Numerical simulations and investigation of a method for controlling the vortex rope formation in draft tubes are carried out in this paper, which is the second part of a two-paper series. As shown in the companion paper, formation of the vortex rope is associated with a large stagnant region at the center of the draft tube. Therefore, it is concluded that a successful control technique should focus on the elimination of this region. In practice, this can be performed by axially injecting a small fraction (a few percent of the total flow rate) of water into the draft tube. Water jet is supplied from the high-pressure flow upstream of the turbine spiral case by a bypass line; thus, no extra pump is needed in this method. It is shown that this method is very effective in elimination of the stagnant region in a simplified draft tube operating at two part-load conditions, i.e., at 91% and 70% of the best efficiency point (BEP) flow rate. This results in improvement of the draft tube performance and reduction of hydraulic losses. The loss coefficient is reduced by as much as 50% for the case with 91% of BEP flow rate and 14% for the case with 70% of BEP flow rate. Unsteady, three-dimensional simulations show that the jet increases the axial momentum of flow at the center of the draft tube and decreases the wake of the crown cone and thereby decreases the shear at the interface of the stagnant region and high velocity outer flow, which ultimately results in elimination of the vortex rope. Furthermore, reduction (by about 1/3 in the case with 70% of BEP flow rate) of strong pressure fluctuations leads to reliable operation of the turbine.
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June 2014
Research-Article
Flow in the Simplified Draft Tube of a Francis Turbine Operating at Partial Load—Part II: Control of the Vortex Rope
Hosein Foroutan,
Hosein Foroutan
1
Department of Mechanical and
Nuclear Engineering,
e-mail: hosein@psu.edu
Nuclear Engineering,
The Pennsylvania State University
,338C Reber Building
,University Park, PA 16802
e-mail: hosein@psu.edu
1Corresponding author.
Search for other works by this author on:
Savas Yavuzkurt
Savas Yavuzkurt
Department of Mechanical and
Nuclear Engineering,
e-mail: sqy@psu.edu
Nuclear Engineering,
The Pennsylvania State University
,327 Reber Building
,University Park, PA 16802
e-mail: sqy@psu.edu
Search for other works by this author on:
Hosein Foroutan
Department of Mechanical and
Nuclear Engineering,
e-mail: hosein@psu.edu
Nuclear Engineering,
The Pennsylvania State University
,338C Reber Building
,University Park, PA 16802
e-mail: hosein@psu.edu
Savas Yavuzkurt
Department of Mechanical and
Nuclear Engineering,
e-mail: sqy@psu.edu
Nuclear Engineering,
The Pennsylvania State University
,327 Reber Building
,University Park, PA 16802
e-mail: sqy@psu.edu
1Corresponding author.
Manuscript received October 6, 2013; final manuscript received February 7, 2014; accepted manuscript posted February 12, 2014; published online March 6, 2014. Assoc. Editor: Kenji Takizawa.
J. Appl. Mech. Jun 2014, 81(6): 061011 (7 pages)
Published Online: March 6, 2014
Article history
Received:
October 6, 2013
Revision Received:
February 7, 2014
Accepted:
February 12, 2014
Citation
Foroutan, H., and Yavuzkurt, S. (March 6, 2014). "Flow in the Simplified Draft Tube of a Francis Turbine Operating at Partial Load—Part II: Control of the Vortex Rope." ASME. J. Appl. Mech. June 2014; 81(6): 061011. https://doi.org/10.1115/1.4026818
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