Tooth bending damage resulting from an intense impact by the rotor sometimes occurs in the transient operation.To investigate the influence of after-damage clearance and tooth bending length on the leakage performance...Tooth bending damage resulting from an intense impact by the rotor sometimes occurs in the transient operation.To investigate the influence of after-damage clearance and tooth bending length on the leakage performance and rotordynamic coefficients of labyrinth seals,three tooth bending damages were taken into consideration,including the unbent tooth damage(abbreviated as Unbent),the partial tooth bending damage(abbreviated as Pbent)and the complete tooth bending damage(abbreviated as Cbent).The transient CFD solution was utilized to calculate the leakage flow rates and rotordynamic coefficients of labyrinth seals with clearances of 0.3,0.4,0.5,0.6 mm for three tooth bending damages.The obtained result shows that the Unbent tooth damage leaks least while the Pbent tooth bending damage leaks most,and an increase of 6.1%for Cbent tooth bending damage and an increase of 19.4%for Pbent tooth bending damage are discovered at the tooth clearance of 0.6 mm in comparison with the Unbent tooth damage.Compared to the Unbent tooth damage,the effective damping for Pbent tooth bending damage and Cbent tooth bending damage is lower and drops by 9.7%–33.6%and 8.5%–22.6%respectively at the tooth clearance of 0.6 mm,suggesting that Pbent tooth bending damage or Cbent tooth bending damage tends to weaken the seal stability when compared to the Unbent tooth damage.展开更多
Swirl brakes are usually introduced at the seal entrance in industry to improve the seal stability,especially for labyrinth seals suffering low seal clearance and high inlet preswirl ratio.However,how to arrange swirl...Swirl brakes are usually introduced at the seal entrance in industry to improve the seal stability,especially for labyrinth seals suffering low seal clearance and high inlet preswirl ratio.However,how to arrange swirl brakes at the seal entrance to obtain better seal stability retains unknown,such as the axial distance between the brake trailing edge and the first tooth.To this end,the effects of the distance between brakes and the first tooth on the leakage flow rate and seal rotordynamic coefficients were numerically investigated at typical inlet preswirl ratios of 0.45 and0.8,and the predicted results were in comparison with the results for no-brake configuration.The obtained results disclose that the brake configuration arranged against the first tooth produces lower circumferential velocity in the downstream of the brakes as a result of the larger counterclockwise vortex moving from the brake trailing edge to the brake leading edge when compared to the brake configuration away from the first tooth.Besides,the dropped circumferential velocity in the downstream of brakes will cause larger pressure fluctuation in the circumferential direction and thus generates larger tangential force to restrain the rotor forward whirl.On the other hand,the effective damping is further increased when the distance between brakes and the first tooth decreases to zero,that is,the crossover frequency is even disappeared at the inlet preswirl ratio of 0.45 and successfully drops from 69.9 Hz to 32.7 Hz at the preswirl ratio of 0.8.展开更多
The labyrinth seal in turbomachinery is a key element that restricts leakage flow among rotor-stator clearances from high-pressure regions to low-pressure regions. The fluid-induced forces on the rotor from seals duri...The labyrinth seal in turbomachinery is a key element that restricts leakage flow among rotor-stator clearances from high-pressure regions to low-pressure regions. The fluid-induced forces on the rotor from seals during machine operation must be accurately quantified to predict their dynamic behavior effectively. To understand the fluid-induced force characteristics of the labyrinth seal more fully, the effects of four types of pre-swirls on the leakage, flow field, and fluid-induced force of a rotary straight-through labyrinth gas seal (RSTLGS) were numerically investigated using the proposed steady computational fluid dynamics (CFD) method based on the three-dimensional models of the RSTLGS. The leakage, flow field, and fluid-induced force of the RSTLGS for six axial pre-swirl velocities, four radial preswirl angles, four circumferential positive pre-swirl angles, and four circumferential negative pre-swirl angles were computed under the same geometrical parameters and operational conditions. Mesh analysis ensures the accuracy of the present steady CFD method. The numerical results show that the four types of pre-swirls influence the leakage, flow field, and fluid-induced force of the RSTLGS. The axial pre-swirl velocity remarkably inhibits the fluid-induced force, and the circumferential positive pre-swirl angle and circumferential negative pre-swirl angle remarkably promote the fluid-induced force. The effects of the radial pre-swirl angle on the fluid-induced force are complicated, and the pressure forces and viscous forces show the maximum or minimum values at a specific radial pre-swirl angle. The pre-swirl has a negligible impact on the leakage. The four types of pre-swirls affect the leakage, flow field, and fluidinduced force of the RSTLGS to varying degrees. The pre-swirl is the influence factor affecting the leakage, flow field, and fluid-induced force of the RSTLGS. The conclusions will help to understand the fluid-induced force of labyrinth seals more fully, by providing helpful suggestions for engineering practices and a theoretical basis to analyze the fluid–structure interaction of the seal-rotor system in future research.展开更多
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,dif...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-CO_(2))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.展开更多
Recent studies on staggered labyrinth seals have focused on the effects of different parameters,such as the pressure ratio and rotational speed on the leakage flow rate.However,few investigations pay sufficient attent...Recent studies on staggered labyrinth seals have focused on the effects of different parameters,such as the pressure ratio and rotational speed on the leakage flow rate.However,few investigations pay sufficient attention to flow details and the sealing mechanism,which would be of practical importance in designing seals having higher performance.This paper establishes a theoretical model to study the seal mechanism,thus revealing that leakage is determined by the pressure ratio and geometric structure.Numerical simulation is implemented to illustrate details of the flow field within the seal structure.Viscous dissipation is used to quantitatively investigate the contribution that each location makes to the seal performance,revealing that orifices and stagnation points are the most important positions in the seal structure,generating the most dissipation.The orifice is carefully studied by using the theoretical model.Experiments for different pressure ratios are conducted and the results match well with those of the theoretical model and numerical simulation,verifying the theoretical model and analysis of the seal mechanism.Three new designs,based on a good understanding of the seal mechanism,are presented,with one reducing leakage by 24.5%.展开更多
Integrity of the membranous labyrinth barrier system is of critical importance, which promotes inner ear homeostasis and maintains its features. The membranous labyrinth barrier system is divided into several subsets ...Integrity of the membranous labyrinth barrier system is of critical importance, which promotes inner ear homeostasis and maintains its features. The membranous labyrinth barrier system is divided into several subsets of barriers which, although independent from each other, are interrelated. The same substance may demonstrate different permeability characteristics through different barriers and under different conditions, while different substances can have different permeability features even in the same barrier under the same condition. All parts of the mem-branous labyrinth barrier structure, including their morphology, enzymes and channel proteins, and theirs permeability characteristics under various physiological and pathological conditions are reviewed in this paper. Infections, noise exposure, ototoxicity may all increase perme-ability of the barriers and lead to disturbances in inner ear homeostasis. Copyright ? 2015 The Authors. Production & hosting by Elsevier (Singapore) Pte Ltd On behalf of PLA General Hospital Department of Otolaryngology Head and Neck Surgery. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).展开更多
Labyrinth seal can cause steam-exciting, the structural and operating parameters of labyrinth seal have effect on stability of rotor-system. For investigating the coupling influences of the structure and operating par...Labyrinth seal can cause steam-exciting, the structural and operating parameters of labyrinth seal have effect on stability of rotor-system. For investigating the coupling influences of the structure and operating parameters of labyrinth seals on dynamic coefficients, a model of calculating dynamic coefficients of labyrinth seals is presented using a two control volume model. The coupling influences of parameters on cross-coupled stiffness and direct damping of labyrinth seal are discussed. In the conclusion, a reference of preventing steam-exciting vibration and optimum determination of design parameters of labyrinth seals are provided.展开更多
The effects of the rotational speed on the fluid-induced force characteristics of a straight-through labyrinth gas seal( STLGS) are numerically investigated using the steady computational fluid dynamics( CFD) method b...The effects of the rotational speed on the fluid-induced force characteristics of a straight-through labyrinth gas seal( STLGS) are numerically investigated using the steady computational fluid dynamics( CFD) method based on a three-dimensional model of the STLGS. The fluid-induced force characteristics of the STLGS for five rotational speeds at a pressure drop of △P = 5000 Pa with and without eccentricity are computed. The grid density analysis ensures the accuracy of the present steady-CFD method. The effect and sensitivity analysis show that the changes in rotational speed affect the pressure forces,viscous forces and total pressure distributions on the rotor surface,velocity streamlines,leakage flow rates,and maximum flow velocities. The results indicate that the rotational speed inhibits the pressure forces,leakage flow rates and maximum flow velocities and promotes the viscous forces and total pressure on the rotor surface.展开更多
The influence of labyrinth seal structure parameters and their interaction on the characteristics of leakage amount are numerically investigated by conducting a quadratic regression orthogonal experiment. To determine...The influence of labyrinth seal structure parameters and their interaction on the characteristics of leakage amount are numerically investigated by conducting a quadratic regression orthogonal experiment. To determine the optimal structure parameters of the steam seal for minimizing the leakage amount, a reliable regression equation that does not lack of fit is established. The flow characteristics of the fluid in the labyrinth seal are analyzed in detail. Results show that the leakage amount is greatly influenced by seal cavity depth, convex platform height, seal tooth thickness, and tooth tip clearance, with the tip clearance having the most significant effect. The interaction among the four items exerts a certain impact on the leakage amount. The proposed regression equation exhibits a good significance and does not lack of fit. After optimization, the labyrinth seal demonstrates increased entropy and energy dissipation at the tip of the seal tooth, as well as decreased speed and inertia effect in the cavity, suggesting that the resistance leakage performance of the optimized labyrinth seal is improved.展开更多
Polysulfide absorption in a micropore-rich structure has been reported to be capable of efficiently confining the shuttle effect for high-performance lithium-sulfur(Li–S)batteries.Here,a labyrinth maze-like spherical...Polysulfide absorption in a micropore-rich structure has been reported to be capable of efficiently confining the shuttle effect for high-performance lithium-sulfur(Li–S)batteries.Here,a labyrinth maze-like spherical honeycomb-like carbon with micropore-rich structure was synthesized,which is employed as a template host material of sulfur to study the shuttle effects.The results strongly confirm that a diffusion controlled process rather than an absorption resulted surface-controlled process occurs in an even micropore-rich cathode but still greatly inhibits the shuttle effect.Thus,the battery achieves a high initial discharge specific capacity of 1120 mAh g1 at 0.25 C and super cycling stability for 1635 cycles with only 0.035%capacity decay per cycle with 100%Coulombic efficiency.We would like to propose a new mechanism for shuttle effect inhibition in micropores.In terms of the diffusion control process in microporous paths of a labyrinth maze structure,polysulfides experience a long travel to realize continuous reductions of sulfur and polysulfides until formation of the final solid product.This efficiently prevents the polysulfides escaping to electrolyte.The labyrinth maze-like honeycomb structure also offers fast electron transfer and enhanced mass transport as well as robust mechanical strength retaining intact structure for long cycle life.This work sheds lights on new fundamental insights behind the shuttle effects with universal significance while demonstrating prominent merits of a robust labyrinth maze-like structure in high performance cathode for high-performance Li–S batteries.展开更多
An accurate seal forces model is the foundation to analyze the rotor-seal systems. In this paper, the Navier-Stokes equation and energy equation are solved to simulate the interior flow field in the labyrinth seal gap...An accurate seal forces model is the foundation to analyze the rotor-seal systems. In this paper, the Navier-Stokes equation and energy equation are solved to simulate the interior flow field in the labyrinth seal gap. The leakage rate is compared with the experimental results in the literatures. The ：4maximum error is 4% , which proves that the method of employing CFD to simulate the interior flow field of labyrinth seal gap is reliable. Based on this, the interior flow field and fluid exciting force of stage teeth labyrinth seal are studied. By coupling with the Muszynska model, the method of defining the experience loss parameters in Muszynska model is proposed. The results indicate that the experience parameters obtained by the proposed method can depict the nonlinear exciting force of labyrinth seal better.展开更多
Multiple analytical methods and Monte Carlo simulations were performed to evaluate neutron penetration in straight and curved labyrinths. Factors studied included variations in beam losses of off-axis point source,on-...Multiple analytical methods and Monte Carlo simulations were performed to evaluate neutron penetration in straight and curved labyrinths. Factors studied included variations in beam losses of off-axis point source,on-axis point source,and line source. For the straight labyrinth, it was found that the analytical expressions neglect the dose rate platform appearing at the bend of the labyrinth, and the agreement between analytical methods and Monte Carlo estimation was related to the type of neutron source term. For the curved labyrinth, the neutron attenuation length obtained under different conditions was nearly identical and appeared to be in quite good accord with the empirical formula calculation. Moreover, the neutron energy spectra along the centerline distance of the labyrinth were also analyzed. In the first leg, differences in beam loss led to variance in the distribution of spectra,while in the second and subsequent legs, the spectra were similar, where the main contributors were thermal neutrons. This work is valuable for practical design of the labyrinths in the accelerator facilities.展开更多
One of the important problems to be tackled in turbo machines is the leakage dynamics characteristics of labyrinth seals. In this paper we analyzed the effect of labyrinth seal structure and the change in fluid flow p...One of the important problems to be tackled in turbo machines is the leakage dynamics characteristics of labyrinth seals. In this paper we analyzed the effect of labyrinth seal structure and the change in fluid flow pressure on the leakage characteristics of seal. Computational fluid dynamics (CFD) model for 3D labyrinth seal was built which provides a basis for reducing steam flow excitation. The streamline pattern and the pressure drop characteristics for leakage of steam through a labyrinth seal was investigated. Simulations of internal flow and leakage characteristics had been performed by CFD software and Black-Child model. The results showed that the amount of leakage is directly proportional to the tooth gap and inlet pressure and inversely proportional to the cavity depth and outlet pressure. The proposed CFD model provides a feasible method to predict the leakage characteristics of labyrinth seal in response to the structure of seal and the change in inlet-outlet pressures.展开更多
Northern labyrinths are stone constructions of different shapes, dating back to III-I century BC. They mainly appear on capes on peninsulas and islands up to 13-25 metresabove the sea level. Their area begins from Sci...Northern labyrinths are stone constructions of different shapes, dating back to III-I century BC. They mainly appear on capes on peninsulas and islands up to 13-25 metresabove the sea level. Their area begins from Scilly Isles (England) and in the White Sea (Russia). Opinions of scientists concerning their designation are controversial. Assumptions about their practical meaning haven’t been proved: no burials have been found underneath;fishing equipment cannot be located so far from the area of tides. Most of the scientists link labyrinths with the sphere of spiritual culture: sanctuaries, altars, sacred places, schemes of rituals and magical centers. Assumptions about calendar designation link the picture of labyrinth with schemes of orbits of the Sun, the Moon, planets and stars. However they do not explain the application of this technology. The author’s concept is based on the opposite astronomical alignment by the shade of gnomon and considers peculiarities of the geographical space of Northern regions (polar days and white nights). The aim of the research is to prove that the key to decoding the picture of a classic Northern labyrinth is a gnomon located in the centre of the construction. Field research has been conducted on Zayztskiy Island in Solovetskiy Archipelago. Experiments of imitation modeling have been done, analysis of linguistic and toponymic materials, archeological, astronomical, ethnographical and mythological and other sources has been implemented. The research has proved that observations of the shade can help to create a calendar in a shape of a bispiral labyrinth. The structure of labyrinth is convenient for defining the North, dividing daytime and defining geographical altitude of the observation point. Orientation in space and time has become the basis for navigation frame of the territory. A set of stone instruments is the key of a navigation frame of the territory. Life-essential stages of the yearly lighting are reflected in specific geometry shapes of shades. They have been preserved in mythological images of the Sun, solar symbols and modern sign systems. Languages, alphabets, numeric systems can be considered as models of geographical space and have evolved thanks to observations of the light movement. Key results of the research: 1) in the past the Sun used to play the leading role in navigation in the North because reference points of the dark sky were not available for observation;2) Northern labyrinths have been created and used thanks to gnomon;3) gnomon has been in the sphere of sacred knowledge for a long time, it was integrated as sundial 2.5 thousand years ago;4) most symbols of the Sun and the Time are connected with gnomon and labyrinth;5) the Sun, observation tools and results of observations are reflected in models of the world around—navigation, linguistic, toponymical, mythological, sacral and semiotic;6) The universal sense of Time helps to understand a wide range of meanings of a sign of a labyrinth: birth;life stages (status, transitions initiations);space time order;reproduction of the benefits, fertility, abundance;knowledge and forecast;management: law and order;eternity-revival;7) Use of solar navigation in formation of information systems is based on steady ratios “natural process—a geometrical sign (the sum of shadows in one day or year)”, universal opportunities of existential parameters for designation of objects, general availability and vital need of this knowledge.展开更多
Umbrella-type mud-water diversion labyrinth sedimentation device,which is characterized by the combination of two swash plate and wing plate into an umbrella type with a set angle,the angle range of the two swash plat...Umbrella-type mud-water diversion labyrinth sedimentation device,which is characterized by the combination of two swash plate and wing plate into an umbrella type with a set angle,the angle range of the two swash plate is 15º--100º,the vertical height of the swash plate is 60-70 mm,the parallel axis of the wing plate is the vertical direction,the height is 10-20 mm.the whole adopts the modular combination mode,and can be freely combined and disassembled according to different pond design,swash plate The interval(sedimentation distance)can be freely adjusted,mud take the mud road and water take the water road,to avoid the mutual interference of the water and mud road,to achieve the stability of the water quality.The turbidity of the sedimentation pond is low,stable in 0.3-2.0 NTU.展开更多
Labyrinth weirs provide higher discharge capacity than conventional weirs, with the ability to pass large flows at comparatively low heads. Labyrinth weirs are primarily used as spillways for dams where the spillway w...Labyrinth weirs provide higher discharge capacity than conventional weirs, with the ability to pass large flows at comparatively low heads. Labyrinth weirs are primarily used as spillways for dams where the spillway width is restricted. In recent years, many research investigations have considered the hydraulic performance of labyrinth weirs, particularly as dependent on the geometric features. The previous work has improved the design basis for such weirs. However, their design still requires experimentally derived and generalized performance curves. It is especially important to observe the behavior of the weir nappe to ensure the design provides hydraulic optimization and to account for pressure fluctuations, possible vibrations, resonance effect, noise and flow surging. In the present study, discharge coefficients were experimentally determined for both circular labyrinth weirs and sharp crested trapezoidal labyrinth weirs of varying side wall angle (α). Additional studies were completed with nappe breakers included to reduce the impact of vibration on the labyrinth weirs. In general, the test data indicated that nappe breakers placed on the trapezoidal labyrinth weirs and circular labyrinth weirs reduced the discharge coefficient by up to 4% of the un-amended weir.展开更多
The labyrinth weir is a non-gate controlled discharge structure which has a broken-line overflow weir on surface to get longer length of overflow frontier,and has advantages of simple structure,larger discharge and co...The labyrinth weir is a non-gate controlled discharge structure which has a broken-line overflow weir on surface to get longer length of overflow frontier,and has advantages of simple structure,larger discharge and convenient operation,and so on.It's mainly used in spillway of medium and small reservoirs with advantage of improving the discharge capacity for both newly built spillway and reconstruction one.Based on the design of Anzihe reservoir,the paper preliminary explores the water flow regime,discharge capacity and hydraulic design of the labyrinth weir.The result of calculation and test is the discharge capacity of labyrinth is greater than the broad crest weir and practical weir under the same water head and more superiority under the lower water head.展开更多
Based on the thermodynamically modified Zwart cavitation model,a two-dimensional theoretical cavitation flow model of the labyrinth seal between the piston and cylinder in a liquid hydrogen piston pump is established ...Based on the thermodynamically modified Zwart cavitation model,a two-dimensional theoretical cavitation flow model of the labyrinth seal between the piston and cylinder in a liquid hydrogen piston pump is established and verified.The influence of cavitation on the pressure distribution along the clearance seal,which reduces the leakage rate,is analyzed.The influence of input pressure and degree of subcooling on the cavitation flow is discussed.Higher inlet pressure and degree of subcooling can diminish the sealing effect between cavitation and liquid-phase flows.Furthermore,the leakage rates for clearance and labyrinth seals with 20-to 60-μm sealing gap are compared.When the sealing gap is no less than 30μm,the labyrinth sealing effect is superior to clearance seal.Finally,the leakage rates of labyrinth seals with three cavity structures—square,curve,and triangle—are simulated.The sealing effects are ordered as follows:square labyrinth cavity,curved labyrinth cavity,and triangular labyrinth cavity.The sealing effect is preferred when the optimal length-to-width ratio of the square cavity is around 5.0.The studies are further helpful to decrease the leakage rate of labyrinth seals and enhance volumetric efficiency in liquid hydrogen piston pump.展开更多
基金funded by the National Key R&D Program of China(No.2017YFB0601804)the National Natural Science Foundation of China(No.51776152)。
文摘Tooth bending damage resulting from an intense impact by the rotor sometimes occurs in the transient operation.To investigate the influence of after-damage clearance and tooth bending length on the leakage performance and rotordynamic coefficients of labyrinth seals,three tooth bending damages were taken into consideration,including the unbent tooth damage(abbreviated as Unbent),the partial tooth bending damage(abbreviated as Pbent)and the complete tooth bending damage(abbreviated as Cbent).The transient CFD solution was utilized to calculate the leakage flow rates and rotordynamic coefficients of labyrinth seals with clearances of 0.3,0.4,0.5,0.6 mm for three tooth bending damages.The obtained result shows that the Unbent tooth damage leaks least while the Pbent tooth bending damage leaks most,and an increase of 6.1%for Cbent tooth bending damage and an increase of 19.4%for Pbent tooth bending damage are discovered at the tooth clearance of 0.6 mm in comparison with the Unbent tooth damage.Compared to the Unbent tooth damage,the effective damping for Pbent tooth bending damage and Cbent tooth bending damage is lower and drops by 9.7%–33.6%and 8.5%–22.6%respectively at the tooth clearance of 0.6 mm,suggesting that Pbent tooth bending damage or Cbent tooth bending damage tends to weaken the seal stability when compared to the Unbent tooth damage.
基金funded by the National Key R&D Program of China(No.2017YFB0601804)the National Natural Science Foundation of China(No.51776152)。
文摘Swirl brakes are usually introduced at the seal entrance in industry to improve the seal stability,especially for labyrinth seals suffering low seal clearance and high inlet preswirl ratio.However,how to arrange swirl brakes at the seal entrance to obtain better seal stability retains unknown,such as the axial distance between the brake trailing edge and the first tooth.To this end,the effects of the distance between brakes and the first tooth on the leakage flow rate and seal rotordynamic coefficients were numerically investigated at typical inlet preswirl ratios of 0.45 and0.8,and the predicted results were in comparison with the results for no-brake configuration.The obtained results disclose that the brake configuration arranged against the first tooth produces lower circumferential velocity in the downstream of the brakes as a result of the larger counterclockwise vortex moving from the brake trailing edge to the brake leading edge when compared to the brake configuration away from the first tooth.Besides,the dropped circumferential velocity in the downstream of brakes will cause larger pressure fluctuation in the circumferential direction and thus generates larger tangential force to restrain the rotor forward whirl.On the other hand,the effective damping is further increased when the distance between brakes and the first tooth decreases to zero,that is,the crossover frequency is even disappeared at the inlet preswirl ratio of 0.45 and successfully drops from 69.9 Hz to 32.7 Hz at the preswirl ratio of 0.8.
基金Supported by National Basic Research Program of China(973 Program,Grant No.2012CB026006)
文摘The labyrinth seal in turbomachinery is a key element that restricts leakage flow among rotor-stator clearances from high-pressure regions to low-pressure regions. The fluid-induced forces on the rotor from seals during machine operation must be accurately quantified to predict their dynamic behavior effectively. To understand the fluid-induced force characteristics of the labyrinth seal more fully, the effects of four types of pre-swirls on the leakage, flow field, and fluid-induced force of a rotary straight-through labyrinth gas seal (RSTLGS) were numerically investigated using the proposed steady computational fluid dynamics (CFD) method based on the three-dimensional models of the RSTLGS. The leakage, flow field, and fluid-induced force of the RSTLGS for six axial pre-swirl velocities, four radial preswirl angles, four circumferential positive pre-swirl angles, and four circumferential negative pre-swirl angles were computed under the same geometrical parameters and operational conditions. Mesh analysis ensures the accuracy of the present steady CFD method. The numerical results show that the four types of pre-swirls influence the leakage, flow field, and fluid-induced force of the RSTLGS. The axial pre-swirl velocity remarkably inhibits the fluid-induced force, and the circumferential positive pre-swirl angle and circumferential negative pre-swirl angle remarkably promote the fluid-induced force. The effects of the radial pre-swirl angle on the fluid-induced force are complicated, and the pressure forces and viscous forces show the maximum or minimum values at a specific radial pre-swirl angle. The pre-swirl has a negligible impact on the leakage. The four types of pre-swirls affect the leakage, flow field, and fluidinduced force of the RSTLGS to varying degrees. The pre-swirl is the influence factor affecting the leakage, flow field, and fluid-induced force of the RSTLGS. The conclusions will help to understand the fluid-induced force of labyrinth seals more fully, by providing helpful suggestions for engineering practices and a theoretical basis to analyze the fluid–structure interaction of the seal-rotor system in future research.
基金founded by the National Key R&D Program of China(Contract No.2016YFB060010)National Natural Science Foundation of China(Grant Nos.51606026 and 51876021)the Fundamental Research Funds for the Central Universities.
文摘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-CO_(2))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.
基金Supported by National Natural Science Foundation of China(Grant No.51136003)the support provided by Doctor HUANG Weifeng,Doctor LI Yongjian,and Professor WANG Yuming at Department,of Mechanical Engineering, Tsinghua University,China,in establishing the test rig for the labyrinth seal
文摘Recent studies on staggered labyrinth seals have focused on the effects of different parameters,such as the pressure ratio and rotational speed on the leakage flow rate.However,few investigations pay sufficient attention to flow details and the sealing mechanism,which would be of practical importance in designing seals having higher performance.This paper establishes a theoretical model to study the seal mechanism,thus revealing that leakage is determined by the pressure ratio and geometric structure.Numerical simulation is implemented to illustrate details of the flow field within the seal structure.Viscous dissipation is used to quantitatively investigate the contribution that each location makes to the seal performance,revealing that orifices and stagnation points are the most important positions in the seal structure,generating the most dissipation.The orifice is carefully studied by using the theoretical model.Experiments for different pressure ratios are conducted and the results match well with those of the theoretical model and numerical simulation,verifying the theoretical model and analysis of the seal mechanism.Three new designs,based on a good understanding of the seal mechanism,are presented,with one reducing leakage by 24.5%.
文摘Integrity of the membranous labyrinth barrier system is of critical importance, which promotes inner ear homeostasis and maintains its features. The membranous labyrinth barrier system is divided into several subsets of barriers which, although independent from each other, are interrelated. The same substance may demonstrate different permeability characteristics through different barriers and under different conditions, while different substances can have different permeability features even in the same barrier under the same condition. All parts of the mem-branous labyrinth barrier structure, including their morphology, enzymes and channel proteins, and theirs permeability characteristics under various physiological and pathological conditions are reviewed in this paper. Infections, noise exposure, ototoxicity may all increase perme-ability of the barriers and lead to disturbances in inner ear homeostasis. Copyright ? 2015 The Authors. Production & hosting by Elsevier (Singapore) Pte Ltd On behalf of PLA General Hospital Department of Otolaryngology Head and Neck Surgery. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
基金This project is supported by National Natural Science Foundation of China(59990472). Manuscript received on November 30, 1999 r
文摘Labyrinth seal can cause steam-exciting, the structural and operating parameters of labyrinth seal have effect on stability of rotor-system. For investigating the coupling influences of the structure and operating parameters of labyrinth seals on dynamic coefficients, a model of calculating dynamic coefficients of labyrinth seals is presented using a two control volume model. The coupling influences of parameters on cross-coupled stiffness and direct damping of labyrinth seal are discussed. In the conclusion, a reference of preventing steam-exciting vibration and optimum determination of design parameters of labyrinth seals are provided.
基金Supported by the National Basic Research Development Program of China(No.2012CB026006)
文摘The effects of the rotational speed on the fluid-induced force characteristics of a straight-through labyrinth gas seal( STLGS) are numerically investigated using the steady computational fluid dynamics( CFD) method based on a three-dimensional model of the STLGS. The fluid-induced force characteristics of the STLGS for five rotational speeds at a pressure drop of △P = 5000 Pa with and without eccentricity are computed. The grid density analysis ensures the accuracy of the present steady-CFD method. The effect and sensitivity analysis show that the changes in rotational speed affect the pressure forces,viscous forces and total pressure distributions on the rotor surface,velocity streamlines,leakage flow rates,and maximum flow velocities. The results indicate that the rotational speed inhibits the pressure forces,leakage flow rates and maximum flow velocities and promotes the viscous forces and total pressure on the rotor surface.
文摘The influence of labyrinth seal structure parameters and their interaction on the characteristics of leakage amount are numerically investigated by conducting a quadratic regression orthogonal experiment. To determine the optimal structure parameters of the steam seal for minimizing the leakage amount, a reliable regression equation that does not lack of fit is established. The flow characteristics of the fluid in the labyrinth seal are analyzed in detail. Results show that the leakage amount is greatly influenced by seal cavity depth, convex platform height, seal tooth thickness, and tooth tip clearance, with the tip clearance having the most significant effect. The interaction among the four items exerts a certain impact on the leakage amount. The proposed regression equation exhibits a good significance and does not lack of fit. After optimization, the labyrinth seal demonstrates increased entropy and energy dissipation at the tip of the seal tooth, as well as decreased speed and inertia effect in the cavity, suggesting that the resistance leakage performance of the optimized labyrinth seal is improved.
基金Supplementary data to this article can be found online at https://doi.org/10.1016/j.matre.2022.100159.
文摘Polysulfide absorption in a micropore-rich structure has been reported to be capable of efficiently confining the shuttle effect for high-performance lithium-sulfur(Li–S)batteries.Here,a labyrinth maze-like spherical honeycomb-like carbon with micropore-rich structure was synthesized,which is employed as a template host material of sulfur to study the shuttle effects.The results strongly confirm that a diffusion controlled process rather than an absorption resulted surface-controlled process occurs in an even micropore-rich cathode but still greatly inhibits the shuttle effect.Thus,the battery achieves a high initial discharge specific capacity of 1120 mAh g1 at 0.25 C and super cycling stability for 1635 cycles with only 0.035%capacity decay per cycle with 100%Coulombic efficiency.We would like to propose a new mechanism for shuttle effect inhibition in micropores.In terms of the diffusion control process in microporous paths of a labyrinth maze structure,polysulfides experience a long travel to realize continuous reductions of sulfur and polysulfides until formation of the final solid product.This efficiently prevents the polysulfides escaping to electrolyte.The labyrinth maze-like honeycomb structure also offers fast electron transfer and enhanced mass transport as well as robust mechanical strength retaining intact structure for long cycle life.This work sheds lights on new fundamental insights behind the shuttle effects with universal significance while demonstrating prominent merits of a robust labyrinth maze-like structure in high performance cathode for high-performance Li–S batteries.
基金the National Natural Science Foundation of China (Grant No. 10632040)
文摘An accurate seal forces model is the foundation to analyze the rotor-seal systems. In this paper, the Navier-Stokes equation and energy equation are solved to simulate the interior flow field in the labyrinth seal gap. The leakage rate is compared with the experimental results in the literatures. The ：4maximum error is 4% , which proves that the method of employing CFD to simulate the interior flow field of labyrinth seal gap is reliable. Based on this, the interior flow field and fluid exciting force of stage teeth labyrinth seal are studied. By coupling with the Muszynska model, the method of defining the experience loss parameters in Muszynska model is proposed. The results indicate that the experience parameters obtained by the proposed method can depict the nonlinear exciting force of labyrinth seal better.
基金supported by the National Key R&D Program of China(No.2017YFC0107700)
文摘Multiple analytical methods and Monte Carlo simulations were performed to evaluate neutron penetration in straight and curved labyrinths. Factors studied included variations in beam losses of off-axis point source,on-axis point source,and line source. For the straight labyrinth, it was found that the analytical expressions neglect the dose rate platform appearing at the bend of the labyrinth, and the agreement between analytical methods and Monte Carlo estimation was related to the type of neutron source term. For the curved labyrinth, the neutron attenuation length obtained under different conditions was nearly identical and appeared to be in quite good accord with the empirical formula calculation. Moreover, the neutron energy spectra along the centerline distance of the labyrinth were also analyzed. In the first leg, differences in beam loss led to variance in the distribution of spectra,while in the second and subsequent legs, the spectra were similar, where the main contributors were thermal neutrons. This work is valuable for practical design of the labyrinths in the accelerator facilities.
基金Sponsored by the National Natural Science Foundation of China (Grant No.10872054,10872055 and 50903082)
文摘One of the important problems to be tackled in turbo machines is the leakage dynamics characteristics of labyrinth seals. In this paper we analyzed the effect of labyrinth seal structure and the change in fluid flow pressure on the leakage characteristics of seal. Computational fluid dynamics (CFD) model for 3D labyrinth seal was built which provides a basis for reducing steam flow excitation. The streamline pattern and the pressure drop characteristics for leakage of steam through a labyrinth seal was investigated. Simulations of internal flow and leakage characteristics had been performed by CFD software and Black-Child model. The results showed that the amount of leakage is directly proportional to the tooth gap and inlet pressure and inversely proportional to the cavity depth and outlet pressure. The proposed CFD model provides a feasible method to predict the leakage characteristics of labyrinth seal in response to the structure of seal and the change in inlet-outlet pressures.
文摘Northern labyrinths are stone constructions of different shapes, dating back to III-I century BC. They mainly appear on capes on peninsulas and islands up to 13-25 metresabove the sea level. Their area begins from Scilly Isles (England) and in the White Sea (Russia). Opinions of scientists concerning their designation are controversial. Assumptions about their practical meaning haven’t been proved: no burials have been found underneath;fishing equipment cannot be located so far from the area of tides. Most of the scientists link labyrinths with the sphere of spiritual culture: sanctuaries, altars, sacred places, schemes of rituals and magical centers. Assumptions about calendar designation link the picture of labyrinth with schemes of orbits of the Sun, the Moon, planets and stars. However they do not explain the application of this technology. The author’s concept is based on the opposite astronomical alignment by the shade of gnomon and considers peculiarities of the geographical space of Northern regions (polar days and white nights). The aim of the research is to prove that the key to decoding the picture of a classic Northern labyrinth is a gnomon located in the centre of the construction. Field research has been conducted on Zayztskiy Island in Solovetskiy Archipelago. Experiments of imitation modeling have been done, analysis of linguistic and toponymic materials, archeological, astronomical, ethnographical and mythological and other sources has been implemented. The research has proved that observations of the shade can help to create a calendar in a shape of a bispiral labyrinth. The structure of labyrinth is convenient for defining the North, dividing daytime and defining geographical altitude of the observation point. Orientation in space and time has become the basis for navigation frame of the territory. A set of stone instruments is the key of a navigation frame of the territory. Life-essential stages of the yearly lighting are reflected in specific geometry shapes of shades. They have been preserved in mythological images of the Sun, solar symbols and modern sign systems. Languages, alphabets, numeric systems can be considered as models of geographical space and have evolved thanks to observations of the light movement. Key results of the research: 1) in the past the Sun used to play the leading role in navigation in the North because reference points of the dark sky were not available for observation;2) Northern labyrinths have been created and used thanks to gnomon;3) gnomon has been in the sphere of sacred knowledge for a long time, it was integrated as sundial 2.5 thousand years ago;4) most symbols of the Sun and the Time are connected with gnomon and labyrinth;5) the Sun, observation tools and results of observations are reflected in models of the world around—navigation, linguistic, toponymical, mythological, sacral and semiotic;6) The universal sense of Time helps to understand a wide range of meanings of a sign of a labyrinth: birth;life stages (status, transitions initiations);space time order;reproduction of the benefits, fertility, abundance;knowledge and forecast;management: law and order;eternity-revival;7) Use of solar navigation in formation of information systems is based on steady ratios “natural process—a geometrical sign (the sum of shadows in one day or year)”, universal opportunities of existential parameters for designation of objects, general availability and vital need of this knowledge.
文摘Umbrella-type mud-water diversion labyrinth sedimentation device,which is characterized by the combination of two swash plate and wing plate into an umbrella type with a set angle,the angle range of the two swash plate is 15º--100º,the vertical height of the swash plate is 60-70 mm,the parallel axis of the wing plate is the vertical direction,the height is 10-20 mm.the whole adopts the modular combination mode,and can be freely combined and disassembled according to different pond design,swash plate The interval(sedimentation distance)can be freely adjusted,mud take the mud road and water take the water road,to avoid the mutual interference of the water and mud road,to achieve the stability of the water quality.The turbidity of the sedimentation pond is low,stable in 0.3-2.0 NTU.
文摘Labyrinth weirs provide higher discharge capacity than conventional weirs, with the ability to pass large flows at comparatively low heads. Labyrinth weirs are primarily used as spillways for dams where the spillway width is restricted. In recent years, many research investigations have considered the hydraulic performance of labyrinth weirs, particularly as dependent on the geometric features. The previous work has improved the design basis for such weirs. However, their design still requires experimentally derived and generalized performance curves. It is especially important to observe the behavior of the weir nappe to ensure the design provides hydraulic optimization and to account for pressure fluctuations, possible vibrations, resonance effect, noise and flow surging. In the present study, discharge coefficients were experimentally determined for both circular labyrinth weirs and sharp crested trapezoidal labyrinth weirs of varying side wall angle (α). Additional studies were completed with nappe breakers included to reduce the impact of vibration on the labyrinth weirs. In general, the test data indicated that nappe breakers placed on the trapezoidal labyrinth weirs and circular labyrinth weirs reduced the discharge coefficient by up to 4% of the un-amended weir.
文摘The labyrinth weir is a non-gate controlled discharge structure which has a broken-line overflow weir on surface to get longer length of overflow frontier,and has advantages of simple structure,larger discharge and convenient operation,and so on.It's mainly used in spillway of medium and small reservoirs with advantage of improving the discharge capacity for both newly built spillway and reconstruction one.Based on the design of Anzihe reservoir,the paper preliminary explores the water flow regime,discharge capacity and hydraulic design of the labyrinth weir.The result of calculation and test is the discharge capacity of labyrinth is greater than the broad crest weir and practical weir under the same water head and more superiority under the lower water head.
基金supported by the National Key Research and Development Program of Ministry of Science and Technology(grant numbers:2020YFB1506201 and 2020YFB1506200).
文摘Based on the thermodynamically modified Zwart cavitation model,a two-dimensional theoretical cavitation flow model of the labyrinth seal between the piston and cylinder in a liquid hydrogen piston pump is established and verified.The influence of cavitation on the pressure distribution along the clearance seal,which reduces the leakage rate,is analyzed.The influence of input pressure and degree of subcooling on the cavitation flow is discussed.Higher inlet pressure and degree of subcooling can diminish the sealing effect between cavitation and liquid-phase flows.Furthermore,the leakage rates for clearance and labyrinth seals with 20-to 60-μm sealing gap are compared.When the sealing gap is no less than 30μm,the labyrinth sealing effect is superior to clearance seal.Finally,the leakage rates of labyrinth seals with three cavity structures—square,curve,and triangle—are simulated.The sealing effects are ordered as follows:square labyrinth cavity,curved labyrinth cavity,and triangular labyrinth cavity.The sealing effect is preferred when the optimal length-to-width ratio of the square cavity is around 5.0.The studies are further helpful to decrease the leakage rate of labyrinth seals and enhance volumetric efficiency in liquid hydrogen piston pump.
