Drag reduction phenomenon in pipelines has received lots of attention during the past decades due to its potential engineering applications, especially in fluid transporting industries. Various methods to enhance drag...Drag reduction phenomenon in pipelines has received lots of attention during the past decades due to its potential engineering applications, especially in fluid transporting industries. Various methods to enhance drag reduction have been developed throughout the years and divided into two categories;non-additives method and additives method. Both categories have different types of methods, with different formulations and applications which will generally be discussed in this review. Among all the methods discussed, drag reduction using polymer additive is as one of the most enticing and desirable methods. It has been the subject of research in this field and has been studied extensively for quite some time. It is due to its ability to reduce drag up to 80% when added in minute concentrations. Reducing drag in the pipe will require less pumping power thus offering economic relieves to the industries. So, this paper will be focusing more on the use of polymer additives as drag reducing agent, the general formulations of the additives, major issues involving the use of drag reducing polymers, and the potential applications of it. However, despite the extensive works of drag reduction polymer, there are still no models that accurately explain the mechanism of drag reduction. More studies needed to be done to have a better understanding of the phenomenon. Therefore, future research areas and potential approaches are proposed for future work.展开更多
Direct numerical simulations （DNS） were performed for the forced homogeneous isotropic turbulence （FHIT） with/without polymer additives in order to elaborate the characteristics of the turbulent energy cascading i...Direct numerical simulations （DNS） were performed for the forced homogeneous isotropic turbulence （FHIT） with/without polymer additives in order to elaborate the characteristics of the turbulent energy cascading influenced by drag-reducing effects. The finite elastic non-linear extensibility-Peterlin model （FENE-P） was used as the conformation tensor equation for the viscoelastic polymer solution. Detailed analyses of DNS data were carried out in this paper for the turbulence scaling law and the topological dynamics of FHIT as well as the important turbulent parameters, including turbulent kinetic energy spectra, enstrophy and strain, velocity structure function, small-scale intermittency, etc. A natural and straightforward definition for the drag reduction rate was also proposed for the drag-reducing FHIT based on the decrease degree of the turbulent kinetic energy. It was found that the turbulent energy cascading in the FHIT was greatly modified by the drag-reducing polymer additives. The enstrophy and the strain fields in the FH1T of the polymer solution were remarkably weakened as compared with their Newtonian counterparts. The small-scale vortices and the small-scale intermittency were all inhibited by the viscoelastic effects in the FHIT of the polymer solution. However, the scaling law in a fashion of extended self-similarity for the FHIT of the polymer solution, within the presently simulated range of Weissenberg numbers, had no distinct differences compared with that of the Newtonian fluid case.展开更多
In this work, a rheological study of automotive lubricant oils, neutral light paraffinic (NLP) and neutral medium paraffinic (NMP), additivated with two commercial viscosity index improvers-VIIs, based on hydrogenated...In this work, a rheological study of automotive lubricant oils, neutral light paraffinic (NLP) and neutral medium paraffinic (NMP), additivated with two commercial viscosity index improvers-VIIs, based on hydrogenated poly (isoprene-co-styrene), at different concentrations, was carried out. The study included the determination of the kinematic viscosity of the mixtures, the calculation of the viscosity indexes and their behavior when subjected to various rheometric experiments, including stress sweep, steady state flow, creep and recovery, and temperature ramp oscillatory tests. The obtained results showed the efficacy of the additives as viscosity index improvers, enabling a significant increase in the viscosity index of the pure oils at relatively low concentrations. The determination of the storage (G’) and of the loss (G”) moduli for the mixtures oil/VII additives showed a large predominance of the viscous effect over the elastic one. Except when under low shear stress, the mixtures showed a pseudoplastic behavior, with the flow curves being adjusted to fit the Ostwald-de-Waele model (Power Law), with negative flow behavior indexes.展开更多
Large-eddy simulations （LES） based on the temporal approximate deconvolution model were performed for a forced homogeneous isotropic turbulence （FHIT） with polymer additives at moderate Taylor Reynolds number. Fin...Large-eddy simulations （LES） based on the temporal approximate deconvolution model were performed for a forced homogeneous isotropic turbulence （FHIT） with polymer additives at moderate Taylor Reynolds number. Finitely extensible nonlinear elastic in the Peterlin approximation model was adopted as the constitutive equation for the filtered conformation tensor of the polymer molecules. The LES results were verified through comparisons with the direct numerical simulation results. Using the LES database of the FHIT in the Newtonian fluid and the polymer solution flows, the polymer effects on some important parameters such as strain, vorticity, drag reduction, and so forth were studied. By extracting the vortex structures and exploring the flatness factor through a high-order correlation function of velocity derivative and wavelet analysis, it can be found that the small-scale vortex structures and small-scale intermittency in the FHIT are all inhibited due to the existence of the polymers. The extended self-similarity scaling law in the polymer solution flow shows no apparent difference from that in the Newtonian fluid flow at the currently simulated ranges of Reynolds and Weissenberg numbers.展开更多
基金supported by the Ministry of Higher Education, Malaysia [grant number FRG0416-TK-1/2015]UMSGreat funding from Universiti Malaysia Sabah [grant number GUG0052-TK2/2016]
文摘Drag reduction phenomenon in pipelines has received lots of attention during the past decades due to its potential engineering applications, especially in fluid transporting industries. Various methods to enhance drag reduction have been developed throughout the years and divided into two categories;non-additives method and additives method. Both categories have different types of methods, with different formulations and applications which will generally be discussed in this review. Among all the methods discussed, drag reduction using polymer additive is as one of the most enticing and desirable methods. It has been the subject of research in this field and has been studied extensively for quite some time. It is due to its ability to reduce drag up to 80% when added in minute concentrations. Reducing drag in the pipe will require less pumping power thus offering economic relieves to the industries. So, this paper will be focusing more on the use of polymer additives as drag reducing agent, the general formulations of the additives, major issues involving the use of drag reducing polymers, and the potential applications of it. However, despite the extensive works of drag reduction polymer, there are still no models that accurately explain the mechanism of drag reduction. More studies needed to be done to have a better understanding of the phenomenon. Therefore, future research areas and potential approaches are proposed for future work.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 51076036 and 51206033)the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (Grant No.51121004)+2 种基金the Fundamental Research Funds for the Central Universities,China (Grant No. HIT.BRET2.2010008)the Doctoral Fund of Ministry of Education of China (Grant No. 20112302110020)the China Postdoctoral Science Foundation (Grant No. 2011M500652)
文摘Direct numerical simulations （DNS） were performed for the forced homogeneous isotropic turbulence （FHIT） with/without polymer additives in order to elaborate the characteristics of the turbulent energy cascading influenced by drag-reducing effects. The finite elastic non-linear extensibility-Peterlin model （FENE-P） was used as the conformation tensor equation for the viscoelastic polymer solution. Detailed analyses of DNS data were carried out in this paper for the turbulence scaling law and the topological dynamics of FHIT as well as the important turbulent parameters, including turbulent kinetic energy spectra, enstrophy and strain, velocity structure function, small-scale intermittency, etc. A natural and straightforward definition for the drag reduction rate was also proposed for the drag-reducing FHIT based on the decrease degree of the turbulent kinetic energy. It was found that the turbulent energy cascading in the FHIT was greatly modified by the drag-reducing polymer additives. The enstrophy and the strain fields in the FH1T of the polymer solution were remarkably weakened as compared with their Newtonian counterparts. The small-scale vortices and the small-scale intermittency were all inhibited by the viscoelastic effects in the FHIT of the polymer solution. However, the scaling law in a fashion of extended self-similarity for the FHIT of the polymer solution, within the presently simulated range of Weissenberg numbers, had no distinct differences compared with that of the Newtonian fluid case.
文摘In this work, a rheological study of automotive lubricant oils, neutral light paraffinic (NLP) and neutral medium paraffinic (NMP), additivated with two commercial viscosity index improvers-VIIs, based on hydrogenated poly (isoprene-co-styrene), at different concentrations, was carried out. The study included the determination of the kinematic viscosity of the mixtures, the calculation of the viscosity indexes and their behavior when subjected to various rheometric experiments, including stress sweep, steady state flow, creep and recovery, and temperature ramp oscillatory tests. The obtained results showed the efficacy of the additives as viscosity index improvers, enabling a significant increase in the viscosity index of the pure oils at relatively low concentrations. The determination of the storage (G’) and of the loss (G”) moduli for the mixtures oil/VII additives showed a large predominance of the viscous effect over the elastic one. Except when under low shear stress, the mixtures showed a pseudoplastic behavior, with the flow curves being adjusted to fit the Ostwald-de-Waele model (Power Law), with negative flow behavior indexes.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51206033 and 51276046)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20112302110020)+2 种基金the China Postdoctoral Science Foundation(Grant No.2011M500652)the Heilongjiang Postdoctoral Science Foundation,China(Grant No.2011LBH-Z11139)the Natural Scientific Research Innovation Foundation in Harbin Institute of Technology,China(Grant No.HIT.NSRIF.2012070)
文摘Large-eddy simulations （LES） based on the temporal approximate deconvolution model were performed for a forced homogeneous isotropic turbulence （FHIT） with polymer additives at moderate Taylor Reynolds number. Finitely extensible nonlinear elastic in the Peterlin approximation model was adopted as the constitutive equation for the filtered conformation tensor of the polymer molecules. The LES results were verified through comparisons with the direct numerical simulation results. Using the LES database of the FHIT in the Newtonian fluid and the polymer solution flows, the polymer effects on some important parameters such as strain, vorticity, drag reduction, and so forth were studied. By extracting the vortex structures and exploring the flatness factor through a high-order correlation function of velocity derivative and wavelet analysis, it can be found that the small-scale vortex structures and small-scale intermittency in the FHIT are all inhibited due to the existence of the polymers. The extended self-similarity scaling law in the polymer solution flow shows no apparent difference from that in the Newtonian fluid flow at the currently simulated ranges of Reynolds and Weissenberg numbers.
