Energy Loss Analysis of 3D Asymmetric Trifurcations Using CFD
Abstract
Head losses are very common in penstock trifurcations. In this paper, six cases of 3D asymmetric trifurcations have been modeled with main pipe length & diameter of 1.3716m & 0.0254m, respectively and branch pipe lengths & diameters of 0.762m & 0.0196m, respectively. Volumetric flow rates, velocity magnitudes, dynamic and total pressure contours and their values have been computed. Energy loss coefficients have been computed for branch pipes for an input air velocity of 3m/s by pressure data obtained from the CFD analysis. The maximum values of velocity magnitude, dynamic and total pressures are observed in the branch-2 and head losses in branch-2 are relatively less.
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Introduction
In penstocks used for hydropower projects, trifurcations along with the other components, help in producing electricity. These trifurcations supplement water supply to multiple turbines at the same time. Despite having the economical advantage over independent systems, even this system is not free from losses. The comparison of velocity magnitudes, dynamic and total pressure contours and determination of head loss coefficients in the branch pipes sums up the interest of this study.
Conclusion
Energy (head) loss analysis has been carried out and volumetric flow rates, velocity magnitudes, and dynamic & total pressures have been determined for all the six cases of asymmetric trifurcations. It is seen that the fluid flow rate, velocity magnitude and dynamic & total pressures are more in the branch-2 compared to the other two branches. Smaller values of head losses have been obtained for branch-2 in all the cases. This is because there is only change in the pipe area and more energy dissipation that is taking place is because of the viscous friction at the wall, while the side branches suffer a directional flow change (secondary flow) along with the cross-sectional variation [1]. The turbulence at pipe trifurcation junction, angle of trifurcation, and diameter ratio are mainly responsible for the losses and separation of flow [4].