Flow Analysis and Structural Design of Penstock Bifurcation of Kulekhani III HEP
Flow Analysis and Structural Design of Penstock Bifurcation of Kulekhani III HEP
Flow Analysis and Structural Design of Penstock Bifurcation of Kulekhani III HEP
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Flow Analysis and Structural Design of Penstock Bifurcation of Kulekhani III HEP
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Abstract
The development of hydropower is possible with the development of sound knowledge about all aspects. Various
guidelines are available for the design of hydropower plants which are based on experience and theoretical basis.
With the development of modern techniques and availability of enhance computational devices, various problems
can be solved using these techniques. One of these areas is the design optimization of penstock manifold and
bifurcation. With the proper design of penstock bifurcation, the head loss incurring in the mixed flow condition can
be minimized the output from both the units can be maximized. The conventional technique of design based on
codes results in high thickness and overall increase in material quantity. The structural design can be optimized
using Finite Element Method by accurately determining the three dimensional stress condition. Application of
Computational Fluid Dynamics and Finite element analysis in the field of hydropower projects is the current
industrial practice. However, it has found very limited use in context of Nepal. The research aims to enhance the
theoretical knowledge base for the application of Computational Fluid Dynamics and Finite Element Method for
the design and analysis of penstock bifurcation. The manifold arrangement of Kulekhani-III Hydropower Project
was chosen for the optimization. The proposed manifold arrangement was modelled and flow analysis was
performed. The flow and head loss were reviewed and the manifold arrangement was revised successively to
achieve acceptable geometry. The bifurcation was given thickness and reinforcements and the solid model for the
same was prepared which was then subjected to Finite Element Analysis. The result of stress and deformation
was observed and checked against prevailing design codes. Finally the acceptable design of bifurcation was
recommended for fabrication and installation.
Keywords
Computational Fluid Dynamics, Bifurcation, Finite Element Analysis
1. Introduction huge. Hence, most of the plant will have at least two
generating units. In many cases the number of units are
Penstock is the pressure conduit between the turbine optimized based on the transportation limitation.So
inlet valve and the first open water upstream from the when there are more than one generating units, each one
turbine. The open water can be a surge tank, forebay or of them will be required to be feed up by penstock.
a reservoir. The penstock is mostly made up of welded
carbon steel. In some low head applications, HDPE Unless the head is very low, it is not economical to use
pipes are used for this purpose. Penstocks should be separate penstock for each units. So mostly a single
optimized with respect to the head loss and the material penstock will carry water from free water surface near
requirement.In the hydropower plant, a single the powerhouse. Then it will be branched depending
generating unit is seldom chosen. The turbines and upon the number of units. When there is two generating
generators needs periodic repair and maintenance. The units, the penstock is branched into two segments. This
shut down time required for maintenance purpose is the branching is called penstock bifurcation.
time the generation will be lost. In case of single unit, The profile of the manifolds affects the loss in the
the plant generation loss for the maintenance will be available water head significantly. This loss can
Flow Analysis and Structural Design of Penstock Bifurcation of Kulekhani III HEP
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Proceedings of IOE Graduate Conference, 2016
been examined and had been assumed which is fair for slightly high [?](E.Mosonyi, 1991). As there are plenty
such flow condition [3]. High resolution solver option of space available in the penstock alignment, the
with convergence criteria of 10e-4 shall be selected. bifurcation is purposed to be shifted towards upstream
side in order to reduce the branching angle to 30
The selected geometry will be recommended for
degrees. It is well known to us (E.Mosonyi, 1991) that
structural design. Analysis of bifurcation geometry
this will improve the flow behavior significantly. The
needs to be carried out in order to check its structural
requirement of increased structural strength will be well
capacity to withstand the given loading condition. This
justified by the savings in the head loss and
can be performed using conventional analytical method.
improvement of flow behavior.
However, due to the complicated geometry of the
bifurcation, this method does not yields accurate result.
So, to optimize the design works, finite element method
needs to be employed to calculate the structural stress of
the bifurcation in the given condition.Following
methodology shall be employed for structural analysis:
3. Flow Analysis
Figure 4: Velocity Distribution at Mid Plane
Option 1 is the option initially purposed by the project.
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Flow Analysis and Structural Design of Penstock Bifurcation of Kulekhani III HEP
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Proceedings of IOE Graduate Conference, 2016
4. Structural Analysis
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Flow Analysis and Structural Design of Penstock Bifurcation of Kulekhani III HEP
Acknowledgments
References
[1] S. Ahmad. Head loss in symmetric bifurcation. Master’s
Figure 13: Bifurcation installed at site thesis, UNIVERSITY OF BRITISH COLUMBIA, 1943.
[2] R. G. C. A. AGUIRRE. Head losses anslysis in
symmetrical trifurcation of penstock-high pressure
5. Conclusion pipeline systems cfd. IGHEM, 2016.
It was observed that the loss coefficient for bifurcation [3] Ansys Inc. Ansys cfx theory guide. IGHEM, 2016.
has reduced from 0.44 to 0.21. This will add up in the [4] E.Mosoniya. High Head Power Plant Volume IIA and
overall plant performance in long term. Furthermore, IIB. AKADIMIA KIADO, Bdapest, 1991.
with the help of Finite Element Analysis, we are sure [5] ASME. Boiler and Pressure Vessel Code. ASME, 2004.
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