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Research Papers: Flows in Complex Systems

# Cavitation Characteristics of S-Blade Used in Fully Reversible Pump-Turbine

[+] Author and Article Information
T. M. Premkumar

Hydroturbomachines Laboratory,
Department of Mechanical Engineering,
Chennai 600036, India
e-mail: tmichamech@gmail.com

Pankaj Kumar

Hydroturbomachines Laboratory,
Department of Mechanical Engineering,
Chennai 600036, India
e-mail: pankaj20221@gmail.com

Dhiman Chatterjee

Hydroturbomachines Laboratory,
Department of Mechanical Engineering,
Chennai 600036, India
e-mail: dhiman@iitm.ac.in

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received June 11, 2013; final manuscript received January 1, 2014; published online March 10, 2014. Assoc. Editor: Zvi Rusak.

J. Fluids Eng 136(5), 051101 (Mar 10, 2014) (15 pages) Paper No: FE-13-1367; doi: 10.1115/1.4026441 History: Received June 11, 2013; Revised January 01, 2014

## Abstract

S-shaped blade profiles with double camber find use in fully reversible turbomachines that can extract power from tides. Though noncavitating characteristics of S-blades were determined in the past, yet characterizing cavitating flow was not carried out. This work, which is the first step in this direction, uses a two-pronged approach of experimental and numerical characterization of cavitating flow past these hydrofoils. Experimental results indicate that as the angle of attack increases in either positive or negative directions, cavitation inception number increases. Minimum cavitation effect is observed at 2 deg, which is zero lift angle of attack. For higher angles of attack ($±6deg$, $±4deg$) and moderate or low cavitation number ($σ/σi≤0.3$), unsteady cloud cavitation was characterized through visual observation and from pressure fluctuation data. It was observed that for unsteady cavity shedding to take place is the length and thickness of the cavity should be more than 50% and 10% of the chord length, respectively. Predicting flow past this geometry is difficult and the problem may be compounded in many applications because of laminar-to-turbulence transition as well as due to the presence of cavitation. Present simulations indicate that the $k-kL-ω$ transition model may be useful in predicting hydrodynamic performance of this type of geometry and for the range of Reynolds number considered in this paper. Hydrodynamic performance under cavitation indicates that pumping mode is more adversely affected by cavitation and, hence, a fully reversible turbomachine may not perform equally well in turbine and pump modes as expected from noncavitating results.

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## Figures

Fig. 1

Schematic of a S-shaped hydrofoils

Fig. 2

(a) Schematic of cavitation test setup. (b) Schematic showing lighting arrangement and position of camera.

Fig. 3

(a) Computational grid with zoomed view near S-blade surface; (b) grid independent study

Fig. 4

Variation of (a) lift and (b) lift-to-drag ratio with different angles of attack under noncavitating condition

Fig. 5

Variation of pressure coefficient over upper and lower surfaces for different angles of attack. (a) -6 deg, (b) -4 deg, (c) -2 deg, (d) 0 deg, (e) 2 deg, (f) 4 deg, and (g)

Fig. 6

Variation of Cτwx over upper and lower surfaces of S-shaped hydrofoil for different angles of attack

Fig. 7

Variation of inception and desinence cavitation number for different angles of attack. Also shown are variations of -Cpmin and numerical predictions of cavitation inception.

Fig. 8

Variation of x-component of velocity, turbulent kinetic energy and vapor fraction at x/c = 0.125 for -6 deg angle of attack at σ/σi=0.3

Fig. 9

Effect of Reynolds number on cavitation inception

Fig. 10

Photograph of cavitation for different cavitation number at -6 deg angle of attack. (a) σ/σi = 1.00, (b) σ/σi = 0.63, (c) σ/σi = 0.44, (d) σ/σi = 0.17. Color maps indicate numerical vapor contour levels.

Fig. 11

Frequency spectrum of variation of vapor fraction. Angle of attack is -6 deg at σ/σi = 0.3.

Fig. 12

Photograph of cavitation for different cavitation number at 6 deg angle of attack. (a) σ/σi = 0.74, (b) σ/σi = 0.48, (c) σ/σi = 0.28, (d) σ/σi = 0.07. Color maps indicate numerical vapor contour levels.

Fig. 13

Photograph of cavitation for different cavitation number at 0 deg angle of attack. (a) σ/σi = 1.00, (b) σ/σi = 0.69. Color maps indicate numerical vapor contour levels.

Fig. 14

Variation of (a) cavity length and (b) cavity thickness with cavitation number for different angles of attack

Fig. 15

Cavitation portrait chart indicating occurrences of different types of cavitation

Fig. 16

Variation of RMS value of pressure fluctuation with cavitation number for different angles of attack

Fig. 17

Comparison of experimental and numerical pressure fluctuations for angle of attack = -6 deg at σ/σi = 0.3

Fig. 18

Spectral analysis of pressure fluctuation due to cavitation for different angles of attack

Fig. 19

Temporal variation and frequency domain analysis of unsteady (a) lift coefficient and (b) drag coefficient

Fig. 20

Prediction of lift coefficient (CL), drag coefficient (CD) for different angles of attack and cavitation number

Fig. 21

Streamlines indicating extensive recirculation zone for angle of attack = -6 deg under noncavitating condition

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