Y. X. Huang, P. H. Chung, K. M. Chung, C. Y. Huang
Vortex generators (VGs) are typically positioned upstream of a boundary layer separation region. Their effectiveness depends on incoming flow conditions (Mach number, Reynolds number and boundary layer characteristics), geometrical configuration (vane or ramp, height, width, and angle of incidence) and spacing. Device-induced vortices and following decay allow VGs to be used as a passive control device. This study uses pressure-sensitive paint (PSP) to determine the global surface pressure pattern for a flat plate flow in the presence of VGs (counter-rotating vanes, co-rotating vanes and ramps). The freestream Mach number is 0.64 and 0.83. The ratio between the height of the VGs and the incoming boundary layer thickness is 0.2, 0.5 and 1.0. The standard deviation in the spanwise pressure in the streamwise direction is used to determine the downstream influence of turbulent flow past VGs. Increasing the height of VGs causes device-induced vortices to propagate farther downstream.
{"title":"Downstream influence of turbulent flow past vortex generators","authors":"Y. X. Huang, P. H. Chung, K. M. Chung, C. Y. Huang","doi":"10.1093/jom/ufad039","DOIUrl":"https://doi.org/10.1093/jom/ufad039","url":null,"abstract":"\u0000 Vortex generators (VGs) are typically positioned upstream of a boundary layer separation region. Their effectiveness depends on incoming flow conditions (Mach number, Reynolds number and boundary layer characteristics), geometrical configuration (vane or ramp, height, width, and angle of incidence) and spacing. Device-induced vortices and following decay allow VGs to be used as a passive control device. This study uses pressure-sensitive paint (PSP) to determine the global surface pressure pattern for a flat plate flow in the presence of VGs (counter-rotating vanes, co-rotating vanes and ramps). The freestream Mach number is 0.64 and 0.83. The ratio between the height of the VGs and the incoming boundary layer thickness is 0.2, 0.5 and 1.0. The standard deviation in the spanwise pressure in the streamwise direction is used to determine the downstream influence of turbulent flow past VGs. Increasing the height of VGs causes device-induced vortices to propagate farther downstream.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2023-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138599485","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This study established a Computational Fluid Dynamics (CFD) model based on a dynamic mesh strategy to conduct a comprehensive numerical investigation of the performance of the E1619 propeller in open water tests. To capture the turbulence flows around the propeller, a large eddy simulation (LES) turbulence model was implemented. In order to validate the simulation results, a series of open water tests were conducted in the towing tank at National Cheng Kung University, resulting in a successful achievement of total uncertainties of less than approximately 6%. The approach of simultaneous grid and time refinement was utilized to perform the discretization analysis. Eventually, the simulation results were employed to analyze the hydrodynamic performance and flow structure around the propeller, resulting in a conclusion based on the attained level of accuracy. The results indicate that the cases for a propeller with a strut exhibit favorable predictions compared to those of a single propeller, with error values for the thrust coefficients and propeller efficiencies falling below 6%. On the other hand, the torque coefficient was more accurately estimated for the cases of a single propeller than for those of a propeller with a strut, with error values below 2%.
{"title":"The CFD Simulation of E1619 Propeller Open Water Tests Validated by the EFD in the NCKU Towing Tank","authors":"Yu-Hsin Lin, Ahmad Darori Hasan","doi":"10.1093/jom/ufad034","DOIUrl":"https://doi.org/10.1093/jom/ufad034","url":null,"abstract":"This study established a Computational Fluid Dynamics (CFD) model based on a dynamic mesh strategy to conduct a comprehensive numerical investigation of the performance of the E1619 propeller in open water tests. To capture the turbulence flows around the propeller, a large eddy simulation (LES) turbulence model was implemented. In order to validate the simulation results, a series of open water tests were conducted in the towing tank at National Cheng Kung University, resulting in a successful achievement of total uncertainties of less than approximately 6%. The approach of simultaneous grid and time refinement was utilized to perform the discretization analysis. Eventually, the simulation results were employed to analyze the hydrodynamic performance and flow structure around the propeller, resulting in a conclusion based on the attained level of accuracy. The results indicate that the cases for a propeller with a strut exhibit favorable predictions compared to those of a single propeller, with error values for the thrust coefficients and propeller efficiencies falling below 6%. On the other hand, the torque coefficient was more accurately estimated for the cases of a single propeller than for those of a propeller with a strut, with error values below 2%.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2023-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139266200","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract Based on the symplectic superposition method, the free vibration models of rectangular and right-angle triangle plates on the Winkler elastic foundation are established in present paper, and the modes and frequencies are studied. In addition, the theoretical calculation model and finite element analysis model of rectangular thin plate and right-angle triangle plate on elastic foundation are established by using Mathematica software and ABAQUS software. It proves that the symplectic superposition method converges very fast and has a good consistency with the finite element simulation results. Analytical results show that foundation stiffness, aspect ratio and boundary condition have great influences on vibration frequency and mode shape for structures. This paper solved the free vibration problem of rectangular plate and right-angle triangle plate on elastic foundation by using symplectic superposition method. Compared with the inverse or semi-inverse method, this method avoids the process of assuming the form about the solution, hence the result of this method is completely rational.
{"title":"Analytical solutions of free vibration for rectangular thin plate and right-angle triangle plate on the Winkler elastic foundation based on the symplectic superposition method","authors":"Hao-Jie Jiang, Tong-Bo Chen, Yu-Xiang Ren, Ning-Hua Gao","doi":"10.1093/jom/ufad032","DOIUrl":"https://doi.org/10.1093/jom/ufad032","url":null,"abstract":"Abstract Based on the symplectic superposition method, the free vibration models of rectangular and right-angle triangle plates on the Winkler elastic foundation are established in present paper, and the modes and frequencies are studied. In addition, the theoretical calculation model and finite element analysis model of rectangular thin plate and right-angle triangle plate on elastic foundation are established by using Mathematica software and ABAQUS software. It proves that the symplectic superposition method converges very fast and has a good consistency with the finite element simulation results. Analytical results show that foundation stiffness, aspect ratio and boundary condition have great influences on vibration frequency and mode shape for structures. This paper solved the free vibration problem of rectangular plate and right-angle triangle plate on elastic foundation by using symplectic superposition method. Compared with the inverse or semi-inverse method, this method avoids the process of assuming the form about the solution, hence the result of this method is completely rational.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135291658","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract In this paper, the free vibration of Timoshenko pipes conveying fluid with gravity and different boundary conditions is analyzed by using the weak form quadrature element method. The dimensionless frequency and critical flow velocity have been calculated considering various parameters such as the mass ratio of pipe to fluid, slenderness ratio, and gravity. The numerical results with different numbers of discrete points are tested, and the results show that the method has a fast convergence speed. Some numerical results are compared with the existing literature, which proves that the weak form quadrature element method has high accuracy and computational efficiency. This paper shows that the weak form quadrature element method is a preferred method for analyzing fluid-conveying pipes with various boundary conditions.
{"title":"Free vibration analysis of Timoshenko pipes conveying fluid with gravity and different boundary conditions","authors":"Bo Shui, Yun-dong Li, Yu-mei Luo, Fei Luo","doi":"10.1093/jom/ufad031","DOIUrl":"https://doi.org/10.1093/jom/ufad031","url":null,"abstract":"Abstract In this paper, the free vibration of Timoshenko pipes conveying fluid with gravity and different boundary conditions is analyzed by using the weak form quadrature element method. The dimensionless frequency and critical flow velocity have been calculated considering various parameters such as the mass ratio of pipe to fluid, slenderness ratio, and gravity. The numerical results with different numbers of discrete points are tested, and the results show that the method has a fast convergence speed. Some numerical results are compared with the existing literature, which proves that the weak form quadrature element method has high accuracy and computational efficiency. This paper shows that the weak form quadrature element method is a preferred method for analyzing fluid-conveying pipes with various boundary conditions.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135291790","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract A steady granular flow down an inclined surface is an important flow configuration to study the dynamic of dry granular flow. This work adopts two-dimensional discrete element simulation to study how inter-grain friction may play a role in momentum transport, in addition to the collision-based transport, to induce the non-Bagnold flow velocity profile reported in the literature. Special efforts were made to apply the knowledge of network science to identify the contact force chain network from particle dynamics information using the graph theory with the Louvain greedy algorithm. We studied how the number of grains born in the force chain network grows when the flow scaled velocity profile degrades from Bagnold to non-Bagnold flows. Concurrently, the stress loading ratio carried by these frictional contacts rises abruptly upon the non-Bagnold flow transition identifies when the flow Froude number falls roughly below 2.15. Both phenomena suggest that the non-local phenomenon of Bagnold velocity profile degradation occurs when sufficient grains are confined in the force chain network to assist the stress transport, replacing the collisional transport. Hence, a refined rheology model is needed in the future to account for this friction-assisted momentum transport at a mesoscopic yet flow-dependent length scale like that of the currently investigated force network.
{"title":"Growth of force chain network upon non-Bagnold Transition of Inclined Surface Granular Flows via Discrete Element Simulation","authors":"Cheng-Ting Tsai, Chih-Ying Cheng, F-L Yang","doi":"10.1093/jom/ufad030","DOIUrl":"https://doi.org/10.1093/jom/ufad030","url":null,"abstract":"Abstract A steady granular flow down an inclined surface is an important flow configuration to study the dynamic of dry granular flow. This work adopts two-dimensional discrete element simulation to study how inter-grain friction may play a role in momentum transport, in addition to the collision-based transport, to induce the non-Bagnold flow velocity profile reported in the literature. Special efforts were made to apply the knowledge of network science to identify the contact force chain network from particle dynamics information using the graph theory with the Louvain greedy algorithm. We studied how the number of grains born in the force chain network grows when the flow scaled velocity profile degrades from Bagnold to non-Bagnold flows. Concurrently, the stress loading ratio carried by these frictional contacts rises abruptly upon the non-Bagnold flow transition identifies when the flow Froude number falls roughly below 2.15. Both phenomena suggest that the non-local phenomenon of Bagnold velocity profile degradation occurs when sufficient grains are confined in the force chain network to assist the stress transport, replacing the collisional transport. Hence, a refined rheology model is needed in the future to account for this friction-assisted momentum transport at a mesoscopic yet flow-dependent length scale like that of the currently investigated force network.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135291659","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Anum Tanveer, Zain Ul Abidin, Faisal Z Duraihem, S Saleem
Abstract Cilia is an important mechanism for epithelial cells in the respiratory tract, cerebrospinal flow in the brain, hair bundles in the ear and photoreceptor in the retina, etc. Cilia can also be found in human fallopian tube for the transport of the ova, embryos and sperm. In this research, we investigate the combined effects of mixed convection and magnetic field. In the present analysis we describe the flow and heat transfer characteristics of MHD Carreau fluid in fallopian tube with metachronal wave of cilia. The mathematical Eq. of the problem is performed under creeping phenomena and long wavelength approximation. The numerical solution for extra stress tensor, temperature profile and streamline pattern are obtained using the NDSolve method of Mathematica software. The physical and graphical behavior of different value of involved parameter are discussed in the last section. The parametric values are kept small (< 10) in view of cilia walls having very small diameter.
{"title":"Flow and heat transfer characteristics in fallopian tube with metachronal wave of cilia","authors":"Anum Tanveer, Zain Ul Abidin, Faisal Z Duraihem, S Saleem","doi":"10.1093/jom/ufad027","DOIUrl":"https://doi.org/10.1093/jom/ufad027","url":null,"abstract":"Abstract Cilia is an important mechanism for epithelial cells in the respiratory tract, cerebrospinal flow in the brain, hair bundles in the ear and photoreceptor in the retina, etc. Cilia can also be found in human fallopian tube for the transport of the ova, embryos and sperm. In this research, we investigate the combined effects of mixed convection and magnetic field. In the present analysis we describe the flow and heat transfer characteristics of MHD Carreau fluid in fallopian tube with metachronal wave of cilia. The mathematical Eq. of the problem is performed under creeping phenomena and long wavelength approximation. The numerical solution for extra stress tensor, temperature profile and streamline pattern are obtained using the NDSolve method of Mathematica software. The physical and graphical behavior of different value of involved parameter are discussed in the last section. The parametric values are kept small (&lt; 10) in view of cilia walls having very small diameter.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135853467","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract Space debris impacts on whipped shields are dominantly non-vertical. Shock initiation and interaction govern the fragmentation of projectiles and plates, directly determining the features of the produced debris cloud. During the initial impact stage of a projectile on a target, wave propagation and evolution occur in their interior with co-dominant material fragmentation. In this study, the effects of the impact conditions (impact velocity and attack angle) on the critical conditions for jet generation were examined based on the asymmetric jetting theory. In the Geometric Propagation Model (GPM), the effect of the attack angle was considered, and a wave front deflection angle parameter was introduced. The modified GPM could describe the geometric features and position of a wave front during an oblique impact. Combined with smoothed particle hydrodynamics numerical simulations, the interior of projectiles, fragmentation features, and pressure attenuation were studied. It was found that in large attack angle cases, the projectile material is more likely to reach the critical conditions for jet generation, and the jet mass proportion of the projectile material increases with increasing attack angle. The modified GPM is an oblique elliptic Eq. that is a function of the equivalent speed, impact velocity, attack angle, time, and deflection angle. It may be applicable to hypervelocity events involving any monolithic material as long as the equivalent speed and deflection angle can be provided from numerical simulations. The impact conditions exhibit a quantitative relationship with the pressure attenuation in a projectile, among which the impact velocity has a more significant effect. This study established a quantitative analysis method for initial impact stage of the oblique hypervelocity impact of a spherical projectile on a flat plate.
{"title":"Jetting and shock wave during oblique hypervelocity impact of spherical projectile","authors":"Xin Liu, Yongjun Deng, Ken Wen, Yong Yao","doi":"10.1093/jom/ufad012","DOIUrl":"https://doi.org/10.1093/jom/ufad012","url":null,"abstract":"Abstract Space debris impacts on whipped shields are dominantly non-vertical. Shock initiation and interaction govern the fragmentation of projectiles and plates, directly determining the features of the produced debris cloud. During the initial impact stage of a projectile on a target, wave propagation and evolution occur in their interior with co-dominant material fragmentation. In this study, the effects of the impact conditions (impact velocity and attack angle) on the critical conditions for jet generation were examined based on the asymmetric jetting theory. In the Geometric Propagation Model (GPM), the effect of the attack angle was considered, and a wave front deflection angle parameter was introduced. The modified GPM could describe the geometric features and position of a wave front during an oblique impact. Combined with smoothed particle hydrodynamics numerical simulations, the interior of projectiles, fragmentation features, and pressure attenuation were studied. It was found that in large attack angle cases, the projectile material is more likely to reach the critical conditions for jet generation, and the jet mass proportion of the projectile material increases with increasing attack angle. The modified GPM is an oblique elliptic Eq. that is a function of the equivalent speed, impact velocity, attack angle, time, and deflection angle. It may be applicable to hypervelocity events involving any monolithic material as long as the equivalent speed and deflection angle can be provided from numerical simulations. The impact conditions exhibit a quantitative relationship with the pressure attenuation in a projectile, among which the impact velocity has a more significant effect. This study established a quantitative analysis method for initial impact stage of the oblique hypervelocity impact of a spherical projectile on a flat plate.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135785988","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
De-Shin Liu, Po-Chun Wen, Z. Zhuang, Y. Chao, Pei-Chen Huang
The temperature dependence mechanical characteristics of 4N Cu wire with 25, 30, and 38 μm diameters are investigated via the utilization of micro-tensile tests. Measured data revealed that the concerned mechanical characteristics, Young's modulus and yield stresses, are significantly degraded under high testing temperature, and the variation of aforementioned characteristics degradation are almost linear proportional to the temperature increment. Trapezoidal and standard triangle loop formation of Cu wire is simulated based on the finite element method, the simulated looping profiles of Cu wires is compared to the Au wires and the Cu wire is regarded as the improved solution for the high loop height wire formation. Moreover, the Johnson-Cook constitutive model is utilized to describe the plasticity of Cu wire in accordance with the experimental data under different temperature level consideration. Accordingly, the comprehensive mechanical characteristics investigation of 4N Cu wire is systemically demonstrated and explored.
{"title":"Temperature-Dependence Mechanical Characteristics Investigation of Cu Wire and Corresponding High Strain Rate Plasticity Behaviors Enabled by Johnson-Cook Constitutive Model","authors":"De-Shin Liu, Po-Chun Wen, Z. Zhuang, Y. Chao, Pei-Chen Huang","doi":"10.1093/jom/ufad020","DOIUrl":"https://doi.org/10.1093/jom/ufad020","url":null,"abstract":"\u0000 The temperature dependence mechanical characteristics of 4N Cu wire with 25, 30, and 38 μm diameters are investigated via the utilization of micro-tensile tests. Measured data revealed that the concerned mechanical characteristics, Young's modulus and yield stresses, are significantly degraded under high testing temperature, and the variation of aforementioned characteristics degradation are almost linear proportional to the temperature increment. Trapezoidal and standard triangle loop formation of Cu wire is simulated based on the finite element method, the simulated looping profiles of Cu wires is compared to the Au wires and the Cu wire is regarded as the improved solution for the high loop height wire formation. Moreover, the Johnson-Cook constitutive model is utilized to describe the plasticity of Cu wire in accordance with the experimental data under different temperature level consideration. Accordingly, the comprehensive mechanical characteristics investigation of 4N Cu wire is systemically demonstrated and explored.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2023-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43656352","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Joint structures made from plates or shells are frequently used in large constructions, such as oil storage tanks in petrochemical industries. The corrosion-induced metal loss often appears on the back side of the bottom plate supported by ground or sand. The welding residual stress and weight of shell walls accelerate the corrosion. Determining the severity of metal loss under the joint is challenging. This work uses the mode pair technique for nondestructive inspection of inaccessible regions in joint structures. A finite element analysis model simulates the transient responses of the incident and mode-converted fundamental and second harmonic plate waves. The second harmonic s0 plate wave satisfying the phase velocity matching condition accompanies the transmitted fundamental SH0 plate wave. A directional filter identifies every mode-converted plate wave by comparing the frequency spectra with the dispersion curves. Linear ultrasonic guided waves can detect inaccessible regions using mode-converted reflections. The symmetry of the linear mode-converted fundamental plate waves depends on the defect position and geometry, not the size. The mode-converted second harmonic guided wave can achieve better spatial resolution for defect sizing. The nonlinear parameter shows a proportional trend with an increasing thickness reduction. Experimental and numerical evidence reveals nonlinear ultrasonic guided wave technique has the potential for defect detection in joint structures.
{"title":"Nonlinear Ultrasonic Characterization of Joint Structures Using Backscatter Guided Waves","authors":"Wenqiu Wu, C. Yin","doi":"10.1093/jom/ufad022","DOIUrl":"https://doi.org/10.1093/jom/ufad022","url":null,"abstract":"\u0000 Joint structures made from plates or shells are frequently used in large constructions, such as oil storage tanks in petrochemical industries. The corrosion-induced metal loss often appears on the back side of the bottom plate supported by ground or sand. The welding residual stress and weight of shell walls accelerate the corrosion. Determining the severity of metal loss under the joint is challenging. This work uses the mode pair technique for nondestructive inspection of inaccessible regions in joint structures. A finite element analysis model simulates the transient responses of the incident and mode-converted fundamental and second harmonic plate waves. The second harmonic s0 plate wave satisfying the phase velocity matching condition accompanies the transmitted fundamental SH0 plate wave. A directional filter identifies every mode-converted plate wave by comparing the frequency spectra with the dispersion curves. Linear ultrasonic guided waves can detect inaccessible regions using mode-converted reflections. The symmetry of the linear mode-converted fundamental plate waves depends on the defect position and geometry, not the size. The mode-converted second harmonic guided wave can achieve better spatial resolution for defect sizing. The nonlinear parameter shows a proportional trend with an increasing thickness reduction. Experimental and numerical evidence reveals nonlinear ultrasonic guided wave technique has the potential for defect detection in joint structures.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2023-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42524555","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The main purpose of this study is to numerically investigate the effect of pin-fin NACA airfoil on the heat transfer performance of a single open microchannel heat sink with a fixed surface area and a constant wall heat flux. It was found that the helical flow within the microchannel and the converging-diverging flow near the two sides of the microchannel, caused by the periodically arranged NACA airfoil shaped pin fins with an attack angle, dominate the overall heat dissipation ability of the heat sink. The heat dissipation ability can be further improved by increasing the attack angle and Reynolds number. Of the airfoils considered, the symmetrical airfoil NACA0012 in no attack angle case presents the smallest pressure drop, but also the smallest thermal performance value, which can still achieve a Nusselt number improvement of 35.15% and a thermal performance factor (TPF) improvement of 1.38%, compared to the no-fin case. The NACA airfoil effect can be improved when asymmetric airfoils are considered. In terms of overall thermal performance, the NACA6412 would be the best choice. Its percentage increases in the Nusselt number and TPF can be further enhanced by up to 57.62% and 35.43%, respectively, compared to the no-attack-angle NACA0012 case.
{"title":"Thermal Performance of Open Microchannel Heat Sink with NACA Airfoil Shaped PIN Fins","authors":"Kun-Da Wu, H. Weng","doi":"10.1093/jom/ufad019","DOIUrl":"https://doi.org/10.1093/jom/ufad019","url":null,"abstract":"\u0000 The main purpose of this study is to numerically investigate the effect of pin-fin NACA airfoil on the heat transfer performance of a single open microchannel heat sink with a fixed surface area and a constant wall heat flux. It was found that the helical flow within the microchannel and the converging-diverging flow near the two sides of the microchannel, caused by the periodically arranged NACA airfoil shaped pin fins with an attack angle, dominate the overall heat dissipation ability of the heat sink. The heat dissipation ability can be further improved by increasing the attack angle and Reynolds number. Of the airfoils considered, the symmetrical airfoil NACA0012 in no attack angle case presents the smallest pressure drop, but also the smallest thermal performance value, which can still achieve a Nusselt number improvement of 35.15% and a thermal performance factor (TPF) improvement of 1.38%, compared to the no-fin case. The NACA airfoil effect can be improved when asymmetric airfoils are considered. In terms of overall thermal performance, the NACA6412 would be the best choice. Its percentage increases in the Nusselt number and TPF can be further enhanced by up to 57.62% and 35.43%, respectively, compared to the no-attack-angle NACA0012 case.","PeriodicalId":50136,"journal":{"name":"Journal of Mechanics","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2023-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49622826","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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