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research-article

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, Iran
moona_mohammadi@yahoo.com

Ebrahim Hajidavalloo

Mechanical Engineering Department, Shahid Chamran University of Ahvaz, Ahvaz, Iran
hajidae@scu.ac.ir

Morteza Behbahani-Nejad

Mechanical Engineering Department, Shahid Chamran University of Ahvaz, Ahvaz, Iran
bnmorteza@scu.ac.ir

1Corresponding author.

ASME doi:10.1115/1.4041565 History: Received April 04, 2018; Revised September 23, 2018

Abstract

In this paper, the effect of water, air and their combined injection from two different injection points are 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 SST k-? turbulence and two-phase models. Using an appropriate validation method, acceptable results were obtained under the non-injection 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 calculate the total loss in the draft tube. Comparing the results of the three types of injections shows that 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 is not suitable, but combination of these two fluids can improve system performance.

Copyright (c) 2018 by ASME
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