The evolution of the coherent structures in a two-dimensional time-developing mixing layer of the FENE-P fluids is examined numerically. By the means of an appropriate filtering for the polymer stress, some characteri...The evolution of the coherent structures in a two-dimensional time-developing mixing layer of the FENE-P fluids is examined numerically. By the means of an appropriate filtering for the polymer stress, some characteristics of the coherent structures at high b were obtained, which Azaiez and Homsy did not address. The results indicate that adding polymer to the Newtonian fluids will cause stronger vorticity diffusion, accompanied with weaker fundamental and subharmonical perturbations and slower rotational motion of neighbouring vortices during pairing. This effect decreases with the Weissenberg number, but increases with b. In addition, the time when the consecutive rollers are completely coalesced into one delays in the viscoelastic mixing layer compared with the Newtonian one of the same total viscosity.展开更多
The Falkner-Skan boundary layer steady flow over a flat stretching sheet is investigated in this paper.The mathematical model consists of continuity and the momentum equations, while a new model is proposed for MHD Fi...The Falkner-Skan boundary layer steady flow over a flat stretching sheet is investigated in this paper.The mathematical model consists of continuity and the momentum equations, while a new model is proposed for MHD Finitely Extensible Nonlinear Elastic Peterlin(FENE-P) fluid. The effects of Hall current with the variation of intensity of non-zero pressure gradient are taken into account. The governing partial differential equations are first transformed to ordinary differential equations using appropriate similarity transformation and then solved by Adomian decomposition method(ADM). The obtained results are validated by generalized collocation method(GCM) and found to be in good agreement. Effects of pertinent parameters are discussed through graphs and tables. Comparison with the existing studies is made as a limiting case of the considered problem at the end.展开更多
The rheological properties of salt-tolerant partially hydrolyzed polyacrylamide(HPAM)solutions with molecular of 2.5×107 g/mol at different concentrations were measured in steady-state shear flow mode by Haake Rh...The rheological properties of salt-tolerant partially hydrolyzed polyacrylamide(HPAM)solutions with molecular of 2.5×107 g/mol at different concentrations were measured in steady-state shear flow mode by Haake Rheostress 150 rheometer.Three constitutive equations(Oldroyd four constant model,Guesekus model and FENE-P model) were used for describing the apparent viscosity and first normal stress difference.The apparent viscosity of salt-tolerant HPAM solutions appears a first Newtonian zone when the shear rate is approximately lower than 0.2 s-1.At high shear rate,the HPAM solutions show shear-thinning and elasticity.The results show that the FENE-P model has the best agreement between theoretical and experimental data within the available shear rate range.The material parameters are useful for numerical analysis of polymer solution flow fields.展开更多
<Abstract>The influence of rheological parameters on vortex dynamics and the extent of drag reduction(DR) were deciphered via extensively analyzing the hi-fidelity direct numerical simulation results of the turb...<Abstract>The influence of rheological parameters on vortex dynamics and the extent of drag reduction(DR) were deciphered via extensively analyzing the hi-fidelity direct numerical simulation results of the turbulent channel flow with polymer solutions.It has been observed that in all drag reduction regimes from the onset of DR to maximum drag reduction(MDR) limit,the Deborah number is defined as the product of an effective Weissenberg number,and the root mean square streamwise vorticity fluctuation remains O(1) in the near wall region.The ratio of the average lifetime of axial vortices to the vortex rotating duration decreases with increasing DR,and MDR is achieved when these time scales become nearly equal.Based on these observations a simple framework is proposed adequately to describe the influence of polymer additives on the extent of DR from onset to MDR as well as the universality of the MDR in flow systems with polymer additives.展开更多
Problems involving fluid flexible-structure interactions(FFSI)are ubiquitous in engineering and sciences.Peskin’s immersed boundary(IB)method is the first framework for modeling and simulation of such problems.This p...Problems involving fluid flexible-structure interactions(FFSI)are ubiquitous in engineering and sciences.Peskin’s immersed boundary(IB)method is the first framework for modeling and simulation of such problems.This paper addresses a three-dimensional extension of the IB framework for non-Newtonian fluids which include power-law fluid,Oldroyd-B fluid,and FENE-P fluid.The motion of the non-Newtonian fluids are modelled by the lattice Boltzmann equations(D3Q19 model).The differential constitutive equations of Oldroyd-B and FENE-P fluids are solved by the D3Q7 model.Numerical results indicate that the new method is first-order accurate and conditionally stable.To show the capability of the new method,it is tested on three FFSI toy problems:a power-law fluid past a flexible sheet fixed at its midline,a flexible sheet being flapped periodically at its midline in an Oldroyd-B fluid,and a flexible sheet being rotated at one edge in a FENE-P fluid.展开更多
In this work,the drag-reducing mechanism of high-Reynoldsnumber turbulent channel flow with surfactant additives is investigated by using large eddy simulation(LES)method.An N-parallel finitely extensible nonlinear el...In this work,the drag-reducing mechanism of high-Reynoldsnumber turbulent channel flow with surfactant additives is investigated by using large eddy simulation(LES)method.An N-parallel finitely extensible nonlinear elastic model with Peterlin’s approximation(FENE-P)is used to describe the rheological behaviors of non-Newtonian fluid with surfactant.To close the filtered LES equations,a hybrid subgrid scale(SGS)model coupling the spatial filter and temporal filter is applied to compute the subgrid stress and other subfilter terms.The finite difference method and projection algorithm are adopted to solve the LES governing equations.To validate the correctness of our LES method and in-house code,the particle image velocimetry(PIV)experiment is carried out and representative measured results are compared with LES results in detail.Then the flow characteristics and drag-reducing mechanism of turbulent channel flow with surfactant are investigated from the perspective of drag reduction rate,mean velocity,fluctuation of deformation rate,shear stress,transport and dissipation of turbulent kinetic energy,and turbulent coherent structures.This research can shed a light on the application of turbulent drag reduction technique in district heating,petroleum transport,etc.展开更多
A collocated finite volume method on unstructured meshes is introduced to simulate the viscoelastic flow of the polymer melt with viscous dissipation past a confined cylinder.The constitutive equation for the simulati...A collocated finite volume method on unstructured meshes is introduced to simulate the viscoelastic flow of the polymer melt with viscous dissipation past a confined cylinder.The constitutive equation for the simulations is non-isothermal FENE-P model,which is derived from the molecular theories.The temperature effect on the macroscopic fields(e.g.,velocity,stress) and microscopic fields(e.g.,molecular orientation,deformation,stretch) is investigated by comparison of isothermal and non-isothermal situations.This investigation indicates that temperature rise caused by viscous dissipation should not be neglected since it has significant effect on the macroscopic and microscopic properties of the polymer melt.展开更多
文摘The evolution of the coherent structures in a two-dimensional time-developing mixing layer of the FENE-P fluids is examined numerically. By the means of an appropriate filtering for the polymer stress, some characteristics of the coherent structures at high b were obtained, which Azaiez and Homsy did not address. The results indicate that adding polymer to the Newtonian fluids will cause stronger vorticity diffusion, accompanied with weaker fundamental and subharmonical perturbations and slower rotational motion of neighbouring vortices during pairing. This effect decreases with the Weissenberg number, but increases with b. In addition, the time when the consecutive rollers are completely coalesced into one delays in the viscoelastic mixing layer compared with the Newtonian one of the same total viscosity.
文摘The Falkner-Skan boundary layer steady flow over a flat stretching sheet is investigated in this paper.The mathematical model consists of continuity and the momentum equations, while a new model is proposed for MHD Finitely Extensible Nonlinear Elastic Peterlin(FENE-P) fluid. The effects of Hall current with the variation of intensity of non-zero pressure gradient are taken into account. The governing partial differential equations are first transformed to ordinary differential equations using appropriate similarity transformation and then solved by Adomian decomposition method(ADM). The obtained results are validated by generalized collocation method(GCM) and found to be in good agreement. Effects of pertinent parameters are discussed through graphs and tables. Comparison with the existing studies is made as a limiting case of the considered problem at the end.
基金Project(IFP-A-2022-2-5-24) supported by Ministry of Education and University of Hafr Al Batin, Saudi ArabiaProject supported by University of Campania “Luigi Vanvitelli”, ItalyProject supported by COMSATS University Islamabad, Pakistan。
基金Project(07JCZDJC02600) supported by the Natural Science Foundation ofTianjin,China
文摘The rheological properties of salt-tolerant partially hydrolyzed polyacrylamide(HPAM)solutions with molecular of 2.5×107 g/mol at different concentrations were measured in steady-state shear flow mode by Haake Rheostress 150 rheometer.Three constitutive equations(Oldroyd four constant model,Guesekus model and FENE-P model) were used for describing the apparent viscosity and first normal stress difference.The apparent viscosity of salt-tolerant HPAM solutions appears a first Newtonian zone when the shear rate is approximately lower than 0.2 s-1.At high shear rate,the HPAM solutions show shear-thinning and elasticity.The results show that the FENE-P model has the best agreement between theoretical and experimental data within the available shear rate range.The material parameters are useful for numerical analysis of polymer solution flow fields.
基金Project (10672069) supported by the National Natural Science Foundation of China
文摘<Abstract>The influence of rheological parameters on vortex dynamics and the extent of drag reduction(DR) were deciphered via extensively analyzing the hi-fidelity direct numerical simulation results of the turbulent channel flow with polymer solutions.It has been observed that in all drag reduction regimes from the onset of DR to maximum drag reduction(MDR) limit,the Deborah number is defined as the product of an effective Weissenberg number,and the root mean square streamwise vorticity fluctuation remains O(1) in the near wall region.The ratio of the average lifetime of axial vortices to the vortex rotating duration decreases with increasing DR,and MDR is achieved when these time scales become nearly equal.Based on these observations a simple framework is proposed adequately to describe the influence of polymer additives on the extent of DR from onset to MDR as well as the universality of the MDR in flow systems with polymer additives.
基金The work is supported by the US National Science Foundation(NSF)through the research grant DMS-1522554We thank the unknown Reviewers for their helpful suggestions and comments which have helped us.
文摘Problems involving fluid flexible-structure interactions(FFSI)are ubiquitous in engineering and sciences.Peskin’s immersed boundary(IB)method is the first framework for modeling and simulation of such problems.This paper addresses a three-dimensional extension of the IB framework for non-Newtonian fluids which include power-law fluid,Oldroyd-B fluid,and FENE-P fluid.The motion of the non-Newtonian fluids are modelled by the lattice Boltzmann equations(D3Q19 model).The differential constitutive equations of Oldroyd-B and FENE-P fluids are solved by the D3Q7 model.Numerical results indicate that the new method is first-order accurate and conditionally stable.To show the capability of the new method,it is tested on three FFSI toy problems:a power-law fluid past a flexible sheet fixed at its midline,a flexible sheet being flapped periodically at its midline in an Oldroyd-B fluid,and a flexible sheet being rotated at one edge in a FENE-P fluid.
基金This research was supported by the Beijing Natural Science Foundation(3204038)the National Natural Science Foundation of China(51904031,51936001)the Jointly Projects of Beijing Natural Science Foundation and Beijing Municipal Education Commission(KZ201810017023).
文摘In this work,the drag-reducing mechanism of high-Reynoldsnumber turbulent channel flow with surfactant additives is investigated by using large eddy simulation(LES)method.An N-parallel finitely extensible nonlinear elastic model with Peterlin’s approximation(FENE-P)is used to describe the rheological behaviors of non-Newtonian fluid with surfactant.To close the filtered LES equations,a hybrid subgrid scale(SGS)model coupling the spatial filter and temporal filter is applied to compute the subgrid stress and other subfilter terms.The finite difference method and projection algorithm are adopted to solve the LES governing equations.To validate the correctness of our LES method and in-house code,the particle image velocimetry(PIV)experiment is carried out and representative measured results are compared with LES results in detail.Then the flow characteristics and drag-reducing mechanism of turbulent channel flow with surfactant are investigated from the perspective of drag reduction rate,mean velocity,fluctuation of deformation rate,shear stress,transport and dissipation of turbulent kinetic energy,and turbulent coherent structures.This research can shed a light on the application of turbulent drag reduction technique in district heating,petroleum transport,etc.
基金Supported by the National Natural Science Foundation of China（10590353 10871159） the National Basic Research Program of China（2005CB321704） the Doctoral Foundation of Northwestern Polytechnical University（CX200817）
文摘A collocated finite volume method on unstructured meshes is introduced to simulate the viscoelastic flow of the polymer melt with viscous dissipation past a confined cylinder.The constitutive equation for the simulations is non-isothermal FENE-P model,which is derived from the molecular theories.The temperature effect on the macroscopic fields(e.g.,velocity,stress) and microscopic fields(e.g.,molecular orientation,deformation,stretch) is investigated by comparison of isothermal and non-isothermal situations.This investigation indicates that temperature rise caused by viscous dissipation should not be neglected since it has significant effect on the macroscopic and microscopic properties of the polymer melt.
