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Research Papers: Flows in Complex Systems

Experimental Investigation of the Interblade Flow in a Kaplan Runner at Several Operating Points Using Laser Doppler Anemometry

[+] Author and Article Information
Kaveh Amiri

Department of Engineering
Science and Mathematics,
Luleå University of Technology,
Luleå 97187, Sweden
e-mail: kaveh.amiri@ltu.se

Berhanu Mulu

Vattenfall Research and Development,
Älvkarleby 81470, Sweden
e-mail: berhanu.mulu@vattenfall.com

Michel J. Cervantes

Professor
Department of Engineering
Science and Mathematics,
Luleå University of Technology,
Luleå 97187, Sweden;
Department of Energy and Process Engineering,
Water Power Laboratory,
Norwegian University of
Science and Technology,
Trondheim 7491, Norway
e-mail: michel.cervantes@ltu.se

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received January 16, 2015; final manuscript received September 11, 2015; published online October 23, 2015. Assoc. Editor: Bart van Esch.

J. Fluids Eng 138(2), 021106 (Oct 23, 2015) (12 pages) Paper No: FE-15-1031; doi: 10.1115/1.4031609 History: Received January 16, 2015; Revised September 11, 2015

This paper presents laser Doppler anemometry (LDA) measurements within the runner blade channels and at the runner outlet of a Kaplan turbine model. The model was investigated at six operating points located on two propeller curves of the turbine to study the flow condition during on-cam and off-cam operations. Main and secondary flows within and after the runner were analyzed, and the effects of the hub and tip clearances on the velocity fields within and after the runner were evaluated. Operation of the turbine at flow rates that are lower than the designed rate for the corresponding propeller curve resulted in vortex breakdown and the formation of a rotating vortex rope (RVR). The RVR formation produced an asymmetrical velocity distribution within and after the runner. The results demonstrated the occurrence of an oscillating flow with the same frequency as the vortex rope within the blade channels located upstream of the RVR. This results in an asymmetric flow through the runner and oscillating forces on the runner blades. The measured velocities indicated that the geometrical asymmetries in the runner manufacturing process resulted in various flow asymmetries at the measured sections. The asymmetries were up to 3% within the runner and 7% at the runner outlet.

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References

Figures

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Fig. 1

Sketch of the RVR inside the draft of a Francis turbine [15]

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Fig. 2

Sketch of the model illustrating the spiral casing, distributor, and draft tube

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Fig. 3

Schematic of the hub and tip clearances: (a) side view of the runner, (b) bottom view of the runner, (c) hub clearance at the trailing edge, (d) tip clearance at the leading edge, (e) tip clearance at the trailing edge, and (f) vortices formed at the runner blade’s hub and tip

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Fig. 4

(a) LDA measurement locations; Center: radius along the runner hub center; RB: measurement section between the runner blades; RC: measurement section below the runner blades. (b) Sketch of the optical access windows; the dashed lines in (b) represent the window’s centerline. The top glass center is aligned with the runner hub center.

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Fig. 5

Differences between the blade geometries close to the trailing edge at r* = 0.91

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Fig. 6

Amplitude spectra of dynamic pressure obtained from tangential velocity components within the runner at BEP0.8

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Fig. 7

Illustration of the phase-averaged velocity over one runner revolution; the initial signal contains 358 ks, and the bin size used for the phase averaging is Δθ = 1 deg

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Fig. 8

Phase-averaging bin center positions in the runner blade passage relative to the runner blades, top view

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Fig. 9

Time-averaged velocity profiles within the runner and at the runner outlet: (a) axial and tangential velocity profiles at section RB. (b) Axial and tangential velocity profiles at the runner outlet: BEP0.8. The bold lines at approximately r* = 0.4 and r* = 0.5 represent the runner hub.

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Fig. 10

Reynolds stresses u*2, v*2, and uv*: (a) within the blade channels, and (b) at the runner outlet at the BEP0.8. The bold lines at approximately r* = 0.4 and r* = 0.5 represent the runner hub.

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Fig. 11

Normalized phase-averaged velocities with the corresponding RMS values at section RB: BEP0.8

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Fig. 12

Deviation of the axial and tangential velocity contours in different blade channels from the mean contour: BEP0.8

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Fig. 13

Normalized phase-averaged velocities at the runner outlet: BEP0.8

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Fig. 14

Phase-averaged deviation of the axial and tangential velocity contours in different blade channels from the mean contour at the runner outlet: BEP0.8

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Fig. 15

Time-averaged velocity profiles at PL0.8 (a) within the runner and (b) at the runner outlet

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Fig. 16

Normalized phase-averaged velocities with respect to the runner frequency at the runner outlet: PL0.8. The dashed gray circle shows the RVR center at the trailing edge of the runner hub.

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Fig. 17

Amplitude of the dynamic pressure obtained from axial and tangential velocity measurement results at the RVR frequency

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Fig. 18

Normalized phase-averaged axial and tangential velocities with respect to the RVR frequency at the runner outlet: PL0.8

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Fig. 19

Normalized phase-averaged contours of the oscillating axial and tangential velocities with respect to the RVR frequency within the runner: PL0.8

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