Fig. 7. Validation case, a = 90_. Normalized mean bulk concentration (top) and normalized mean volumetric flow (bottom) as a function of rQ at both outlets. _ outlet2 and _ outlet1 experimental data. —– 2D numerical simulation, _____ 3D numerical simulation.
The Q profiles show a similar behavior to the C profiles. However, the critical point found here, where volumetric flows at both outlets are the same, is displaced to rQ = 1.0, since both pipes transport the same fluid with equal volumetric flow. Analyzing the passive scalar profiles, it may be concluded that most of the fluid evacuated by outlet2 came through inlet1 (more than 70%) and vice versa.
The pressure losses, defined as DP = (Pinlet _ Poutlet)/Pinlet, as a function of rQ, are illustrated in Fig. 8. The difference between both numerical configurations is comparable with measurement errors in experimental data, lower than 4%. Higher differences are mainly found for the highest rQ values studied. The two dimension approximation proved to be a good way to save computational resources for this kind of study, which requires a high number of numerical data. Just for the validation case, more than 50 simulations were performed. The major discrepancies between numerical and experimental data were found to be lower than 4% in terms of scalar concentration, which establishes the numerical model accuracy.
5. Influence of the junction angle a
As a consequence of the good performance of the numerical model shown in the previous section, the study of configurations with different a angles was achieved considering four other angles: a = 45_, 67.5_, 112.5_ and 135_. Flow conditions and number of grid points were similar for every case. Only an increase of _5% in the
Fig. 8. Validation case, a = 90_. Mean pressure loss as a function of rQ at both pipes. _ outlet2 and _ outlet1 experimental data. —– 2D numerical simulation, _____ 3D numerical simulation.
grid resolution at the junction was necessary for cases a = 45_ and 135_. The whole range of rQ values studied for a = 90_ was not possible for every angle. For a = 135_, convergence was not attained for low and high rQ values. Many other authors have also reported convergence problems in flows with more than one exit [3], due to mass conservation convergence.
The normalized bulk volumetric flow and passive scalar concentration profiles are shown in Figs. 9 and 10 (a = 90_ included) as a function of rQ. The critical point in the bulk volumetric flow profiles takes place at rQ = 1.0 for every case, although they present profiles with different slopes. The curves with maximum and minimum slope are cases a = 45_ and 135_, respectively.
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