Research Papers

Unsteady Computational Fluid Dynamic Analysis of the Behavior of Guide Vane Trailing‐Edge Injection and Its Effects on Downstream Rotor Performance in a Francis Hydroturbine

[+] Author and Article Information
Bryan J. Lewis

2600 S. Second Street,
Duncan, OK 73536-0450
e-mail: bryan.lewis@halliburton.com

John M. Cimbala

Depament of Mechanical and
Nuclear Engineering,
The Pennsylvania State University,
234 Reber Building,
University Park, PA 16802
e-mail: jmcimbala@psu.edu

1 Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 18, 2014; final manuscript received December 12, 2014; published online January 28, 2015. Assoc. Editor: Anestis I. Kalfas.

J. Turbomach 137(8), 081001 (Aug 01, 2015) (9 pages) Paper No: TURBO-14-1157; doi: 10.1115/1.4029427 History: Received July 18, 2014; Revised December 12, 2014; Online January 28, 2015

A unique guide vane design, which includes trailing-edge jets, is presented for a mixed-flow Francis hydroturbine. The water injection causes a change in bulk flow direction at the inlet of the rotor. When properly tuned, altering the flow angle results in a significant improvement in turbine efficiency during off-design operation. Unsteady CFD simulations show nearly 1% improvement in overall turbine efficiency with the use of injection. This revolutionary concept also has the ability to reduce the intensity of the rotor–stator interactions (RSI) by compensating for the momentum deficit of the wicket gate wakes. This technology may be equally applied to other turbomachinery devices with problematic rotor–stator flow misalignments.

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Fig. 1

Final design of the trailing-edge geometry for the jet channels added to the wicket gates of the GAMM Francis Turbine. The blunt trailing edge was replaced with a beveled shape, and the jets were inclined toward the center of the vane to improve the maximum turning of the water.

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Fig. 2

Geometry used for the various CFD simulations needed to evaluate the design of the wicket gate trailing-edge jets, and the impact on the turbine performance. (a) 2D distributor passage. (b) 3D full-wheel simulation of the GAMM turbine.

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Fig. 3

Meridional profile of the GAMM turbine, showing the primary geometric measurements of the turbine and the flow survey locations. (Source: GAMM Proceedings [25] (units in mm).)

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Fig. 4

Sensitivity of the solution to changes in mesh refinement, obtained by individually modeling the flow through each component of the turbine. Markers with error bars indicate experimental measurements. (a) Distributor, (b) runner, and (c) draft tube.

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Fig. 5

Instantaneous velocity contour plots (in m/s) for the flow in the 2D periodic distributor vane channel with both a blunt trailing edge and a beveled trailing edge. (a) Blunt trailing edge, no injection, (b) blunt trailing edge, with injection, and (c) beveled trailing edge, no injection.

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Fig. 6

Unsteady moment on the wicket gate with the original blunt trailing edge, with and without injection, and a beveled trailing edge. The negative value indicates a closing moment, which is required for operational safety. As these are 2D simulations, the measured torque represents a per unit length value.

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Fig. 7

Frequency spectra obtained from DFTs of the computed surface forces. Data are shown for the BEP, low flow, and low flow with injection cases. The fundamental machine frequencies and blade passing frequencies are clearly visible for each operating point. (a) BEP, (b) low flow, and (c) low flow with injection.

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Fig. 8

Unsteady torque on an individual runner blade, shown in physical units, and plotted with respect to the revolutions of the runner. Data for the BEP, low flow, and low flow with injection cases are shown. Fluctuations in torque were observed every 15 deg of the runner rotation, corresponding to the time period for a blade to pass between two wicket gates. Additional lower frequency variations were also observed. (a) BEP, (b) low flow, and (c) low flow with injection.

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Fig. 9

Instantaneous contours of velocity magnitude in the distributor and runner region for the BEP, low flow, and low flow with injection cases, showing the changes in flow behavior near the runner for the three operation conditions. Contours were taken at constant values of Z at two locations along the runner span. (a) BEP, (b) low flow, and (c) low flow with injection.

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Fig. 10

Instantaneous surface-streamlines along the runner blade, and surface pressure contour, for the BEP, low flow, and low flow with injection cases. The surface-streamlines are analogous to oil streaklines. Images generated in FieldView 13. (a) BEP, (b) low flow, and (c) low flow with injection.

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Fig. 11

Instantaneous contours of pressure distribution on the leading edge of the runner blade, where the blade connects to the band, for the BEP, low flow, and low flow with injection cases. Each view is aligned with the leading edge of the runner, with the pressure side on the left and suction side on the right (units of reduced pressure p = P/ρ in m2/s2).




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