique. The published experimental data of the leakage and rotordynamic force coefficients for an SPG liquid seal are used to validate the accuracy and dependability of the current method. Seal leakage and force coefficients are presented and compared for the SPG liquid seal and the HGPG liquid seal at various pressure drops. The influences of parallel groove depth on the leakage and rotordynamic properties for the HGPG liquid seals at two rotational speeds (2000, 6000 r/min) are analyzed. The numerical findings demonstrate that the novel HGPG liquid seal has a lower leakage flow rate (by ∼22.3%) than the traditional SPG liquid seal. There is an optimal parallel groove depth that minimizes leakage. The presented novel HGPG liquid seal significantly improves rotordynamic stability, due to the similar effective stiffness and the obviously larger positive effective damping. Reducing parallel groove depth can increase the positive effective damping. In terms of leakage and rotordynamic characteristics, the novel HGPG liquid seal is a better seal design for liquid turbomachinery.

Failure analysis and structural improvement of helicopter landing gear seals based on experiments and three-dimensional numerical simulation

The utilization of O-ring seal structures in landing gears has historically been associated with high rates of failure. Therefore, this study analyzes helicopter landing gear friction failures based on experimental and numerical simulations. The model is designed to replicate the failure phenomena including “seal extrusion”, “seal leakage”, “seal wear”, and “seal distortion”, and to further investigate causes of failure. Corresponding failure criteria are also presented. Addressing the deficiencies inherent in the original O-ring structure, three composite seal structures—namely, the VL seal, double triangle seal, and T-seal—are introduced to enhance the respective seal structure of the buffer pillar. The findings exhibit that, following the transition to the composite seal structure, the strain peaks are optimized. Finally, this paper offers optimal contact pressure ranges for the optimized seals.

Effect of surface topography and roughness on the leakage of static seals

Static seal is widely used in modern machinery. Leakage of static seals would shorten the mechanical system’s service life and affect the environment. To understand the leakage characteristics of static seals, in this work, an experimental apparatus for leakage quantization was built. The effects of surface topography and roughness on the leakage performance of static seals subject to elevated pressure were highlighted. It was found that the leakage rate is negatively correlated with contact pressure. Orientation of surface topography affects the leakage, where the grinding scar parallel to the leakage direction contributes to the leakage, and the perpendicular grinding scar has an inhibiting effect. The leakage rate of irregular and discontinuous surface topography is lower than that of regular ones, and it increases with increasing surface roughness. Furthermore, the leakage mechanism of surface topography and roughness was revealed. This work provides general guidance for the parameters design of static seals.

Investigation of static and rotordynamic characteristics of the segmented annular seals based on the differential quadrature method

Theoretically, a solution model for the static and rotordynamic characteristics of a segmented annular seal based on the local differential quadrature (LDQ) method was established. The impacts of node density and the number of local support domain nodes on the accuracy of the algorithm were analyzed. A test rig for the leakage of segmented annular seals was designed and built. The leakage results measured on the test rig were compared with the theoretical analysis results to demonstrate the accuracy of the local differential quadrature method. The influence of structural and operating parameters on the seal static and rotordynamic characteristics was analyzed Based on the work carried out above. The research results indicate that when the number of local support domain nodes is equal to 3, the static and rotordynamic characteristics of the segmented annular seal can be obtained accurately based on the solution model. As the rotational speed increases, the segmented annular seal’s lift force, leakage, stiffness coefficient, and damping coefficient increase. As the pressure ratio increases, the lift force and leakage of the segmented annular seal significantly increase while the stiffness and damping coefficients decrease. As the depth and width of the pocket increase, the lift force, stiffness coefficient, and damping coefficient of the segmented annular seal first increase and then decrease. As the length of the pocket increases, the lift force, stiffness coefficient, and damping coefficient of the segmented annular seal increase. The influence of the pocket depth, width, and length on the leakage is minimal.

ВЛИЯНИЕ УСЛОВИЙ ХРАНЕНИЯ АВТОБУСОВ В КРЫТЫХ ОТАПЛИВАЕМЫХ СТОЯНКАХ НА ИНТЕНСИВНОСТЬ КОРРОЗИОННОГО ИЗНАШИВАНИЯ КУЗОВОВ

The efficiency of the rolling stock of road transport is determined by both the efficiency of organizing transport work and the cost of ensuring the operability of vehicles. One of the current problems with the operation of buses is the corrosive destruction of their bearing structure, which leads to both a reduction in the operating time of vehicles and an increase in the operating costs associated with the overhaul of bodies. During the work, it was revealed that the main reasons for the intensive corrosion destruction of bus bodies are insufficient corrosion resistance of metals that are used in the manufacture of the body frame. The main places of occurrence of body corrosion foci are: wheel arches; rear and lower parts of the bus, which are more affected by adverse road conditions; upper and lower parts of window openings in case of seal leakage. Studies were conducted on the temperature and relative humidity of the indoor heated bus parking area in winter. Based on the results of the study, dependencies were obtained: air temperature in the indoor parking room from ambient temperature, relative air humidity in the indoor parking room from relative ambient air humidity, relative air humidity in the indoor parking room and ambient temperature. The nature of air exchange between the parking room and the environment has been established. According to the results of the study, factors contributing to the intensive corrosive destruction of bus bodies were established.

Lung-Mimetic Hydrofoam Sealant to Treat Pulmonary Air Leak.

Pulmonary air leak is the most common complication of lung surgery, contributing to post-operative morbidity in up to 60% of patients; yet, there is no reliable treatment. Available surgical sealants do not match the demanding deformation mechanics of lung tissue; and therefore, fail to seal air leak. To address this therapeutic gap, a sealant with structural and mechanical similarity to subpleural lung is designed, developed,and systematically evaluated. This "lung-mimetic" sealant is a hydrofoam material that has alveolar-like porous ultrastructure, lung-like viscoelastic properties (adhesive, compressive, tensile), and lung extracellular matrix-derived signals (matrikines) to support tissue repair. In biocompatibility testing, the lung-mimetic sealant shows minimal cytotoxicity and immunogenicity in vitro. Human primary monocytes exposed to sealant matrikines in vitro upregulate key genes (MARCO, PDGFB, VEGF) known to correlate with pleural wound healing and tissue repair in vivo. In rat and swine models of pulmonary air leak, this lung-mimetic sealant rapidly seals air leak and restores baseline lung mechanics. Altogether, these data indicate that the lung-mimetic sealant can effectively seal pulmonary air leak and promote a favorable cellular response in vitro.

Insights Into Frictional Brush Seal Hysteresis

Abstract Brush seals offer a superior sealing effectiveness compared to labyrinth seals. However, widespread use of brush seals is constrained by deleterious behaviors such as pressure-stiffening and hysteresis. For the latter, the bristles bend during the shaft incursion process and do not fully recover during the shaft retraction process. An opening gap is created, which increases seal leakage unless the pressure load drops to a certain level. In this work, analytical and numerical models based on a single bristle are proposed to capture the seal's response to shaft displacement with and without pressure loading. The models are validated using static stiffness tests at an unpressurized condition from literature. The main results show that modeling of the backing ring friction is essential to capture the bristle hang-up behavior. Shaft friction dominates at unpressurized conditions, while backing ring friction dominates at high pressure loading. An expression for shaft hang-up displacement has been derived. A sensitivity study shows that seals with shallow lay angle, short bristle length, and large bristle diameter are less prone to hang-up problems. The models developed in the present framework have been shown to qualitatively capture the pressure stiffening, hysteresis, bristle hang-up, and shaft rotation effects.

Investigation on the influence of seal clearance leakage on the rotating stall characteristics for a centrifugal pump

The occurrence and development of centrifugal pump rotating stall is closely related to disturbance in the incoming flow. The seal clearance leakage is an inherent disturbance in the impeller incoming flow of centrifugal pumps. In order to investigate the seal clearance leakage influence on the rotating stall characteristics, the flow field numerical simulation of a centrifugal pump under rotating stall flow conditions with and without seal clearance are carried out. It is found that under the 0.4Q0 rotating stall condition with seal clearance leakage, the “λ” special shaped high-velocity region distribution along the blade leading edges are strengthened, which lead to larger scale of stall vortices. And the periodicity of the separation vortex evolution is more obvious under the condition with leakage. For a specific stall vortex development process, at the initial format stage, there is a notable disturbance characteristic of medium frequencies band that of 2–3 times the rotation frequency in the pressure fluctuation near the blade leading edges, which is significantly different from that under the condition without leakage. The vorticity analysis shows that this disturbance is closely related to the leakage induced vortices. Affected by the seal clearance leakage disturbance, the stall rotating propagation frequency is reduced from 0.143 times the impeller rotational frequency to 0.103 times. Meanwhile, the fluctuation intensity in the impeller channels is greatly enhanced. Therefore, by judging the special fluctuation frequencies, regularity, and intensity trend in the monitoring signal, it can not only be used to guide the safe operation of centrifugal pumps under off-design conditions but also serve as the basis for judging the wear of the seal, which has important practical significance.

Influence of Different Head and Neck Positions on Oropharyngeal Leak Pressure with the LMA Protector Airway: A Cross-over Study

Introduction: The assessment of seal pressure or leak pressure in supraglottic devices has commonly been used to confirm device functionality and for research purposes regarding laryngeal mask airways (LMAs). When used for controlled ventilation, the LMA Protector provides a better oropharyngeal seal pressure. Materials and Methods: In this cross-over study, thirty-five patients of either sex, aged 18 to 70 years, American Society of Anaesthesiology (ASA) class I and II, with a weight range of 50-70 kg, scheduled for elective surgery under general anaesthesia where a supraglottic airway device was indicated, were enrolled. In all 35 patients, the position of the patient’s head and neck was changed from neutral to flexion, extension, and right and left lateral rotation. The primary objective of the study was to compare the differences in oropharyngeal leak pressure (OLP) with changes in head and neck positions using the LMA Protector airway device. Results: The mean age of the participants was 42.26 years, and the average weight was 63.34 kg. The LMA Protector was placed in 18 females and 17 males. A Mallampati grade of I was noted in 16 patients, while a grade of II was observed in 19 patients. The OLP achieved in this study was higher, providing adequate ventilation and oxygenation in all positions. The OLP and tidal volume in flexion were higher compared to the seal pressure in the neutral position (31.89 cm H2O, SD 5.080 cm H2O vs. 34.49 cm H2O, SD 4.804 cm H2O, p<0.05). No significant difference in OLP was observed when changing to different head positions, i.e., in extension, right lateral, and left lateral positions. Conclusion: The LMA Protector is an effective device in terms of achieving high oropharyngeal seal pressure. It produced better oropharyngeal seal pressure in the flexion position compared to the neutral position.

Leakage performance of hybrid brush seals under high differential pressure conditions

A three-dimensional axial fluid-porous medium-flow field model was designed for the sealing properties of the hybrid brush seal (HBS) seal structure under complex operating conditions. Using a computational fluid dynamics model in view of non-Darcy porous media, the pressure and velocity distributions of the sealing medium in the flow path were simulated, and the flow characteristics of the hybrid brush seal were analysed to obtain the leakage of the hybrid seal structure. The results show the implication of pressure ratio (Rp) on the labyrinth brush seal leakage rate and pressure distribution. Compared with typical brush seal test results, as the inlet and outlet pressure ratio (Rp) increases, the more obvious the hybrid brush seal sealing effect is, when the pressure ratio is 3 bar, the spillage of the hybrid brush seal is reduced by about 39%.

Thermo-economic analysis of regenerative supercritical CO2 Brayton cycle considering turbomachinery leakage flow

The regenerative supercritical CO2 Brayton cycle (RSCBC) has great potential to improve the energy utilization efficiency and reduce greenhouse gas emissions. The leakage of supercritical CO2 into rotor cavity through labyrinth seals in turbomachinery including turbine and compressor inevitably reduces the cycle efficiency. Here, we propose a numerical method coupling the thermodynamic model with the labyrinth seal leakage model. The variations of turbomachinery leakage flow with cycle parameters and its effect on cycle thermo-economic performance are investigated. The optimal cycle parameters and thermo-economic performance are obtained by the multi-objective optimization. We find the cycle maximum pressure benefits the thermo-economic performance, while penalizes the sealing performance of turbomachinery labyrinth seal. Compared with ignoring the turbomachinery leakage, the optimal inlet state of the compressor vicinity of the pseudo-critical point that is adjacent to critical point when considering turbomachinery leakage. Furthermore, the turbomachinery leakage flow accounted for 2.5 % of the total flow under the optimized working condition, causing the thermal efficiency and exergy efficiency decrease 1.38 % and 3.52 % respectively, the heat exchanger area per unit power output and levelized energy cost increase 3.8 % and 3.83 % respectively. The proposed method and obtained results can provide some guidance for the optimal design of RSCBC system.