A common method to calculate the flow rate and consequently hydraulic efficiency in hydropower plants is the pressure-time method. In the present work, the pressure-time method is studied numerically by three-dimensional (3D) simulations and considering the change in the pipe cross section (a contraction). Four different contraction angles are selected for the investigations. The unsteady Reynolds-averaged Navier–Stokes (URANS) equations and the low-Reynolds k–ω shear stress transport (SST) turbulence model are used to simulate the turbulent flow. The flow physics in the presence of the contraction, and during the deceleration period, is studied. The flow rate is calculated considering all the losses: wall shear stress, normal stresses, and also flux of momentum in the flow. The importance of each term is evaluated showing that the flux of momentum plays a most important role in the flow rate estimation while the viscous losses term is the second important factor. To extend the viscous losses calculations applicability to real systems, the quasi-steady friction approach is employed. The results showed that considering all the losses, the increase in the contraction angle does not influence the calculated errors significantly. However, the use of the quasi-steady friction factor introduces a larger error, and the results are reliable approximately up to a contraction angle of ϴ = 10 deg. The reason imparts to the formation of a local recirculation zone upstream and inside the contraction, which appears earlier as the contraction angle increases. This feature cannot be captured by the quasi-steady friction models, which are derived based on the fully developed flow assumption.
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October 2018
Research-Article
Numerical Investigation of the Pressure-Time Method Considering Pipe With Variable Cross Section
Simindokht Saemi,
Simindokht Saemi
School of Mechanical Engineering,
College of Engineering,
University of Tehran,
Tehran 1439955961, Iran;
College of Engineering,
University of Tehran,
Tehran 1439955961, Iran;
Division of Fluid and Experimental Mechanics,
Lulea University of Technology,
Lulea SE 971 87, Sweden
e-mail: si.saemi@ut.ac.ir
Lulea University of Technology,
Lulea SE 971 87, Sweden
e-mail: si.saemi@ut.ac.ir
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Mehrdad Raisee,
Mehrdad Raisee
Associate Professor
Hydraulic Machinery Research Institute,
School of Mechanical Engineering,
College of Engineering,
University of Tehran,
Tehran 1439955961, Iran
e-mail: mraisee@ut.ac.ir
Hydraulic Machinery Research Institute,
School of Mechanical Engineering,
College of Engineering,
University of Tehran,
Tehran 1439955961, Iran
e-mail: mraisee@ut.ac.ir
Search for other works by this author on:
Michel J. Cervantes,
Michel J. Cervantes
Professor
Division of Fluid and
Experimental Mechanics,
Lulea University of Technology,
Lulea SE 971 87, Sweden
e-mail: Michel.Cervantes@ltu.se
Division of Fluid and
Experimental Mechanics,
Lulea University of Technology,
Lulea SE 971 87, Sweden
e-mail: Michel.Cervantes@ltu.se
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Ahmad Nourbakhsh
Ahmad Nourbakhsh
Professor
Hydraulic Machinery Research Institute,
School of Mechanical Engineering,
College of Engineering,
University of Tehran,
Tehran 1439955961, Iran
e-mail: anour@ut.ac.ir
Hydraulic Machinery Research Institute,
School of Mechanical Engineering,
College of Engineering,
University of Tehran,
Tehran 1439955961, Iran
e-mail: anour@ut.ac.ir
Search for other works by this author on:
Simindokht Saemi
School of Mechanical Engineering,
College of Engineering,
University of Tehran,
Tehran 1439955961, Iran;
College of Engineering,
University of Tehran,
Tehran 1439955961, Iran;
Division of Fluid and Experimental Mechanics,
Lulea University of Technology,
Lulea SE 971 87, Sweden
e-mail: si.saemi@ut.ac.ir
Lulea University of Technology,
Lulea SE 971 87, Sweden
e-mail: si.saemi@ut.ac.ir
Mehrdad Raisee
Associate Professor
Hydraulic Machinery Research Institute,
School of Mechanical Engineering,
College of Engineering,
University of Tehran,
Tehran 1439955961, Iran
e-mail: mraisee@ut.ac.ir
Hydraulic Machinery Research Institute,
School of Mechanical Engineering,
College of Engineering,
University of Tehran,
Tehran 1439955961, Iran
e-mail: mraisee@ut.ac.ir
Michel J. Cervantes
Professor
Division of Fluid and
Experimental Mechanics,
Lulea University of Technology,
Lulea SE 971 87, Sweden
e-mail: Michel.Cervantes@ltu.se
Division of Fluid and
Experimental Mechanics,
Lulea University of Technology,
Lulea SE 971 87, Sweden
e-mail: Michel.Cervantes@ltu.se
Ahmad Nourbakhsh
Professor
Hydraulic Machinery Research Institute,
School of Mechanical Engineering,
College of Engineering,
University of Tehran,
Tehran 1439955961, Iran
e-mail: anour@ut.ac.ir
Hydraulic Machinery Research Institute,
School of Mechanical Engineering,
College of Engineering,
University of Tehran,
Tehran 1439955961, Iran
e-mail: anour@ut.ac.ir
1Corresponding author.
Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received April 26, 2018; final manuscript received June 26, 2018; published online August 6, 2018. Assoc. Editor: Ioannis K. Nikolos.
J. Fluids Eng. Oct 2018, 140(10): 101401 (15 pages)
Published Online: August 6, 2018
Article history
Received:
April 26, 2018
Revised:
June 26, 2018
Citation
Saemi, S., Raisee, M., Cervantes, M. J., and Nourbakhsh, A. (August 6, 2018). "Numerical Investigation of the Pressure-Time Method Considering Pipe With Variable Cross Section." ASME. J. Fluids Eng. October 2018; 140(10): 101401. https://doi.org/10.1115/1.4040718
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