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Research Papers: Multiphase Flows

Investigation on Combined Air and Water Injection in Francis Turbine Draft Tube to Reduce Vortex Rope Effects

[+] Author and Article Information
Moona Mohammadi

Mechanical Engineering Department,
Shahid Chamran University of Ahvaz,
Ahvaz 65155, Iran
e-mail: moona_mohammadi@yahoo.com

Ebrahim Hajidavalloo

Mechanical Engineering Department,
Shahid Chamran University of Ahvaz,
Ahvaz 61355, Iran
e-mail: hajidae@scu.ac.ir

Morteza Behbahani-Nejad

Mechanical Engineering Department,
Shahid Chamran University of Ahvaz,
Ahvaz 61355, Iran
e-mail: bnmorteza@scu.ac.ir

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received April 4, 2018; final manuscript received September 23, 2018; published online November 16, 2018. Assoc. Editor: Riccardo Mereu.

J. Fluids Eng 141(5), 051301 (Nov 16, 2018) (12 pages) Paper No: FE-18-1195; doi: 10.1115/1.4041565 History: Received April 04, 2018; Revised September 23, 2018

In this paper, the effect of water, air, and their combined injection from two different injection points is studied in order to reduce vorticity effects in a draft tube of prototype turbine working at three operating points. The flow from spiral case to the end of draft tube is simulated using the shear stress transport k–ω turbulence and two-phase models. Using an appropriate validation method, acceptable results were obtained under the noninjection condition. To determine suitable number of points and inlet flow rate for air injection as well as the appropriate nozzle diameter for air and water injection, a new method which considers the ratio of total loss to the pressure recovery factor is used, in addition to using the traditional method which calculates the total loss in the draft tube. Comparing results of the three types of injections shows air injection in the operating range greater than 70% of turbine design flow rate, is much more effective than water injection or the combination of air and water injection. However, in the operating range below 70%, either water or air injections are not suitable, but combination of these two fluids can improve system performance.

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References

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Figures

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Fig. 3

Schematic of a turbine and locations of air and water injection points

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Fig. 2

Geometry of the Maroon power plant from the stay vanes to the end of draft tube

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Fig. 1

Geometry of the Maroon power plant from the spiral case to the end of draft tube

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Fig. 4

Side view of the studied geometry

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Fig. 5

Comparison of simulation and experimental results for (a) axial velocity and (b) circumferential velocity, in EPFL draft tube model, using various turbulence models in 158 mm distance from inlet computational domain

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Fig. 6

Comparison of simulation and experimental results for (a) axial velocity and (b) turbulence kinetic energy, in EPFL draft tube model, using various discretization schemes in 158 mm distance from inlet computational domain

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Fig. 11

Loss and loss to pressure recovery factor ratio versus airflow rate for various nozzle diameters at 66.6% operating point

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Fig. 12

Loss and loss to pressure recovery factor ratio versus airflow rate at three operating points for 1 cm nozzle diameter, only air injection

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Fig. 9

Total loss and ratio of total loss to pressure recovery factor versus nozzle diameter for three operating points for water injection

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Fig. 10

Loss and ratio of loss to pressure recovery factor versus nozzle diameter at 0.5% of the airflow rate at 66.6% operating point

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Fig. 8

Method of obtaining three unknowns for air injection

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Fig. 7

Determining the appropriate nozzle diameter in air and water injection, using two methods

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Fig. 13

Total loss and total loss to pressure recovery factor ratio versus airflow rates at three operating points in combined air and water injection condition for 1 cm nozzle diameter

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Fig. 14

Comparison between air injection and combined air and water injection at 100% operating point for 1 cm nozzle diameter

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Fig. 15

Loss and loss to pressure recovery factor ratio versus nozzle number, at 86.2% operating point for 1 cm nozzle diameter

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Fig. 16

Turbine efficiency at three operating points, with and without injection

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Fig. 17

Axial velocity distribution at three operating points in one meter below turbine band, before injection

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Fig. 18

Effect of injection on axial velocity distribution at three operating points in one meter below turbine band

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