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
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
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
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
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
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
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
Experimental investigation of stepped and straight-through labyrinth seals was designed to study the sealing performance of two different typical labyrinth seals.In order to facilitate dimensional analysis on the flow...Experimental investigation of stepped and straight-through labyrinth seals was designed to study the sealing performance of two different typical labyrinth seals.In order to facilitate dimensional analysis on the flow resistance characteristics of labyrinth seals,the variable cross-section of the flow channels are considered as constant cross-section flow.The mechanical energy loss of flow caused by throttle turbulence intensity is considered as caused by friction along the way.The friction coefficient of stepped labyrinth seals is bigger than that of straight-through labyrinth seals by more than 40% for the same Reynolds number and the ratio of equivalent diameter and the seal length.The expression of friction coefficient /and /Re are obtained from experimental data.The verifications indicate that the expressions are highly accurate.The contribution to the total pressure drop of each tooth cavity gradually becomes less along the flow direction.展开更多
The leakage flow through two labyrinth seals, e.g the interlocking seal and the stepped seal, was numerically investigated. Preliminary calculation of the seal-cavity averaged pressure by using the one-dimensional con...The leakage flow through two labyrinth seals, e.g the interlocking seal and the stepped seal, was numerically investigated. Preliminary calculation of the seal-cavity averaged pressure by using the one-dimensional control volume method showed favorable agreement with the experimental measurements. Subsequently, in-depth understanding of the fluid flow through the labyrinth seals was obtained by employing Computational Fluid Dynamics （CFD） and k -ε turbulence model, which resulted in a potential wealth of information like the streamline pattern, velocity vector field, and distribution of turbulent kinetic energy and static pressure. At the clearance of the seal the turbulent kinetic energy reached the peak value, while in the bulk region of the cavities it decayed fast. The static pressure rapidly dropped as the fluid flow went through the clearance; no distinct difference of the static pressure was inspected in the cavities. Also noted from the numerical results was that the stepped seal showed better sealing performance than the interlocking seal.展开更多
Numerical analysis of turbomachinery based on energy method is used to predict the aeroelastic stability of the straight-through labyrinth seal by solving aerodynamic work and vibration modes has been compared.It'...Numerical analysis of turbomachinery based on energy method is used to predict the aeroelastic stability of the straight-through labyrinth seal by solving aerodynamic work and vibration modes has been compared.It's found that the increase of pressure ratio leads to the in the circumferential direction of the labyrinth seal corresponds to the number of vibrating nodal diameters.In order to investigate the influence of structure parameters,the effect of relative thickness of the tooth tip,the width of the seal cavity and the eccentricity of the rotor on the aeroelastic stability of the labyrinth seal has been studied.The result of numerical calculation shows that the change of the structural parameters can affect the aeroelastic stability of the labyrinth seal to a certain extent,and can be applied in the structural optimization.展开更多
Preliminary design and simulation of a free piston engine suitable for small-scale energy production in distributed energy systems is presented in this paper.The properties,particularly the properties of gas seals of ...Preliminary design and simulation of a free piston engine suitable for small-scale energy production in distributed energy systems is presented in this paper.The properties,particularly the properties of gas seals of the engine are simulated using a simulation program developed for this case,and the results are utilized in preliminary main design parameter selection.The engine simulation program was developed by combining and modifying the source codes of the simulation and calculation programs obtained from Helsinki University of Technology,Tampere University of Technology,and Lappeenranta University of Technology.Because of the contact-free labyrinth seal used in the piston,the efficiency of the motor is lower than the efficiency of a conventional motor with oil lubricated piston rings.On the other hand,the lack of bearing losses,and the lack of losses associated with a crankshaft system and a gearbox,as well as the lack of lubrication oil expenses,compensates this effect.As a net result,this new motor would perform slightly better than the conventional one.Being completely oil-free,it is very environmentally friendly,and its exhaust gases are completely free of oil residuals which are causing problems in normal gas motors.展开更多
Experimental investigation has been done to evaluate the leakage performance of labyrinth seal for oil sealing on high-speed sealing test rig at different working and geometric parameters.Typical values of pressure ra...Experimental investigation has been done to evaluate the leakage performance of labyrinth seal for oil sealing on high-speed sealing test rig at different working and geometric parameters.Typical values of pressure ratio ranging from 1.0 to 2.0 were used and the rotating speed varied from 0 to 30,000 tpm.Dimensionless Taylor number was invited to response the effect of rotation.Oil was injected at the rate from 1.2 L/min to 2.8 L/min to check the sealing capacity.Leakage was measured at different seal configurations including sealing clearance,tooth tip thickness,pitch,teeth number,front inclined angle and oil-throwing angle.Different from gas sealing,the application of oil-throwing tooth in oil sealing attracted much interest as an obvious alternative to the conventional labyrinth seal.A blocking ring was captured during testing,which establishes understanding of underlying flow mechanisms in the clearance and plays an important role in oil sealing.There is a critical Taylor number at which the leakage coefficient drops drastically.After the critical Taylor number,a parabola rule appears.An optimal composition of tooth tip thickness,teeth number,oil-throwing angle and front inclined angle exists where the leakage performance behaves better.展开更多
The shrouded stator is widely used in aero-engines and the leakage flow from the cavity has a strong effect on the performance of the stator.Due to the high degree of geometric freedom of the tooth shape,it is difficu...The shrouded stator is widely used in aero-engines and the leakage flow from the cavity has a strong effect on the performance of the stator.Due to the high degree of geometric freedom of the tooth shape,it is difficult to find the optimal geometry directly through a large number of sample calculations.In this research,a multi-objective optimization design method was used for the structure of labyrinth seal teeth and the optimal shape was found.The effect of the optimal seal teeth on the stator was analyzed in a low-speed research compressor.It is found that two different optimized shapes of seal teethmeet the optimization requirements.There is a significant difference in the cavity depth,but they have similar intervals and angles of inclination of seal teeth.The total pressure loss coefficient below 20%span decreases by 9.18%and the outlet static pressure coefficient below 20%span increases by 1.76%.For both optimal results,the leakage flow becomes closer to the pressure side of the stator.The leakage flow climbs in the radial direction in the rear of the passage.The vortex near the suction side disappears.Instead,two vortexes with opposite rotating directions exist in the passage.The range of the vortex in the radial direction expands.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
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
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%.
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.
基金supported by National Key Technology R&D Program(2012BAB12B02)
文摘Experimental investigation of stepped and straight-through labyrinth seals was designed to study the sealing performance of two different typical labyrinth seals.In order to facilitate dimensional analysis on the flow resistance characteristics of labyrinth seals,the variable cross-section of the flow channels are considered as constant cross-section flow.The mechanical energy loss of flow caused by throttle turbulence intensity is considered as caused by friction along the way.The friction coefficient of stepped labyrinth seals is bigger than that of straight-through labyrinth seals by more than 40% for the same Reynolds number and the ratio of equivalent diameter and the seal length.The expression of friction coefficient /and /Re are obtained from experimental data.The verifications indicate that the expressions are highly accurate.The contribution to the total pressure drop of each tooth cavity gradually becomes less along the flow direction.
基金Project supported by the China Stat. High Tech. Project - "863" Project (Grant No. 2002AA526013-8).
文摘The leakage flow through two labyrinth seals, e.g the interlocking seal and the stepped seal, was numerically investigated. Preliminary calculation of the seal-cavity averaged pressure by using the one-dimensional control volume method showed favorable agreement with the experimental measurements. Subsequently, in-depth understanding of the fluid flow through the labyrinth seals was obtained by employing Computational Fluid Dynamics （CFD） and k -ε turbulence model, which resulted in a potential wealth of information like the streamline pattern, velocity vector field, and distribution of turbulent kinetic energy and static pressure. At the clearance of the seal the turbulent kinetic energy reached the peak value, while in the bulk region of the cavities it decayed fast. The static pressure rapidly dropped as the fluid flow went through the clearance; no distinct difference of the static pressure was inspected in the cavities. Also noted from the numerical results was that the stepped seal showed better sealing performance than the interlocking seal.
基金This work is supported by the National Nature ScienceFoundation of China(No.51475022).
文摘Numerical analysis of turbomachinery based on energy method is used to predict the aeroelastic stability of the straight-through labyrinth seal by solving aerodynamic work and vibration modes has been compared.It's found that the increase of pressure ratio leads to the in the circumferential direction of the labyrinth seal corresponds to the number of vibrating nodal diameters.In order to investigate the influence of structure parameters,the effect of relative thickness of the tooth tip,the width of the seal cavity and the eccentricity of the rotor on the aeroelastic stability of the labyrinth seal has been studied.The result of numerical calculation shows that the change of the structural parameters can affect the aeroelastic stability of the labyrinth seal to a certain extent,and can be applied in the structural optimization.
基金Project is financed by the Technology Development Center of Finland (Tekes)
文摘Preliminary design and simulation of a free piston engine suitable for small-scale energy production in distributed energy systems is presented in this paper.The properties,particularly the properties of gas seals of the engine are simulated using a simulation program developed for this case,and the results are utilized in preliminary main design parameter selection.The engine simulation program was developed by combining and modifying the source codes of the simulation and calculation programs obtained from Helsinki University of Technology,Tampere University of Technology,and Lappeenranta University of Technology.Because of the contact-free labyrinth seal used in the piston,the efficiency of the motor is lower than the efficiency of a conventional motor with oil lubricated piston rings.On the other hand,the lack of bearing losses,and the lack of losses associated with a crankshaft system and a gearbox,as well as the lack of lubrication oil expenses,compensates this effect.As a net result,this new motor would perform slightly better than the conventional one.Being completely oil-free,it is very environmentally friendly,and its exhaust gases are completely free of oil residuals which are causing problems in normal gas motors.
基金This work was supported by the National Natural Science Foundation of China(Grant No.51576193 and No.51706223).
文摘Experimental investigation has been done to evaluate the leakage performance of labyrinth seal for oil sealing on high-speed sealing test rig at different working and geometric parameters.Typical values of pressure ratio ranging from 1.0 to 2.0 were used and the rotating speed varied from 0 to 30,000 tpm.Dimensionless Taylor number was invited to response the effect of rotation.Oil was injected at the rate from 1.2 L/min to 2.8 L/min to check the sealing capacity.Leakage was measured at different seal configurations including sealing clearance,tooth tip thickness,pitch,teeth number,front inclined angle and oil-throwing angle.Different from gas sealing,the application of oil-throwing tooth in oil sealing attracted much interest as an obvious alternative to the conventional labyrinth seal.A blocking ring was captured during testing,which establishes understanding of underlying flow mechanisms in the clearance and plays an important role in oil sealing.There is a critical Taylor number at which the leakage coefficient drops drastically.After the critical Taylor number,a parabola rule appears.An optimal composition of tooth tip thickness,teeth number,oil-throwing angle and front inclined angle exists where the leakage performance behaves better.
基金support of the National Natural Science Foundation of China(No.52076129,No.51576124)the Shanghai Municipal Education Commission No.2022-04-5the Fundamental Research Funds for the Central Universities,and the United Innovation Center(UIC)of Aerothermal Technologies for Turbomachinery.
文摘The shrouded stator is widely used in aero-engines and the leakage flow from the cavity has a strong effect on the performance of the stator.Due to the high degree of geometric freedom of the tooth shape,it is difficult to find the optimal geometry directly through a large number of sample calculations.In this research,a multi-objective optimization design method was used for the structure of labyrinth seal teeth and the optimal shape was found.The effect of the optimal seal teeth on the stator was analyzed in a low-speed research compressor.It is found that two different optimized shapes of seal teethmeet the optimization requirements.There is a significant difference in the cavity depth,but they have similar intervals and angles of inclination of seal teeth.The total pressure loss coefficient below 20%span decreases by 9.18%and the outlet static pressure coefficient below 20%span increases by 1.76%.For both optimal results,the leakage flow becomes closer to the pressure side of the stator.The leakage flow climbs in the radial direction in the rear of the passage.The vortex near the suction side disappears.Instead,two vortexes with opposite rotating directions exist in the passage.The range of the vortex in the radial direction expands.
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.
