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Direct numerical simulation study of the interaction between the polymer effect and velocity gradient tensor in decaying homogeneous isotropic turbulence 下载免费PDF全文
Direct numerical simulation of decaying homogeneous isotropic turbulence (DHIT) of a polymer solution is performed. In order to understand the polymer effect on turbulence or additive-turbulence interaction, we directly investigate the influence of polymers on velocity gradient tensor including vorticity and strain. By visualizing vortex tubes and sheets, we observe a remarkable inhibition of vortex structures in an intermediate-scale field and a small-scale field but not for a large scale field in DHIT with polymers. The geometric study indicates a strong relevance among the vorticity vector, rate-of-strain tensor, and polymer conformation tensor. Joint probability density functions show that the polymer effect can increase "strain generation resistance" and "vorticity generation resistance", i.e., inhibit the generation of vortex sheets and tubes, ultimately leading to turbulence inhibition effects. 相似文献
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Influence of polymer additives on turbulent energy cascading in forced homogeneous isotropic turbulence studied by direct numerical simulations 下载免费PDF全文
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 FHIT 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. 相似文献
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Large-eddy simulations of a forced homogeneous isotropic turbulence with polymer additives 下载免费PDF全文
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. 相似文献
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黏弹性流体纯弹性不稳定现象研究综述 总被引:1,自引:0,他引:1
近年来黏弹性流体流动的纯弹性不稳定现象引起了越来越多学者的关注与研究,与牛顿流体惯性不稳定现象不同,这种现象是由黏弹性流体流动中的弹性应力和黏性力之间相互作用,使得在较低的雷诺数Re下即可产生复杂的流动分岔不稳定现象.当流动中的弹性数较大时,在ReRec(惯性不稳定性产生的临界雷诺数)下,黏弹性流体流动中也可能产生完全由弹性应力引起的纯弹性不稳定现象.以Taylor–Couette流动为基础,对黏弹性流体流动中产生纯弹性不稳定现象的研究现状从实验、理论分析和数值模拟3个方面进行总结.通过对比这3个方面,总结了弹性流动不稳定现象发生的过程与机理、流动不稳定性产生的影响因素及其作用方式,并对目前研究的不足之处以及今后可能的发展趋势作了分析和展望. 相似文献
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