Seal Teeth Research Articles

Turbomachines seal flow resistance enhancement and leakage reduction based on flow control method with bow-shaped auxiliary teeth

Improving sealing performance without clearance reduction is important for the economic and safety operation of modern turbomachines. For this purpose, this study proposes the bow-shaped auxiliary teeth to reduce the leakage. One bow-shaped auxiliary tooth is installed after each seal tooth to guide the leakage jet towards the side wall of seal tooth. Then the leakage jet attaches itself to the inner wall of cavity. The Computational Fluid Dynamics method is used to calculate the flow field in the new seal. Results show that flow impingements, flow deflections, and enhanced vena contraction effect increase the leakage flow resistance and reduce the leakage velocity. The application of the bow-shaped auxiliary teeth reduces the leakage flow rate by 43.8–46.3 % compared with the labyrinth seal. Geometry parameters analysis shows that reducing the axial distance between seal tooth and bow-shaped auxiliary tooth, and increasing the central angle of bow-shaped auxiliary tooth are beneficial for leakage reduction. With the increase in the radius of bow-shaped auxiliary tooth, the leakage firstly decreases and then changes a little.

Preswirl control and rotordynamic stability improvement of turbomachine seal equipped with newly designed spiral steering blades

In turbomachine seal, preswirl generates the tangential force that induces the rotor vibration. Effective preswirl control can improve the rotordynamic stability. For this purpose, this study designs the spiral steering blades in front of the first seal tooth. Adjacent spiral steering blades form one spiral channel. The fluid is constrained and guided to flow along the spiral channel. The CFD results show that the new design reduces the leakage due to the additional throttling. The new design reverses the preswirl direction, optimizes the circumferential pressure distribution, and generates the negative tangential force. More spiral steering blades are better to reduce the tangential force. The new design largely reduces the effect of preswirl, and performs well under high preswirl condition.

Advances and prerequisites for strontium isotope analyses through laser ablation in an aquatic context – Targeting Mid-Neolithic Baltic Sea harp seal (Pagophilus groenlandicus) mobility and breeding grounds

Harp seals (Phoca groenlandicus), once present in the Baltic Sea, now stand extinct. During the Middle Neolithic period, they held significant dietary importance for the Pitted Ware Culture hunter-fisher-gatherers in Scandinavia. Because they are no longer available for ecological studies, little is known about their specific behavioural intricacies, such as diet, mobility, and reproductive strategies. Because of the seal's pivotal role in these human societies and because they provide an interesting ecological case study on post-isolation ecological adaptation to new environmental conditions, a comprehensive investigation into Baltic Sea harp seal behaviour is warranted.In this pursuit, we employ sequential analysis of strontium isotope ratios (87Sr/86Sr) in harp seal teeth sourced from archaeological contexts across three study regions. This data is harmonized with osteometric analyses from fifteen archaeological sites from the Baltic Sea area, establishing a methodological framework for comprehending the Sr isotopic pathway in a brackish water inland sea. By adopting this approach, we unveil breeding and mobility patterns of the long-extinct Baltic Sea harp seals, approximate specific breeding areas connected to each group of seals and delve into the ontogenic temporal frame governing these observed patterns. This endeavour culminates in an enriched understanding of the adaptive behaviours exhibited by Baltic Sea harp seals and equips us with the insights necessary to decipher the lifestyle of the human societies intricately intertwined with them.

ON THE USE OF PSP TO DETERMINE THE RIM SEALING EFFECTIVENESS

Abstract The control of cavities sealing has been a challenging problem since early gas turbine development stages and several aspects regarding the flow physics and the modelling of rim seal flows still represent an open question. Fundamental test cases have been used in the open literature to characterize the level of ingestion by varying the main flow parameters and the geometrical features. In most of them, the effectiveness is measured by using taps connected to a gas analyzer used to sample the concentration of a foreign gas on the stator surface used to seed the purge flow. Consequently, the results are usually single point measurements, unsteady effects are inevitably neglected, the intrusiveness of the approach must be carefully checked and the application on the rotor side demands for complex slip-rings or telemetry. To overcome these limitations, the current work presents the application of the PSP technique to the study of hot gas ingestion phenomena on a single stage rotating cold rig. The 2D distributions of partial pressure of oxygen collected through the wide optical accesses present in the rig were then related to the seal effectiveness. The proposed methodology was firstly validated through a comparison with the data obtained from standard gas sampling and then applied as main experimental technique. The analysis of the results highlighted the capabilities of the PSP to fast collect data on both stator and rotor side, including the tip of the seal tooth where non uniform efficiency distributions in the circumferential direction have been detected.

Oil-Sealing Performance Evaluation of Labyrinth Seal Using Combined Finite Element Analysis and Computational Fluid Dynamics

Mechanical seals, such as labyrinth seals, are typically installed at the turbine outlets to prevent oil leakage. However, these seals undergo deformation because of the vibrations of the rotor, even during normal turbine operating conditions, which may cause an increase in oil leakage. In this study, the oil leakage performance of three labyrinth seals with different types of seal teeth, narrow stainless teeth (Type 1), wide aluminum teeth fixed on the body (Type 2), and fixed wide aluminum movable teeth (Type 3), were evaluated using finite element (FE) and computational fluid dynamics (CFD) analyses. Three-dimensional FE models of the rotor and oil deflectors were developed, and the plastic deformation of the teeth of the labyrinth seals was predicted when the rotor impacted the sealing teeth during turbine operation. The oil leakage was predicted using CFD analysis. The results indicated that the Type 3 seal, including movable teeth, is beneficial in preventing leakage and tooth deformation compared with the other types. The Type 2 seal is advantageous because it results in a smaller increase in gap size and greater vena contracta effects than the Type 1 seal. The results of this study could be helpful when designing and selecting the teeth of a labyrinth seal.

Multi-decadal trends in biomarkers in harp seal teeth from the North Atlantic reveal the influence of prey availability on seal trophic position.

Arctic food webs are being impacted by borealisation and environmental change. To quantify the impact of these multiple forcings, it is crucial to accurately determine the temporal change in key ecosystem metrics, such as trophic position of top predators. Here, we measured stable nitrogen isotopes (δ15 N) in amino acids in harp seal teeth from across the North Atlantic spanning a period of 60 years to robustly assess multi-decadal trends in harp seal trophic position, accounting for changes in δ15 N at the base of the food web. We reveal long-term variations in trophic position of harp seals which are likely to reflect fluctuations in prey availability, specifically fish- or invertebrate-dominated diets. We show that the temporal trends in harp seal trophic position differ between the Northwest Atlantic, Greenland Sea and Barents Sea, suggesting divergent changes in each local ecosystem. Our results provide invaluable data for population dynamic and ecotoxicology studies.

Detailed Simulations of a Three-Stage Supercritical Carbon Dioxide Axial Compressor with a Focus on the Shrouded Stator Cavities Flow

This paper describes the findings of detailed simulations performed to investigate the impact of seal teeth cavity leakage flow on the aerodynamic and thermal performance of a three-stage supercritical CO2 axial compressor. The study compares a shrouded stator configuration (with cavities) to a cantilevered stator configuration (without cavities) to highlight their differences. High-fidelity computational fluid dynamics simulations were performed using non-linear harmonic (NLH) and mixing plane assumptions, considering various possible rotor/stator interface configurations for mixing plane calculations. The key performance parameters for each case were compared, and the best-performing configuration selected for further analysis. The individual stage performance parameters are also examined and compared between the cantilevered and shrouded configurations. It was observed that in the shrouded case, the leakage flow enters the cavity downstream of the stator trailing edge and gets entrained into the primary flow upstream of the stator, leading to boundary layer changes at the hub and degradation of stator and downstream rotor performance. Vortical flow structures were also observed in the stator wells, which tended to change the flow angles around the region, thereby affecting mixing and velocity distribution, resulting in a slight deterioration of compressor performance. Additionally, the study examines windage heating due to shear work from rotating walls, including the seal teeth surface. The amount of shear work done on the leakage flow and the corresponding rise in fluid temperature were quantified, tabulated, and further compared with a simple analytical model, showing good agreement between them and, hence, validating the numerical approach used.

Canine morphometrics as a tool for distinguishing species, sex, and age class in Southern Ocean fur seals.

Carcasses resulting from natural mortalities are invaluable for use in scientific studies, provided species, sex, and age class are known. When such data are unavailable, identifying skeletal remains is necessary if one is to use the information contained within samples. Teeth are amongst the best preserved skeletal remains owing to the durability of enamel and dentine. Here, we tested whether external measurements of canines could be used to distinguish two partially sympatric species of Southern Ocean fur seals, the Antarctic Arctocephalus gazella and Sub-Antarctic A. tropicalis fur seals. We also investigated whether the external measurements of canines could be used to determine the age, sex, as well as island of origin of the animals. Eight morphological variables (crown length, root length, crown width, root width, crown thickness, root thickness, total canine length, and count of external surface annular ridges) were recorded from canines of 340 individuals of known species, sex, and island of origin. The count of external annular ridges provided a good estimate of age, which was confirmed by counting the growth layer groups of sectioned teeth, especially for older animals (> 9 years old). External canine measurements proved useful in distinguishing species, as well as sex within and between species, particularly in adult animals. Species were more difficult to distinguish in females than in males. The islands of origin could only be inferred in male Antarctic fur seals. This study indicates that fur seal teeth of unknown provenance, found either in breeding colonies or as vagrants, provide evidence on species, sex, and age of the animal, which increases the value of associated samples. It further highlights the importance of external measurements of skeletal remains such as canine teeth in separating closely related species.

CFD-Predicted Rotordynamic Characteristics for High-Temperature Water Liquid Seal Considering Tooth Deformation

With the development of high-temperature centrifugal pump, the temperature of the medium in the pump must be higher than the normal water temperature. It is particularly important to study the rotordynamic characteristics of the seal at high temperature due to it being the core component of the rotor system. This paper takes the high temperature water liquid seal as a research object to study its rotordynamic characteristics based on the fluid-solid-thermal coupling, the deformation of seal teeth under thermal and dynamic loads was calculated. Based on the test rig, the leakage flow rate and drag power loss of water liquid seal at 20 °C, 50 °C, and 86 °C temperatures were tested and compared with the CFD (Computational Fluid Dynamics) calculation. Meanwhile, the DEFINE-CG-MOTION and DEFINE-PROFILE control macro were used to establish the rotor whirling equation, the frequency-independent rotordynamic coefficients (K, k, C, c) and frequency-dependent rotordynamic coefficients (Keff,Ceff) were evaluated by transient CFD method. This analysis was done at three different pressure drops (2.08, 4.12, and 8.25 bar) and three rotational speeds (2000, 4000, and 6000 r/min). The results show that with the increase of water temperature, both the leakage flow rate and drag power loss decrease, indicating the 86 °C water seal has a better sealing capacity. From the rotordynamic perspective, with the increase of water temperature, the direct stiffness coefficient decreases, and the effective stiffness coefficient Keff for 20 °C water seal possesses a better stiffness capability than the other two temperature seals. The effective damping coefficient Ceff for 20 °C water seal is larger than the other two temperature seals, which means it is more stable for the rotor system.

Tortuous flow path design for leakage reduction of labyrinth seal

This study proposes a new seal design to reduce the leakage in turbomachines. On the basis of the conventional labyrinth seal, two vertical blocking walls are added on the rotor, and one horizontal blocking wall is added on the upstream seal tooth and downstream seal tooth. In the new seal, a tortuous flow path is generated, and many vortexes appear. The new seal increases the resistance to the leakage fluid and kinetic energy dissipation. After the comparison of the leakage between the specially designed new seal and conventional labyrinth seal, it can be found that the specially designed new seal yields a reduction in the leakage of 42.7~43.6%.

Effect of the hub cavity leakage on the aerodynamic performance and strength characteristics of the 150 kW SCO2 centrifugal compressor

The hub cavity leakage has large effect on the aerodynamic performance on the Supercritical carbon dioxide (SCO2) centrifugal compressor. In this paper, the aerodynamic performance and strength characteristics of the 150 kW SCO2 centrifugal compressor with the hub cavity were numerically investigated using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) and [Formula: see text] turbulence model. The high precision physical properties tables of SCO2 were used to calculate the SCO2 property parameters across the centrifugal compressor flow passages. The aerodynamic performance of the 150 kW SCO2 centrifugal compressor without and with the hub cavity and the labyrinth seal at different mass flow coefficients was compared. The equivalent (von-Mises) stress and the deformation on the SCO2 centrifugal impeller were obtained by the combination of the aerodynamic pressure and centrifugal force calculation. The results show that the isentropic efficiency of the SCO2 centrifugal compressor without and with the hub cavity and the labyrinth seal at the designed flow coefficient equal 73.2% and 72.1% respectively. The effects of the hub cavity leakage on the pressure ratio of the SCO2 centrifugal compressor are limited. The hub cavity leakage decreases with the flow coefficient increasing. The similar isentropic efficiency of the SCO2 centrifugal compressor without and with the hub cavity and the labyrinth seal at the largest flow coefficient is obtained. The axial thrust of the SCO2 centrifugal compressor with the hub cavity and the labyrinth seal ranges from 1000N to 2000N at different flow coefficients, as well as keeps the same direction. The maximum equivalent (von-Mises) stress of the impeller is 109.95 MPa and less than the allowable stress 137 MPa (using 304 steel as the impeller material). The maximum deformation of the seal teeth is less than 0.003 mm. This work provides the reference of the compressor design and safety operation for the SCO2 centrifugal compressor.

Multi-decadal environmental change in the Barents Sea recorded by seal teeth.

Multiple environmental forcings, such as warming and changes in ocean circulation and nutrient supply, are affecting the base of Arctic marine ecosystems, with cascading effects on the entire food web through bottom‐up control. Stable nitrogen isotopes (δ15N) can be used to detect and unravel the impact of these forcings on this unique ecosystem, if the many processes that affect the δ15N values are constrained. Combining unique 60‐year records from compound specific δ15N biomarkers on harp seal teeth alongside state‐of‐the‐art ocean modelling, we observed a significant decline in the δ15N values at the base of the Barents Sea food web from 1951 to 2012. This strong and persistent decadal trend emerges due to the combination of anthropogenic atmospheric nitrogen deposition in the Atlantic, increased northward transport of Atlantic water through Arctic gateways and local feedbacks from increasing Arctic primary production. Our results suggest that the Arctic ecosystem has been responding to anthropogenically induced local and remote drivers, linked to changing ocean biology, chemistry and physics, for at least 60 years. Accounting for these trends in δ15N values at the base of the food web is essential to accurately detect ecosystem restructuring in this rapidly changing environment.

Novel Method of the Seal Aerodynamic Design to Reduce Leakage by Matching the Seal Geometry to Flow Conditions

This paper presents a novel method of labyrinth seals design. This method is based on CFD calculations and consists in the analysis of the phenomenon of gas kinetic energy carry-over in the seal chambers between clearances. The design method is presented in two variants. The first variant is designed for seals for which it is impossible to change their external dimensions (length and height). The second variant enables designing the seal geometry without changing the seal length and with a slight change of the seal height. Apart from the optimal distribution of teeth, this variant provides for adjusting chambers geometry to flow conditions. As the result of using both variants such design of the seal geometry with respect to leakage is obtained which enables achieving kinetic energy dissipation as uniform as possible in each chamber of the seal. The method was developed based on numerical calculations and the analysis of the flow phenomena. Calculation examples included in this paper show that the obtained reduction of leakage for the first variant ranges from 3.4% to 15.5%, when compared with the initial geometry. The relation between the number of seal teeth and the leakage rate is also analyzed here. The second variant allows for reduction of leakage rate by 15.4%, when compared with the geometry with the same number of teeth. It is shown that the newly designed geometry reveals almost stable relative reduction of leakage rate irrespective of the pressure ratio upstream and downstream the seal. The efficiency of the used method is proved for various heights of the seal clearance.

Compound-specific isotope analyses of harp seal teeth: tools for trophic ecology reconstruction

As sentinels of ecosystem health, high trophic level predators integrate information through all levels of the food web. Their tissues can be used to investigate spatiotemporal variability in foraging behaviour, and with the appropriate analytical methods and tools, archived samples can be used to reconstruct past trophic interactions. Harp seal Pagophilus groenlandicus teeth collected in the 1990s from the Northwest Atlantic were analysed for bulk stable carbon and nitrogen isotopes (δ13Cbulk and δ15Nbulk), and compound-specific stable nitrogen isotopes of amino acids (δ15NAA) for the first time. We developed a fine-scale, annual growth layer group (GLG) dentine sub-sampling method corresponding to the second and third year of life. In accordance with previous diet studies, while there was individual variability in δ15Nbulk, δ13Cbulk and δ15NAA measurements, we did not detect significant differences in isotopic niche widths between males and females, or between GLGs. Relative trophic position was calculated as the baseline-corrected δ15NAA values using trophic (glutamic acid) and source (phenylalanine and glycine) amino acids. Variability was measured between individuals in their relative trophic position, but within-individual variability was low, suggesting that they fed at the same trophic level over these 2 yr of life. These novel δ15NAA data may therefore suggest individual, specialist harp seal foraging behaviour in sub-adults. Our findings show that compound-specific stable isotope signatures of archived, inert predator tissues can be used as tools for the retrospective reconstruction of trophic interactions on broad spatiotemporal scales.

Theoretical and experimental research towards labyrinth sealing mechanism of liquid nitrogen in the cryogenic spindle

Labyrinth seal works as an inter-stage seal in the cryogenic spindle which is provided with the through-tool cooling feature of liquid nitrogen. The thermoelastic deformation of seal teeth and cryogenic cavitation inevitably take place in labyrinth sealing for liquid nitrogen which really matters the cryogenic sealing. It is highly essential to discuss how these factors impact the sealing effectiveness at the theoretical level. This study aims to theoretically model the cryogenic labyrinth seal in the spindle. New leakage equations concerning both deformation and cavitation are presented for a quantitative calculation, in which their effects on sealing capacity are revealed. Confirmations of the calculation results with experimental data are performed to better recognize the phenomena arising in sealing process in the spindle. The results indicate that the equations heavily rely on seal structural parameters and fluid physical variables. The structural parameters can be altered by the deformation especially the increase of tooth clearance leads to a leakage rise. The physical variables are changed by the cavitation, particularly the formation of vapor phase decreases the leakage. However, the cavitation has a greater impact on the leakage than the deformation when below the critical supercooling. Low inlet pressure, low supercooling and seal material with low thermal expansion coefficient can promote the improvement of sealing capability. This work suggests series of relatively complete theoretical models for the cryogenic labyrinth seal.

Effect of Rotor-stator Axial Gap on the Tip Seal Leakage Flow of a Steam Turbine

The tip leakage flow in different axial gaps is numerically investigated based on the Reynolds-Averaged Navier-Stokes equations and k-ω SST turbulent model using commercial CFD software ANSYS Fluent. The characteristics of vortexes in the flow field of tip seal and the distribution law of rotor tip leakage loss are analyzed under the change of axial gap. The results show that the flow field in the blade tip seal undergoes complex changes with the increase of axial gap. There are two opposite vortices in the seal cavity with small axial gap, namely, the large vortex in the cavity and the small vortex near the wall of the shroud. The small vortex gradually disappears with the increase of the axial gap. When the axial gap is increased to a certain value, the reverse large vortex is formed in the cavity behind the low teeth of seal, and the leakage rate increases significantly; the steam flow angle and the mixing loss also show different changes. Based on the traditional calculation formula of tip leakage rate, a more accurate calculation formula of tip leakage rate is constructed by introducing equivalent labyrinth seal teeth to consider the variation of axial gap.

Numerical Analysis of Labyrinth Seal Performance for the Impeller Backface Cavity of a Supercritical CO2 Radial Inflow Turbine

For a radial inflow turbine (RIT), leakage flow in impeller backface cavity has critical impacts on aerodynamic performance of the RIT and axial force acting on the RIT impeller. In order to control this leakage flow, different types of labyrinth seals are numerically studied in this paper based on a supercritical carbon dioxide (S-CO2) RIT. The effects of seal clearance and cavity outlet pressure are first analyzed, and the impacts of seal design parameters, including height, number and shape of seal teeth, are evaluated. Results indicate that adding labyrinth seal can improve cavity pressure and hence adequately inhibits leakage flow. Decreasing the seal clearance and increasing the height of seal teeth are beneficial to improve sealing performance, and the same effect can be obtained by increasing the number of seal teeth. Meanwhile, employing seals can reduce leakage loss and improve RIT efficiency under a specific range of cavity outlet pressure. Finally, the influences of seal types on the flow field in seal cavity are numerically analyzed, and results demonstrate that isosceles trapezoidal type of seal cavity has better sealing performance than triangular, rectangular and right-angled trapezoidal seal cavities.

Experimental and Numerical Analysis of the Gas Flow in the Axisymmetric Radial Clearance

This paper focuses on the analysis of the gas flow in the axisymmetric mini gap bounded by the surface of the top of the labyrinth seal tooth and the surface of the body. It includes the results of experimental research and numerical calculations. Experimental research focused on the analysis of gas flow for six clearance heights in a wide range of pressure drops. Based on this research, we determined the mass flow in the clearance. Using the Saint-Venant equation, we determined the flow coefficient versus the pressure ratio upstream and downstream from the seal. Flow coefficients for various clearance heights obtained from the experiment can be divided into two data groups, the values of which differ significantly. To explain changes in the value of the gas flow coefficient for selected clearance heights, numerical analysis of the said gas flow was performed using the Fluent software. This analysis allowed us to explain the reason for the variability of the flow coefficient. This research can be the basis for determining the change of seal integrity during operation for staggered and stepped seals.

Numerical Investigation on Flow Characteristics and Aerodynamic Performance of a 1.5-Stage SCO2 Axial-Inflow Turbine with Labyrinth Seals

The leakage problem of supercritical carbon dioxide (SCO2) axial-inflow turbine brings great challenges to the efficiency and security of the power system. Labyrinth seals are usually utilized to improve the leakage characteristics of the blade tip. In this paper, a 1.5-stage SCO2 axial-inflow turbine is established and labyrinth seals are arranged on the top of the first stage stator and rotor blades. The effects of seal clearance, groove on seal cavity surface and circle groove shape on flow characteristics and aerodynamic performance under different pressure ratio are investigated. Increasing seal clearance can significantly weaken the turbine performance. Arranging rectangle, circle and V-shaped grooves on the seal cavity surface near the outlet of the seal gap can enhance the energy dissipation, reduce the relative leakage and improve the power and efficiency. Increasing the groove width can improve the aerodynamic performance while the effect of the groove depth is weak. The configuration where the circle groove width is 50% of the pitch of seal tooth achieves the best performance with the relative leakage of stator1 and rotor, power and efficiency of 6.04 × 10−3, 8.09 × 10−3, 3.467 MW and 86.86% respectively. With an increase in pressure ratio, the relative leakage increases firstly and then remains almost constant. The power increases while the efficiency increases firstly and then decreases, reaching the peak value under the design condition.

Study on the Rotordynamic Performance of a Novel Anti-stagnation Labyrinth Seal

A novel structure of anti-stagnation labyrinth seal was proposed in this paper. An opposed jet suppressing the circumferential flow was generated in seal cavities with pressure-driven micro-nozzles on adjacent seal teeth. The theoretical identification approach for rotordynamic coefficients based on the infinitesimal theory was applied to predict rotordynamic coefficients of annular gas seals. The effects of the layout of anti-stagnation nozzles, inlet pressure and rotational speed on rotordynamic characteristics were investigated using a computational fluid dynamics (CFD) method. Compared with that of the traditional labyrinth seal, the new seal possesses better stability with a 200% increase in the effective damping coefficients at high whirling frequency. Compared with those in the middle and downstream position, nozzles installed in the upstream of the seal can effectively improve the dynamic stability of the system. The anti-stagnation labyrinth seal shows better stability performance for higher inlet pressure and rotational speed. The leakage flow rate of the anti-stagnation labyrinth seal is slightly higher (an increase of less than 4%) than that of the original labyrinth seal.