Turbulent flows of viscoplastic fluids at high Reynolds numbers have been investigated recently with direct numerical simulations (DNS) but experimental results have been limited. For this reason, we carry out an experimental study of fully turbulent flows of a yield stress fluid in a rectangular duct with a high-resolution laser doppler anemometry (LDA) setup. We employ aqueous Carbopol solutions, often considered to be a simple yield stress fluid. We formulate different concentrations to address the effect of the rheology of the fluid on the turbulence statistics at an approximately constant Reynolds number. Additionally, we also perform experiments with a single Carbopol formulation at different Reynolds numbers to study its effect. The flow analysis is performed via rheology measurements, turbulence statistics and power spectral densities of velocity fluctuations. The addition of Carbopol to the flow increases turbulence anisotropy, with an enhancement of streamwise velocity fluctuations and a decrease in wall normal velocity fluctuations in comparison to water at the same mean velocity. This change is reflected on the power spectral densities of streamwise velocity fluctuations, where we observe a large increase in energy of large scale turbulent structures. Conversely, the energy of smaller scales is decreased in comparison to water, where the energy drops with a steeper scale than the Newtonian power law of $k_x^{-5∕3}$. As we increase the Reynolds number with a Carbopol solution, the streamwise Reynolds stresses approach Newtonian values in the core, which suggests diminishing effects of shear-thinning. The power spectral densities reveal that the energy content at larger scales decreases slightly with the Reynolds number. However, the shear-thinning effects do not disappear even as the Reynolds number approaches 50,000.

最近使用直接数值模拟 (DNS) 研究了高雷诺数下粘塑性流体的湍流，但实验结果有限。因此，我们使用高分辨率激光多普勒风速仪 (LDA) 装置对矩形管道中屈服应力流体的完全湍流进行了实验研究。我们使用 Carbopol 水溶液，通常被认为是一种简单的屈服应力流体。我们制定了不同的浓度，以解决流体流变学对近似恒定雷诺数下的湍流统计的影响。此外，我们还使用不同雷诺数的单一 Carbopol 配方进行实验，以研究其效果。流动分析是通过流变学测量进行的，湍流统计和速度波动的功率谱密度。与相同平均速度下的水相比，将 Carbopol 添加到流动中会增加湍流各向异性，同时增强流向速度波动并减少壁面法向速度波动。这种变化反映在流向速度波动的功率谱密度上，我们观察到大规模湍流结构的能量大幅增加。相反，与水相比，较小尺度的能量减少，其中能量以比牛顿幂定律更陡峭的尺度下降 与相同平均速度下的水相比，流向速度波动的增强和壁面法向速度波动的减少。这种变化反映在流向速度波动的功率谱密度上，我们观察到大规模湍流结构的能量大幅增加。相反，与水相比，较小尺度的能量减少，其中能量以比牛顿幂定律更陡峭的尺度下降 与相同平均速度的水相比，流向速度波动的增强和壁面法向速度波动的减少。这种变化反映在流向速度波动的功率谱密度上，我们观察到大规模湍流结构的能量大幅增加。相反，与水相比，较小尺度的能量减少，其中能量以比牛顿幂定律更陡峭的尺度下降${克}_X^{-5∕3}$. 当我们使用 Carbopol 溶液增加雷诺数时，流向雷诺应力接近核心中的牛顿值，这表明剪切稀化的影响正在减弱。功率谱密度表明，较大尺度的能量含量随着雷诺数的增加而略有下降。然而，即使雷诺数接近 50,000，剪切稀化效应也不会消失。