Research Papers: Ocean Renewable Energy

Unsteady RANS Simulations of Wells Turbine Under Transient Flow Conditions

[+] Author and Article Information
Qiuhao Hu

Multifunctional Ship Model Towing Tank,
School of Naval Architecture
Ocean & Civil Engineering,
Shanghai Jiao Tong University,
800 Dongchuan Road,
Shanghai 201100, China
e-mail: huecu588755@sjtu.edu.cn

Ye Li

Multifunctional Ship Model Towing Tank,
School of Naval Architecture
Ocean & Civil Engineering,
Shanghai Jiao Tong University,
800 Dongchuan Road,
Shanghai 201100, China
e-mail: ye.li@sjtu.edu.cn

1Corresponding author.

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received January 23, 2017; final manuscript received August 11, 2017; published online September 29, 2017. Assoc. Editor: Ould el Moctar.

J. Offshore Mech. Arct. Eng 140(1), 011901 (Sep 29, 2017) (11 pages) Paper No: OMAE-17-1015; doi: 10.1115/1.4037696 History: Received January 23, 2017; Revised August 11, 2017

This paper presents our recent numerical simulations of a high-solidity Wells turbine under both steady and unsteady conditions by solving Reynolds-averaged Navier–Stokes (RANS) equations. For steady conditions, the equations are solved in a reference frame with the same angular velocity of the turbine. Good agreement between numerical simulation result and experimental data has been obtained in the operational region and incipient stall conditions. The exact value of stall point has been accurately predicted. Through analyzing the detailed fluid fields, we find that the stall occurs near the tip of the blade while the boundary layer keeps attached near the hub, due to the effect of radial flow. For unsteady conditions, two types of control methods are studied: constant angular velocity and constant damping moment. For the constant angular velocity, the behaviors of the turbine under both high and low sea wave frequency are calculated to compare with those obtained by quasi-steady method. The hysteresis characteristic can be observed and deeply affects the behaviors of the Wells turbine with high wave frequency. For the constant damping moment, the turbine angular velocity is time dependent. Under sinusoidal flow, the incident flow velocity in the operational region can be improved to avoid the stall.

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Fig. 1

Illustration of the OWC system (Adapted from Li and Yu [2])

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Fig. 2

Illustration of Wells turbine

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Fig. 3

Definition of sweep ratio

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Fig. 4

Near wall mesh conditions

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Fig. 5

Computational domain (a) reference frame and (b) moving mesh

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Fig. 6

Turbine torque results with respect to different grid numbers (a) reference frame and (b) moving mesh

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Fig. 7

Comparison of numerical results and experimental data in steady condition: (a) torque coefficient, (b) pressure drop coefficient, and (c) efficiency

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Fig. 8

Relative velocity contours downstream the blade: (a) ϕ = 0.24 and (b) ϕ = 0.28 (r = 135 mm)

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Fig. 9

The pressure distribution along the chord in r = 135 mm

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Fig. 10

Relative velocity contour downstream the blade

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Fig. 11

(a) Axial velocity components and (b) radial velocity components versus different radii along the chord. The origin for the position is the vertical line through the hub center in Fig. 3.

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Fig. 12

Stream line near the leading edge of the blades

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Fig. 13

Hysteresis characteristic: (a) torque coefficient, for ϕ0 = 0.22, (b) torque coefficient, for ϕ0 = 0.26, (c) pressure drop coefficient, for ϕ0 = 0.22, and (d) pressure drop coefficient, for ϕ0 = 0.26

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Fig. 14

Comparison of coefficients in acceleration process, decelerate process, and quasi-steady conditions: (a) mean torque coefficient and (b) mean pressure drop coefficient

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Fig. 15

Comparison of (a) mean torque coefficient and (b) mean pressure drop coefficient in unsteady conditions in a whole period and quasi-steady conditions

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Fig. 16

Angular velocity for T = 4 s and T = 8 s

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Fig. 17

Angular velocity in the acceleration process (incident velocity improved from 19.129 m/s to 24.987 m/s in 0.88 s)

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Fig. 18

Comparison of torque under steady and unsteady flows, for ϕ0 = 0.28

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Fig. 19

Torque of two control methods under sinusoidal incident flow

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Fig. 20

Comparison of the numerical results between moving mesh and reference frame

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Fig. 21

Comparison of the numerical results between moving mesh and reference frame




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