دانلود رایگان مقاله انگلیسی تحلیل عددی شناسایی افت فشار در فشار بالای سه انشعابی در دستگاه انرژی آبی - الزویر 2019

Abstract.

Many different types of branching have been developed, such as bifurcation, trifurcation, and manifolds, among others. These configurations are used in penstocks to transport water from surge tanks to power houses in order to feed several turbines at the same time. This arrangement allows for smaller assembly costs in comparison with independent penstock systems. Nevertheless, such installations can generate higher head losses in the system in comparison with single systems. This study focuses on the quantification of these head losses as a function of volumetric flow rate using Computational Fluid Dynamics (CFD) and later validated with previously published results. To determine the coefficient of head losses three mesh settings were analyzed: hexahedral, tetrahedral and hybrid, for both a steady state and transitory flow. Based on the literature, the k-ω turbulence model was used, with refinement to elements near the wall to check y+. To the simulation transitory, the SAS model was used for analysis of the instability in the trifurcation.

4. Conclusions

The trifurcation employment has particular characteristics for each project, resulting in different geometries, even when all of them perform the same function. When the values of the diameter ratio, pressure or flow are different, the loss coefficients and the flow variations can have major differences in the results. Therefore, a strict validation of the numerical results of the trifurcation of Gurara - ALSTOM® can only be performed with a reduced model of experimental data. However, the approach based on CFD, carefully carried out, based on good mesh analysis, can be an appropriate choice of turbulence models, boundary conditions and other parameters, where the numerical and theoretical analyses should be strongly based on the literature and on own experience of the research group. The results from the numerical analysis of the Gurara-Nigeria project is calculated at the operating point and beyond in order to have a wide range of results for one later comparison with other numerical and experimental results of pressure losses. However, many results (experimental and numerical) are only calculated at the design point. On the other hand, in order to generalize the results for the particular conditions of each trifurcation, the loss coefficient correlates with the Reynolds number for the steady state, and for the non-stationary state, comparisons were made according to the variation in the total loss coefficient at the time, by the flow. There is very little information related to the loss coefficients in trifurcations in transient flow. In specialized literature two studies are found that report the experimental and numerical results about the behavior of pressure loss: Ruprechs et al [10] and Tate et al [9]. For the results obtained by Ruprechs considering one spherical trifurcation, the experimental data were obtained based on a smaller scale model with an acquisition time of 210 s, as seen in Figure 15.