In this paper, we present result from a direct numerical simulation (DNS) of turbulent flow in a converging T-junction for both Newtonian (water) and non-Newtonian inelastic fluid (dilute Xanthan Gum solution). Based on experimental data, the Bird-Carreau law is used to capture the inelastic shear thinning property of the solution. For the Xanthan solution, the viscosity at rest is about 100 times greater than the viscosity at high shear-rate. A passive scalar is introduced in the transverse branch to investigate the mixing in such configuration. The nominal Reynolds number at the exit varies from 4800 to 8000 for the Newtonian cases and for the same inflow rates, the non-Newtonian flow will be necessarily at lower nominal Reynolds number. Two regimes are explored as a function of the inlet velocity ratio $r=U_b/U_m$ : the ”deflecting” regime noted DR ($r=1$) and the ”impinging” regime noted IR ($r=4$). For the non-Newtonian cases, two viscous cores are observed before the junction. After the junction a laminar state is obtained for the lower flow rate conditions. Surprisingly, in spite of a large viscosity at rest, a self-sustained non-Newtonian turbulence is achieved except for one case. We describe existing vortex mechanisms which pilot the scalar mixing. In addition, we show that in the non-Newtonian cases, the existing peak of turbulence is only shifted in the DR case. The shift is probably due to the nature of the fluid and not to the dynamical regime. After an intense turbulent zone, we show that a re-laminarization zone appears in the non-Newtonian case which reduces the fluctuation as well as mixing. As a result, IR has a better mixing quality than DR.

在本文中，我们从牛顿（水）和非牛顿非弹性流体（稀黄原胶溶液）的收敛T形结中湍流的直接数值模拟（DNS）中得出结果。基于实验数据，Bird-Carreau定律用于捕获溶液的非弹性剪切稀化特性。对于黄原胶溶液，静止时的粘度是高剪切速率下的粘度的约100倍。在横向分支中引入无源标量以研究这种配置下的混合。对于牛顿情况，出口处的标称雷诺数在4800到8000之间变化，并且对于相同的流入速率，非牛顿流量必然在较低的标称雷诺数下。根据入口速度比探索了两种状态$\mathrm{[R}={ü}_b/{ü}_{米}$ ：DR的“偏斜”制度（$\mathrm{[R}=\mathrm{1个}$）和“影响”制度中提到的IR（$\mathrm{[R}=4$）。对于非牛顿的情况，在连接之前观察到两个粘性核心。连接后，在较低的流速条件下会获得层流状态。出乎意料的是，尽管在静止时粘度很大，但除了一种情况外，仍可实现自持的非牛顿湍流。我们描述了控制标量混合的现有涡旋机制。此外，我们表明，在非牛顿情况下，仅湍流存在的湍流峰值仅在DR情况下发生偏移。这种变化可能是由于流体的性质引起的，而不是由于动态状态引起的。经过强烈的湍流区后，我们表明在非牛顿的情况下出现了再分层区，这减少了波动以及混合。结果，IR具有比DR更好的混合质量。