Computational Fluid Dynamics (CFD) simulations of cavitating flow through water hydraulic poppet valves were performed using advanced RNG k-epsilon turbulence model. The flow was turbulent, incompressible and unsteady...Computational Fluid Dynamics (CFD) simulations of cavitating flow through water hydraulic poppet valves were performed using advanced RNG k-epsilon turbulence model. The flow was turbulent, incompressible and unsteady, for Reynolds numbers greater than 43 000. The working fluid was water, and the structure of the valve was simplified as a two dimensional axisymmetric geometrical model. Flow field visualization was numerically achieved. The effects of inlet velocity, outlet pressure, opening size as well as poppet angle on cavitation intensity in the poppet valve were numerically investigated. Experimental flow visualization was conducted to capture cavitation images near the orifice in the poppet valve with 30° poppet angle using high speed video camera. The binary cavitating flow field distribution obtained from digital processing of the original cavitation image showed a good agreement with the numerical result.展开更多
Poppet valves are basic components of many manufacturing operations and industrial processes. The valve plug will withstand unbalanced pressure during the switching process due to the complex fluid-structure interacti...Poppet valves are basic components of many manufacturing operations and industrial processes. The valve plug will withstand unbalanced pressure during the switching process due to the complex fluid-structure interaction(FSI) in the local flow condition, especially with the occurrence of cavitation, which results in a convoluted generation and propagation of mechanical and fluid-dynamic vibrations. In the present work, computational fluid dynamics(CFD) approaches are proposed to model the flow-driven movement of the disc, in consideration of the valve stem rigidity, for a cryogenic poppet valve with liquid nitrogen as the working fluid. Cavitation effects are included in the CFD simulations. The relationship between the displacement of the disc and the resistance of the stem is obtained in advance using the finite element method(FEM), and implemented in CFD calculations based on the user-defined functions(UDFs). The disc vibration is realized using the dynamic mesh technology according to the resultant flow field force and resistance of the stem determined in the UDF. The vibration characteristics of the valve disc, including velocity and vibration frequency, are presented. The temporal evolutions of cavitation behavior due to the vibration are also captured. Comparisons of results between cavitation and non-cavitation conditions are made, and spectral analysis of the transient pressure fluctuations reveals that the presence of cavitation induces transient unbalanced loads on the valve disc and generates instantaneous tremendous pressure fluctuations in the flow field. Various pressure differences between the inlet and outlet as well as valve openings are modeled to probe the influences of FSI on valve disc vibration mechanisms.The consequent analysis gives deeper insights and improves understanding of the mechanism of the complicated interaction between the cavitating flow and the vibration of the valve disc.展开更多
The poppet valve is a fundamental component in fluid power systems. Under particular conditions, annoying ＂squeal＂ noises may be generated in hydraulic poppet valves. In the present study, the frequency spectrum of ...The poppet valve is a fundamental component in fluid power systems. Under particular conditions, annoying ＂squeal＂ noises may be generated in hydraulic poppet valves. In the present study, the frequency spectrum of the squeal noise is obtained by analyzing the sampling data from the accelerometer mounted on the valve body. It is found that the flow velocity, pressure, and structural parameters have crucial effects on the properties of squeal noise, especially frequency. Larger valve chamber volume or lower backpressure leads to lower fundamental frequency of the squeal noise. An explanation for the squeal noise, as a result of Helmholtz resonance, is suggested and proved by experimental results.展开更多
Two types of poppet valves were tested, one is a poppet with a sharp-edged seats, and the other is that with a chamfered seat. During the tests, the effects of backpressure and poppet lift on flow characteristics were...Two types of poppet valves were tested, one is a poppet with a sharp-edged seats, and the other is that with a chamfered seat. During the tests, the effects of backpressure and poppet lift on flow characteristics were considered. Cavitation inception was detected by the appearance and rapid growth of a particular low frequency component of the outlet pressure fluctuation of valve when cavitation occurs. Experimental results show cavitation, back pressure, valve opening and its geometrical shape have significant effects on the flow characteristics of valve. The flow coefficient of throttle with water used as working medium is 0 85～0 95 when there is no cavitation. The pressure drop of flow saturation decreases with the increasing of poppet lift. The sharp-edged throttle has stronger anti-cavitation ability than the chamfered one.展开更多
Poppet valves have become increasingly significant in ensuring precise digital flow rate and pressure control in hydraulic systems,necessitating a more profound understanding of the geometrical properties of cavitatio...Poppet valves have become increasingly significant in ensuring precise digital flow rate and pressure control in hydraulic systems,necessitating a more profound understanding of the geometrical properties of cavitation in them,as well as associated flow-choking conditions.Through a comparative analysis with experimentally observed cavity images,we found that large eddy simulation(LES)turbulence modeling effectively replicates the geometrical properties of cavitation in these valves.The analysis demonstrated that cavitation is generated from vortices that result from the interaction between the notch contracta flow and the surrounding fluid structure.Variations in the internal or external vena contracta conditions result in fixed or discrete cavities,and the length-to-diameter ratio serves as a measure of the transition between internal and external vena contracta flow properties.This study establishes a threshold length-to-diameter ratio of approximately 2 for the tested poppet valves.More specifically,in notch structures with a smaller valve opening,longer sealing length,and smaller throttling angle(corresponding to a larger length-to-diameter ratio),the liquid-to-vapor transfer process is more evident than that in the reverse direction.A long-standing vapor cavity becomes fixed inside the notch,leading to a more pronounced flow-choking phenomenon.In contrast,for structures with a smaller length-to-diameter ratio,the cavitation process for discrete vapor cavities is more complete,ensuring fluid flow continuity and significantly reducing the occurrence of the flow-choking phenomenon.展开更多
Surface finishing is essential for various applications in the aerospace industry.One of the applications is the poppet valve,which is used for leak-proof sealing of high-pressure gases in aerospace gas propulsion eng...Surface finishing is essential for various applications in the aerospace industry.One of the applications is the poppet valve,which is used for leak-proof sealing of high-pressure gases in aerospace gas propulsion engines.The combustion engine also typically employs a poppet valve as an intake and exhaust valve.Nano-finishing a poppet valve is difficult because of its complex narrow profile.The precise nano-finished poppet valve perfectly fits on its seat and reduces hydrocarbon emissions.The rotational-magnetorheological fluid-based finishing process can be used effectively for these complicated surfaces.The polishing agent in this process is magnetorheological fluid,and rheological properties are controlled by a permanent magnet.This article presents the uniform finishing of the poppet valve's narrow ridge profile,which is analyzed through finite element analysis(FEA),wherein the outcomes are uniform shear stress,normal stress,and magnetic flux density distributions along the poppet ridge profile.The study of forces exerting on abrasive grains and surface roughness simulation is also conducted using FEA findings.The experiment is subsequently performed to verify the simulation results for poppet profile polishing.The obtained experimental and simulated surface roughness values are comparable.After the finishing process,the maximum percentage improvement of surface roughness is obtained as 93.71%.The rotational-magnetorheological fluid-based finishing process has high accuracy and reliability for specific applications.展开更多
文摘Computational Fluid Dynamics (CFD) simulations of cavitating flow through water hydraulic poppet valves were performed using advanced RNG k-epsilon turbulence model. The flow was turbulent, incompressible and unsteady, for Reynolds numbers greater than 43 000. The working fluid was water, and the structure of the valve was simplified as a two dimensional axisymmetric geometrical model. Flow field visualization was numerically achieved. The effects of inlet velocity, outlet pressure, opening size as well as poppet angle on cavitation intensity in the poppet valve were numerically investigated. Experimental flow visualization was conducted to capture cavitation images near the orifice in the poppet valve with 30° poppet angle using high speed video camera. The binary cavitating flow field distribution obtained from digital processing of the original cavitation image showed a good agreement with the numerical result.
基金supported by the National Natural Science Foundation of China(Nos.51636007 and 51976177)the Key Research and Development Plan of Zhejiang Province(No.2020C01029),China。
文摘Poppet valves are basic components of many manufacturing operations and industrial processes. The valve plug will withstand unbalanced pressure during the switching process due to the complex fluid-structure interaction(FSI) in the local flow condition, especially with the occurrence of cavitation, which results in a convoluted generation and propagation of mechanical and fluid-dynamic vibrations. In the present work, computational fluid dynamics(CFD) approaches are proposed to model the flow-driven movement of the disc, in consideration of the valve stem rigidity, for a cryogenic poppet valve with liquid nitrogen as the working fluid. Cavitation effects are included in the CFD simulations. The relationship between the displacement of the disc and the resistance of the stem is obtained in advance using the finite element method(FEM), and implemented in CFD calculations based on the user-defined functions(UDFs). The disc vibration is realized using the dynamic mesh technology according to the resultant flow field force and resistance of the stem determined in the UDF. The vibration characteristics of the valve disc, including velocity and vibration frequency, are presented. The temporal evolutions of cavitation behavior due to the vibration are also captured. Comparisons of results between cavitation and non-cavitation conditions are made, and spectral analysis of the transient pressure fluctuations reveals that the presence of cavitation induces transient unbalanced loads on the valve disc and generates instantaneous tremendous pressure fluctuations in the flow field. Various pressure differences between the inlet and outlet as well as valve openings are modeled to probe the influences of FSI on valve disc vibration mechanisms.The consequent analysis gives deeper insights and improves understanding of the mechanism of the complicated interaction between the cavitating flow and the vibration of the valve disc.
基金Project supported by the National Natural Science Foundation of China （No. 51475415）, the Science Fund for Creative Research Groups of the National Natural Science Foundation of China （No. 51221004）, and the Fundamental Research Funds for the Central Universities, China
文摘The poppet valve is a fundamental component in fluid power systems. Under particular conditions, annoying ＂squeal＂ noises may be generated in hydraulic poppet valves. In the present study, the frequency spectrum of the squeal noise is obtained by analyzing the sampling data from the accelerometer mounted on the valve body. It is found that the flow velocity, pressure, and structural parameters have crucial effects on the properties of squeal noise, especially frequency. Larger valve chamber volume or lower backpressure leads to lower fundamental frequency of the squeal noise. An explanation for the squeal noise, as a result of Helmholtz resonance, is suggested and proved by experimental results.
文摘Two types of poppet valves were tested, one is a poppet with a sharp-edged seats, and the other is that with a chamfered seat. During the tests, the effects of backpressure and poppet lift on flow characteristics were considered. Cavitation inception was detected by the appearance and rapid growth of a particular low frequency component of the outlet pressure fluctuation of valve when cavitation occurs. Experimental results show cavitation, back pressure, valve opening and its geometrical shape have significant effects on the flow characteristics of valve. The flow coefficient of throttle with water used as working medium is 0 85～0 95 when there is no cavitation. The pressure drop of flow saturation decreases with the increasing of poppet lift. The sharp-edged throttle has stronger anti-cavitation ability than the chamfered one.
基金supported by the National Natural Science Foundation of China(Nos.52075387 and 52375060)the Shanghai Natural Science Foundation of China(No.22ZR1464400)+2 种基金the National Key R&D Program of China(No.2019YFB2005102)the Shanghai Municipal Science and Technology Major Project(No.2021SHZDZX0100)the Fundamental Research Funds for the Central Universities(No.2022-1-ZD-04),China.
文摘Poppet valves have become increasingly significant in ensuring precise digital flow rate and pressure control in hydraulic systems,necessitating a more profound understanding of the geometrical properties of cavitation in them,as well as associated flow-choking conditions.Through a comparative analysis with experimentally observed cavity images,we found that large eddy simulation(LES)turbulence modeling effectively replicates the geometrical properties of cavitation in these valves.The analysis demonstrated that cavitation is generated from vortices that result from the interaction between the notch contracta flow and the surrounding fluid structure.Variations in the internal or external vena contracta conditions result in fixed or discrete cavities,and the length-to-diameter ratio serves as a measure of the transition between internal and external vena contracta flow properties.This study establishes a threshold length-to-diameter ratio of approximately 2 for the tested poppet valves.More specifically,in notch structures with a smaller valve opening,longer sealing length,and smaller throttling angle(corresponding to a larger length-to-diameter ratio),the liquid-to-vapor transfer process is more evident than that in the reverse direction.A long-standing vapor cavity becomes fixed inside the notch,leading to a more pronounced flow-choking phenomenon.In contrast,for structures with a smaller length-to-diameter ratio,the cavitation process for discrete vapor cavities is more complete,ensuring fluid flow continuity and significantly reducing the occurrence of the flow-choking phenomenon.
基金SERB(Science and Engineering Research Board)India(project No.EEQ/2017/000597)EPSRC(Engineering and Physical Science Research Council)UK(Grant Ref:EP/W524244/1)fortheirfinancial assistance.
文摘Surface finishing is essential for various applications in the aerospace industry.One of the applications is the poppet valve,which is used for leak-proof sealing of high-pressure gases in aerospace gas propulsion engines.The combustion engine also typically employs a poppet valve as an intake and exhaust valve.Nano-finishing a poppet valve is difficult because of its complex narrow profile.The precise nano-finished poppet valve perfectly fits on its seat and reduces hydrocarbon emissions.The rotational-magnetorheological fluid-based finishing process can be used effectively for these complicated surfaces.The polishing agent in this process is magnetorheological fluid,and rheological properties are controlled by a permanent magnet.This article presents the uniform finishing of the poppet valve's narrow ridge profile,which is analyzed through finite element analysis(FEA),wherein the outcomes are uniform shear stress,normal stress,and magnetic flux density distributions along the poppet ridge profile.The study of forces exerting on abrasive grains and surface roughness simulation is also conducted using FEA findings.The experiment is subsequently performed to verify the simulation results for poppet profile polishing.The obtained experimental and simulated surface roughness values are comparable.After the finishing process,the maximum percentage improvement of surface roughness is obtained as 93.71%.The rotational-magnetorheological fluid-based finishing process has high accuracy and reliability for specific applications.
