论文标题
具有柔性和刚性聚合物溶液的湍流管流的统计和光谱分析
Statistics and spectral analysis of turbulent duct flows with flexible and rigid polymer solutions
论文作者
论文摘要
我们提出了对湍流拖动减少的实验研究，并具有柔性和刚性聚合物溶液。柔性聚合物是部分水解聚丙烯酰胺（HPAM），刚性聚合物是Xanthan Gum（XG）。实验是以低阻力减少（$ \％DR <40 $），高阻力减少（$ \％DR> 40 $）和最大拖动减少（其中的速度配置文件$ u^+$大致与维尔克的渐近线匹配）。我们比较了通过激光多普勒驱动器（LDA）测量的流速速度波动的速度曲线，流向和壁正常雷诺的应力和功率谱。我们的结果表明，XG和HPAM聚合物对湍流的影响相似，前提是Reynolds数字和$ \％DR $也相似。在高水平的$ \％DR $下，XG和HPAM流的流速速度波动的功率谱密度显示，惯性范围内的幂律衰减接近$ -3 $而不是$ -5/3 $。最近将$ -3 $的功率光谱坡度解释为聚合物喷气机中弹性惯性湍流（EIT）的证据。在相对较低的浓度下，我们观察到柔性聚合物溶液在减少阻力方面更有效，而XG仅以很高的浓度达到MDR。因此，我们假设具有较高浓度的聚合物聚集体的形成有助于增加粘弹性，从而在XG和其他刚性聚合物溶液中形成$ \％DR $。
We present an experimental investigation of turbulent drag reduction with flexible and rigid polymer solutions. The flexible polymer is partially hydrolyzed polyacrylamide (HPAM) and the rigid polymer is xanthan gum (XG). The experiments are carried out at low drag reduction ($\%DR < 40$), high drag reduction ($\%DR > 40$) and maximum drag reduction (where the velocity profile $U^+$ roughly matches Virk's asymptote). We compare velocity profiles, streamwise and wall-normal Reynolds stresses and power spectra of streamwise velocity fluctuations measured by Laser Doppler Anemometry (LDA). Our results show that the effects of both XG and HPAM polymers on turbulence are similar, provided that the Reynolds numbers and $\%DR$ are also similar. At high levels of $\%DR$, the power spectral densities of streamwise velocity fluctuations of both XG and HPAM flows show a power-law decay near $-3$ instead of $-5/3$ in the inertial range. A slope of the power spectra of $-3$ was recently interpreted as evidence of elasto-inertial turbulence (EIT) in polymer jets. At relatively low concentrations, we observe that flexible polymer solutions are more effective at reducing drag, while XG only reaches MDR at very high concentrations. Thus, we hypothesize that the formation of polymer aggregates with higher concentrations contributes to increase viscoelasticity, and thus $\%DR$, with XG and other rigid polymer solutions.
