This Freeman Scholar article reviews the formulation and application of a kinetic theory for modeling the transport and dispersion of small particles in turbulent gas-flows. The theory has been developed and refined by numerous authors and now forms a rational basis for modeling complex particle laden flows. The formalism and methodology of this approach are discussed and the choice of closure of the kinetic equations involved ensures realizability and well posedness with exact closure for Gaussian carrier flow fields. The historical development is presented and how single-particle kinetic equations resolve the problem of closure of the transport equations for particle mass, momentum, and kinetic energy/stress (the so-called continuum equations) and the treatment of the dispersed phase as a fluid. The mass fluxes associated with the turbulent aerodynamic driving forces and interfacial stresses are shown to be both dispersive and convective in inhomogeneous turbulence with implications for the build-up of particles concentration in near wall turbulent boundary layers and particle pair concentration at small separation. It is shown how this approach deals with the natural wall boundary conditions for a flowing particle suspension and examples are given of partially absorbing surfaces with particle scattering and gravitational settling; how this approach has revealed the existence of contra gradient diffusion in a developing shear flow and the influence of the turbulence on gravitational settling (the Maxey effect). Particular consideration is given to the general problem of particle transport and deposition in turbulent boundary layers including particle resuspension. Finally, the application of a particle pair formulation for both monodisperse and bidisperse particle flows is reviewed where the differences between the two are compared through the influence of collisions on the particle continuum equations and the particle collision kernel for the clustering of particles and the degree of random uncorrelated motion (RUM) at the small scales of the turbulence. The inclusion of bidisperse particle suspensions implies the application to polydisperse flows and the evolution of particle size distribution.
{"title":"The Development and Application of a Kinetic Theory for Modeling Dispersed Particle Flows","authors":"M. Reeks","doi":"10.1115/1.4051289","DOIUrl":"https://doi.org/10.1115/1.4051289","url":null,"abstract":"\u0000 This Freeman Scholar article reviews the formulation and application of a kinetic theory for modeling the transport and dispersion of small particles in turbulent gas-flows. The theory has been developed and refined by numerous authors and now forms a rational basis for modeling complex particle laden flows. The formalism and methodology of this approach are discussed and the choice of closure of the kinetic equations involved ensures realizability and well posedness with exact closure for Gaussian carrier flow fields. The historical development is presented and how single-particle kinetic equations resolve the problem of closure of the transport equations for particle mass, momentum, and kinetic energy/stress (the so-called continuum equations) and the treatment of the dispersed phase as a fluid. The mass fluxes associated with the turbulent aerodynamic driving forces and interfacial stresses are shown to be both dispersive and convective in inhomogeneous turbulence with implications for the build-up of particles concentration in near wall turbulent boundary layers and particle pair concentration at small separation. It is shown how this approach deals with the natural wall boundary conditions for a flowing particle suspension and examples are given of partially absorbing surfaces with particle scattering and gravitational settling; how this approach has revealed the existence of contra gradient diffusion in a developing shear flow and the influence of the turbulence on gravitational settling (the Maxey effect). Particular consideration is given to the general problem of particle transport and deposition in turbulent boundary layers including particle resuspension. Finally, the application of a particle pair formulation for both monodisperse and bidisperse particle flows is reviewed where the differences between the two are compared through the influence of collisions on the particle continuum equations and the particle collision kernel for the clustering of particles and the degree of random uncorrelated motion (RUM) at the small scales of the turbulence. The inclusion of bidisperse particle suspensions implies the application to polydisperse flows and the evolution of particle size distribution.","PeriodicalId":54833,"journal":{"name":"Journal of Fluids Engineering-Transactions of the Asme","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2021-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80901975","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Hemodynamic Study of Blood Flow in the Carotid Artery with a Focus on Carotid Sinus Using Fluid-Structure Interaction","authors":"Aditya Bantwal, A. Singh, A. Menon, Nitesh Kumar","doi":"10.1115/1.4051902","DOIUrl":"https://doi.org/10.1115/1.4051902","url":null,"abstract":"","PeriodicalId":54833,"journal":{"name":"Journal of Fluids Engineering-Transactions of the Asme","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2021-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76697696","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ali Hassannejadmoghaddam, B. Kutschelis, F. Holz, Tomas Börjesson, R. Skoda
{"title":"3D Flow Simulation of a Twin-Screw Pump for the Analysis of Gap Flow Characteristics","authors":"Ali Hassannejadmoghaddam, B. Kutschelis, F. Holz, Tomas Börjesson, R. Skoda","doi":"10.1115/1.4051730","DOIUrl":"https://doi.org/10.1115/1.4051730","url":null,"abstract":"","PeriodicalId":54833,"journal":{"name":"Journal of Fluids Engineering-Transactions of the Asme","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2021-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73105786","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The slant angle plays a crucial role in the flow property of hatchback ground vehicles. An optimum slant angle is obligatory for better handling the ground vehicles when fitted with a rear wing. In this regard, the variation of time-averaged flow properties around a wing-attached hatchback ground vehicle (Ahmed body) due to a variable slant angle is accessed by this paper. The design includes a scaled Ahmed body as a reference ground vehicle and a rear wing with NACA 0018 profile. The computational studies are executed with Reynolds-averaged Navier–Stokes based k-epsilon turbulence model with nonequilibrium wall function. The vehicle's model is scaled to 75% of the actual model, and analyses are conducted with Reynolds number 2.7 × 106. After the study, it is observed that a 15 deg slant angle is the critical angle for the wing attached state in which the drag coefficient is maximum. After this angle, a sudden reduction of coefficients is observed, where 25 deg is critical for without wing condition. Besides this, the two counter-rotating horseshoe vortices in the separation bubble and side edge c-pillar vortices also behave differently due to the wing's presence. The turbulent kinetic energy variation and the variation in coefficients of surface pressure are also affected by the rear wing attachment. This paper will assist in finding the optimum slant angle for hatchback ground vehicles in the presence of a rear wing. Thus the study will help in increasing stability and control for hatchback ground vehicles.
{"title":"Effect of Rear Wing on Time-Averaged Ground Vehicle Wake With Variable Slant Angle","authors":"S. Uddin, F. Rashid","doi":"10.1115/1.4050373","DOIUrl":"https://doi.org/10.1115/1.4050373","url":null,"abstract":"\u0000 The slant angle plays a crucial role in the flow property of hatchback ground vehicles. An optimum slant angle is obligatory for better handling the ground vehicles when fitted with a rear wing. In this regard, the variation of time-averaged flow properties around a wing-attached hatchback ground vehicle (Ahmed body) due to a variable slant angle is accessed by this paper. The design includes a scaled Ahmed body as a reference ground vehicle and a rear wing with NACA 0018 profile. The computational studies are executed with Reynolds-averaged Navier–Stokes based k-epsilon turbulence model with nonequilibrium wall function. The vehicle's model is scaled to 75% of the actual model, and analyses are conducted with Reynolds number 2.7 × 106. After the study, it is observed that a 15 deg slant angle is the critical angle for the wing attached state in which the drag coefficient is maximum. After this angle, a sudden reduction of coefficients is observed, where 25 deg is critical for without wing condition. Besides this, the two counter-rotating horseshoe vortices in the separation bubble and side edge c-pillar vortices also behave differently due to the wing's presence. The turbulent kinetic energy variation and the variation in coefficients of surface pressure are also affected by the rear wing attachment. This paper will assist in finding the optimum slant angle for hatchback ground vehicles in the presence of a rear wing. Thus the study will help in increasing stability and control for hatchback ground vehicles.","PeriodicalId":54833,"journal":{"name":"Journal of Fluids Engineering-Transactions of the Asme","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2021-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82477223","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In the present research, we address the implications of the pulsating electric field on controlling mass flow-rate characteristics for the time-periodic electro-osmotic flow of a viscoelastic fluid through a microchannel. Going beyond the Debye-Hückel linearization for the potential distribution inside the Electric Double Layer, the Phan-Thien-Tanner constitutive model is employed to describe the viscoelastic behaviour of the fluid. The analytical/semi-analytical expressions for the velocity distribution corresponding to a steady basic part, and a transient perturbed part are obtained by considering periodic pulsations in the applied electrical field. Our results based on sinusoidal pulsations reveal that enhanced shear thinning characteristics of the viscoelastic fluids show higher amplitude of pulsations with the oscillations in the velocity gradients primarily contrived within the Electric Double Layer region. The amplitude of mass flow rates increases with increasing the viscoelastic parameter , whereas, the phase lag displays a reverse trend. The analysis for an inverse problem is extended where the required magnitude of electric field pulsations for a target mass flow rate in the form of sinusoidal pulsations. It is found that with increasing shear-thinning characteristics of the viscoelastic fluid, there is a progressive reduction in the required electric field strength to maintain an aimed mass flow rate. Besides, required electric fields for controlled mass flow with triangular and trapezoidal pulsations are also determined.
在本研究中，我们讨论了脉动电场对粘弹性流体通过微通道的时间周期电渗透流动的质量流率特性控制的影响。本文采用Phan-Thien-Tanner本构模型来描述流体的粘弹性行为，超越了双电层内部电位分布的debye - h ckel线性化。考虑外加电场的周期脉动，得到了稳态基部和瞬态摄动部速度分布的解析/半解析表达式。我们基于正弦脉动的结果表明，粘弹性流体的剪切减薄特性增强，在双电层区域内主要设计的速度梯度振荡中，脉动幅度更高。质量流量的幅值随粘弹性参数的增大而增大，而相位滞后则呈相反趋势。推广了反问题的分析，其中以正弦脉动的形式给出了目标质量流量所需的电场脉动幅度。研究发现，随着粘弹性流体剪切减薄特性的增强，维持目标质量流量所需的电场强度逐渐减小。此外，还确定了具有三角形和梯形脉动的受控质量流所需电场。
{"title":"Control of Mass Flow-Rate of Viscoelastic Fluids Through Time-Periodic Electro-Osmotic Flows in a Microchannel","authors":"Sayantan Dawn, S. Sarkar","doi":"10.1115/1.4051429","DOIUrl":"https://doi.org/10.1115/1.4051429","url":null,"abstract":"\u0000 In the present research, we address the implications of the pulsating electric field on controlling mass flow-rate characteristics for the time-periodic electro-osmotic flow of a viscoelastic fluid through a microchannel. Going beyond the Debye-Hückel linearization for the potential distribution inside the Electric Double Layer, the Phan-Thien-Tanner constitutive model is employed to describe the viscoelastic behaviour of the fluid. The analytical/semi-analytical expressions for the velocity distribution corresponding to a steady basic part, and a transient perturbed part are obtained by considering periodic pulsations in the applied electrical field. Our results based on sinusoidal pulsations reveal that enhanced shear thinning characteristics of the viscoelastic fluids show higher amplitude of pulsations with the oscillations in the velocity gradients primarily contrived within the Electric Double Layer region. The amplitude of mass flow rates increases with increasing the viscoelastic parameter , whereas, the phase lag displays a reverse trend. The analysis for an inverse problem is extended where the required magnitude of electric field pulsations for a target mass flow rate in the form of sinusoidal pulsations. It is found that with increasing shear-thinning characteristics of the viscoelastic fluid, there is a progressive reduction in the required electric field strength to maintain an aimed mass flow rate. Besides, required electric fields for controlled mass flow with triangular and trapezoidal pulsations are also determined.","PeriodicalId":54833,"journal":{"name":"Journal of Fluids Engineering-Transactions of the Asme","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2021-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89562657","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This work deals with the effects of suction and injection on Casson nanofluid around a moving wedge under the influence of gyrotactic micro-organisms along with viscous and ohmic dissipation. The governing system of highly coupled nonlinear partial differential equations together with assisting boundary conditions is converted by applying suitable similarity transformations, into a set of nonlinear ordinary differential equations. The obtained flow model is solved numerically by bvp4c (matlab) procedure. The accuracy of the flow model under consideration is validated by employing another well-known mathematical technique Runge–Kutta-Fehlberg (RKF) having good agreement while comparing the numerical results obtained by bvp4c for both suction and injection cases. Impacts of various pertinent parameters active in the flow model such as thermophoresis and Brownian motion, moving wedge, magnetic field, viscous and ohmic dissipation are numerically calculated for both suction and injection flow situations and also presented graphically. It is observed that the increase in casson parameter enhances the velocity but declines the density of motile organism, concentration and temperature for suction as well as injection flow case. The impacts of mass transfer rate of gyrotactic micro-organisms, Nusselt and Sherwood numbers for various fluid parameters are numerically presented in tabular form, separately for both suction and injection. One of the important observations of this study is that the suction or injection plays a key role in controlling boundary layer flow and brings stability in the flow. Moreover, rate of heat and mass transfer get enhanced in the existence of gyrotactic micro-organisms. Further, it would be worth mentioning that physical behavior of this flow problem coincides very well with already published literature either graphically or in tabular representation.
{"title":"Suction and Injection Impacts on Casson Nanofluid With Gyrotactic Micro-organisms Over a Moving Wedge","authors":"K. Jabeen, M. Mushtaq, R. Akram","doi":"10.1115/1.4051484","DOIUrl":"https://doi.org/10.1115/1.4051484","url":null,"abstract":"\u0000 This work deals with the effects of suction and injection on Casson nanofluid around a moving wedge under the influence of gyrotactic micro-organisms along with viscous and ohmic dissipation. The governing system of highly coupled nonlinear partial differential equations together with assisting boundary conditions is converted by applying suitable similarity transformations, into a set of nonlinear ordinary differential equations. The obtained flow model is solved numerically by bvp4c (matlab) procedure. The accuracy of the flow model under consideration is validated by employing another well-known mathematical technique Runge–Kutta-Fehlberg (RKF) having good agreement while comparing the numerical results obtained by bvp4c for both suction and injection cases. Impacts of various pertinent parameters active in the flow model such as thermophoresis and Brownian motion, moving wedge, magnetic field, viscous and ohmic dissipation are numerically calculated for both suction and injection flow situations and also presented graphically. It is observed that the increase in casson parameter enhances the velocity but declines the density of motile organism, concentration and temperature for suction as well as injection flow case. The impacts of mass transfer rate of gyrotactic micro-organisms, Nusselt and Sherwood numbers for various fluid parameters are numerically presented in tabular form, separately for both suction and injection. One of the important observations of this study is that the suction or injection plays a key role in controlling boundary layer flow and brings stability in the flow. Moreover, rate of heat and mass transfer get enhanced in the existence of gyrotactic micro-organisms. Further, it would be worth mentioning that physical behavior of this flow problem coincides very well with already published literature either graphically or in tabular representation.","PeriodicalId":54833,"journal":{"name":"Journal of Fluids Engineering-Transactions of the Asme","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2021-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74120211","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Qian-qian Li, Cheng-shuo Wu, B. Qian, Peng Wu, Bin Huang, Dazhuan Wu
As a specific radial flow pump, the regenerative flow pump (RFP) usually has a low efficiency. In this study, in order to explore the matching mechanism, three cases with various matching relations were investigated by the methods of theoretical calculation, computational fluids dynamics (CFD) simulation, and experiment test. The results illustrate that the theoretical prediction, numerical simulation, and experimental data are in good agreement. Furthermore, when the matching relation expressed by a ratio of the channel's and blade's radial length is equal to 1, the geometrical profiles of RFP can well guide the circulation flow into the channel at large radii and into the impeller at small radii, forming intense longitudinal vortex. The steady, strong exchange flow is characterized by the inflow and outflow regions approximately half of the isosurface. The axial vortex motion without apparent flow separation and irregular flow is observed in the impeller, a low velocity annulus exists in the medium radii of the impeller without other distinct velocity clouds, and a low velocity strip and a high velocity annulus in the channel are, respectively, performed along the blade's pressure surface and the channel's outer radii. All of this corresponds to the best pump's performance and the largest efficiency of the impeller and channel. This work promotes a systematical understanding of the matching mechanism between impeller and flow channel in the RFP and could provide some reference for the design and performance optimization for RFP.
{"title":"Investigation of the Matching Relation Between Impeller and Flow Channel of Regenerative Flow Pumps","authors":"Qian-qian Li, Cheng-shuo Wu, B. Qian, Peng Wu, Bin Huang, Dazhuan Wu","doi":"10.1115/1.4050009","DOIUrl":"https://doi.org/10.1115/1.4050009","url":null,"abstract":"\u0000 As a specific radial flow pump, the regenerative flow pump (RFP) usually has a low efficiency. In this study, in order to explore the matching mechanism, three cases with various matching relations were investigated by the methods of theoretical calculation, computational fluids dynamics (CFD) simulation, and experiment test. The results illustrate that the theoretical prediction, numerical simulation, and experimental data are in good agreement. Furthermore, when the matching relation expressed by a ratio of the channel's and blade's radial length is equal to 1, the geometrical profiles of RFP can well guide the circulation flow into the channel at large radii and into the impeller at small radii, forming intense longitudinal vortex. The steady, strong exchange flow is characterized by the inflow and outflow regions approximately half of the isosurface. The axial vortex motion without apparent flow separation and irregular flow is observed in the impeller, a low velocity annulus exists in the medium radii of the impeller without other distinct velocity clouds, and a low velocity strip and a high velocity annulus in the channel are, respectively, performed along the blade's pressure surface and the channel's outer radii. All of this corresponds to the best pump's performance and the largest efficiency of the impeller and channel. This work promotes a systematical understanding of the matching mechanism between impeller and flow channel in the RFP and could provide some reference for the design and performance optimization for RFP.","PeriodicalId":54833,"journal":{"name":"Journal of Fluids Engineering-Transactions of the Asme","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2021-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80987877","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Numerical investigations are carried out in a single-stage subsonic axial flow compressor to unravel the influence of blade tip surface roughness on the tip leakage flow characteristics and hence the compressor performance. The studies were carried out at different tip clearance of 0.38τ, 0.77τ, 1.15τ, and 1.54τ and blade tip surface roughness of 0.31ε and 0.62ε. The tip clearance of 0.38τ with blade tip surface roughness of 0.62ε resulted in the highest stall margin and pressure rise of 20.3% and 4.3%, respectively. The compressor blade loading was found to be improved by 5.9% after incorporating the blade tip surface roughness. The isosurfaces of vorticity contour plotted using the Q-criterion showed the reduction in strength of the tip leakage vortex. The tip leakage trajectory was found to be shifted toward the suction surface of the blade for the blade tip with surface roughness. This positive alteration in the tip leakage flow structure led to the improved performance for the blade tip with surface roughness.
{"title":"Influence of Blade Tip Surface Roughness on the Performance of a Single-Stage Axial Flow Compressor","authors":"Pradyumna Kodancha, P. Salunkhe","doi":"10.1115/1.4049935","DOIUrl":"https://doi.org/10.1115/1.4049935","url":null,"abstract":"\u0000 Numerical investigations are carried out in a single-stage subsonic axial flow compressor to unravel the influence of blade tip surface roughness on the tip leakage flow characteristics and hence the compressor performance. The studies were carried out at different tip clearance of 0.38τ, 0.77τ, 1.15τ, and 1.54τ and blade tip surface roughness of 0.31ε and 0.62ε. The tip clearance of 0.38τ with blade tip surface roughness of 0.62ε resulted in the highest stall margin and pressure rise of 20.3% and 4.3%, respectively. The compressor blade loading was found to be improved by 5.9% after incorporating the blade tip surface roughness. The isosurfaces of vorticity contour plotted using the Q-criterion showed the reduction in strength of the tip leakage vortex. The tip leakage trajectory was found to be shifted toward the suction surface of the blade for the blade tip with surface roughness. This positive alteration in the tip leakage flow structure led to the improved performance for the blade tip with surface roughness.","PeriodicalId":54833,"journal":{"name":"Journal of Fluids Engineering-Transactions of the Asme","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2021-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85418925","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Zeng Yongshun, Z. Yao, Zhang Shijie, Fujun Wang, R. Xiao
Tip clearance in hydraulic machines may complicate the fluid–structure interaction (FSI) effects. In this investigation, a mode-based approach (modal work) is evaluated and employed to quantitatively predict the added mass, added stiffness, and hydrodynamic damping ratio, in relation to the first-order bending mode of a vibrating hydrofoil. The investigated relative tip clearance ranges from 0.067% to 2% of the span length. The predicted vortex shedding frequency, natural frequency, and hydrodynamic damping ratio of the hydrofoil are in good agreement with the previously published experimental results, with relative deviations within 9.92%, 6.97%, and 11.23%, respectively. Simulation results show that the added mass, added stiffness, and hydrodynamic damping ratio increase inversely as the tip clearance increases. In particular, as the relative tip clearance increases from 0.067% to 2%, the added mass in still water, the added stiffness, and hydrodynamic damping ratio at a velocity of 10 m/s decrease by 18.66%, 9.36%, and 27.99%, respectively. As the tip clearance increases, the inversely increased pressure difference between the upper and lower surfaces of the vibrating hydrofoil is the main reason for the inversely increased hydrodynamic damping ratio. This is due to the energy leakages via the tip clearance region increase as the tip clearance increases, which may cause less fluid force to resist the vibration of the hydrofoil, resulting in less negative modal work done by the fluid load on the hydrofoil.
{"title":"Influence of Tip Clearance on the Hydrodynamic Damping Characteristics of a Hydrofoil","authors":"Zeng Yongshun, Z. Yao, Zhang Shijie, Fujun Wang, R. Xiao","doi":"10.1115/1.4049675","DOIUrl":"https://doi.org/10.1115/1.4049675","url":null,"abstract":"Tip clearance in hydraulic machines may complicate the fluid–structure interaction (FSI) effects. In this investigation, a mode-based approach (modal work) is evaluated and employed to quantitatively predict the added mass, added stiffness, and hydrodynamic damping ratio, in relation to the first-order bending mode of a vibrating hydrofoil. The investigated relative tip clearance ranges from 0.067% to 2% of the span length. The predicted vortex shedding frequency, natural frequency, and hydrodynamic damping ratio of the hydrofoil are in good agreement with the previously published experimental results, with relative deviations within 9.92%, 6.97%, and 11.23%, respectively. Simulation results show that the added mass, added stiffness, and hydrodynamic damping ratio increase inversely as the tip clearance increases. In particular, as the relative tip clearance increases from 0.067% to 2%, the added mass in still water, the added stiffness, and hydrodynamic damping ratio at a velocity of 10 m/s decrease by 18.66%, 9.36%, and 27.99%, respectively. As the tip clearance increases, the inversely increased pressure difference between the upper and lower surfaces of the vibrating hydrofoil is the main reason for the inversely increased hydrodynamic damping ratio. This is due to the energy leakages via the tip clearance region increase as the tip clearance increases, which may cause less fluid force to resist the vibration of the hydrofoil, resulting in less negative modal work done by the fluid load on the hydrofoil.","PeriodicalId":54833,"journal":{"name":"Journal of Fluids Engineering-Transactions of the Asme","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2021-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79817864","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
New criteria for fully resolving two-phase flow regime transitions using direct numerical simulation with the level set method for interface capturing are proposed. A series of flows chosen to capture small scale interface phenomena are simulated at different grid refinements. These cases include droplet deformation and breakup in a simple shear field, the thin film around a Taylor bubble, and the rise of a bubble toward a free surface. These cases cover the major small scale phenomena observed in two-phase flows: internal recirculation, interface curvature, interface snapping, flow of liquid in thin films, and drainage/snapping of thin films. The results from these simulations and their associated grid studies were used to develop new meshing requirements for simulation of two-phase flow using interface capturing methods, in particular the level set method. When applicable, the code used in this work, PHASTA, was compared to experiments in order to contribute to the ongoing validation process of the code. Results show that when the solver meets these criteria, with the exception of resolving the nanometer scale liquid film between coalescing bubbles, the code is capable of accurately simulating interface topology changes.
{"title":"Evaluation of Length Scales and Meshing Requirements for Resolving Two-Phase Flow Regime Transitions Using the Level Set Method","authors":"M. Zimmer, I. Bolotnov","doi":"10.1115/1.4049934","DOIUrl":"https://doi.org/10.1115/1.4049934","url":null,"abstract":"\u0000 New criteria for fully resolving two-phase flow regime transitions using direct numerical simulation with the level set method for interface capturing are proposed. A series of flows chosen to capture small scale interface phenomena are simulated at different grid refinements. These cases include droplet deformation and breakup in a simple shear field, the thin film around a Taylor bubble, and the rise of a bubble toward a free surface. These cases cover the major small scale phenomena observed in two-phase flows: internal recirculation, interface curvature, interface snapping, flow of liquid in thin films, and drainage/snapping of thin films. The results from these simulations and their associated grid studies were used to develop new meshing requirements for simulation of two-phase flow using interface capturing methods, in particular the level set method. When applicable, the code used in this work, PHASTA, was compared to experiments in order to contribute to the ongoing validation process of the code. Results show that when the solver meets these criteria, with the exception of resolving the nanometer scale liquid film between coalescing bubbles, the code is capable of accurately simulating interface topology changes.","PeriodicalId":54833,"journal":{"name":"Journal of Fluids Engineering-Transactions of the Asme","volume":null,"pages":null},"PeriodicalIF":2.0,"publicationDate":"2021-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80639858","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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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