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Investigation of the unstable flow phenomenon in a pump turbine

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Abstract

Instability of pump turbine with S-shaped curve is characterized by large fluctuations of rotational speed during the transient processes. For investigating this phenomenon, a numerical model based on the dynamic sliding mesh method (DSSM) is presented and used to numerically solve the 3D transient flow which is characterized by the variable rotation speed of runner. The method is validated by comparison with measured data for a load rejection process in a prototype pump turbine. The results show that the calculated rotation speed agrees well with the experimental data. Based on the validated model, simulations were performed for the runaway process using an artificially assumed operating condition under which the unstable rotation speed is expected to appear. The results confirm that the instability of runner rotational speed can be effectively captured with the proposed method. Presented results include the time history profiles of unit flow rate and unit rotating speed. The internal flow characteristics in a typical unstable period are discussed in detail and the mechanism of the unstable hydraulic phenomenon is explained. Overall, the results suggest that the method presented here can be a viable alternative to predict the dynamic characteristics of pump turbines during transient processes.

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Abbreviations

A 1 :

Face area vector normal to the x directions [m2]

A 2 :

Face area vector normal to the y directions [m2]

D :

Diffusive flux

D*:

Reference diameter of runner [m]

E :

The strain rate tensor

F :

Convective flux

H :

Head [m]

J :

Moment of inertial [kg·m2]

M :

Axial moment [NM]

M f :

Axial moment induced by frictional force [NM]

M z :

Axial moment induced by pressure [NM]

n :

Rotation speed [rpm]

^n :

Unit vector normal to surface

n s :

Specific speed = n√P/H 1.25 [m·kW]

n 11 :

Unit rotation speed

p :

Pressure [Pa]

P :

Power [kW]

q :

Volume flow rate [l/s]

q 11 :

Unit flow rate

Q :

Conserved variable

S u :

Source term

t :

Time [s]

T :

One period

u :

Absolute velocity vector [m/s]

u b :

Velocity vector of mesh motion [m/s]

x, y :

Cartesian co-ordinates

ω:

Angular velocity [rad/s]

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Authors and Affiliations

  1. School of Mechanical Engineering, Shanghai Jiaotong University, Shanghai, 200240, China

    JunLian Yin & DeZhong Wang

  2. Department of Mechanical Engineering, Mississippi State University, Starkville, Mississippi, USA

    D. Keith Walters

  3. State Key Laboratory of Hydropower Equipment, Harbin, 150040, China

    XianZhu Wei

Authors
  1. JunLian Yin
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  2. DeZhong Wang
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  3. D. Keith Walters
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  4. XianZhu Wei
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Correspondence to JunLian Yin.

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Yin, J., Wang, D., Walters, D.K. et al. Investigation of the unstable flow phenomenon in a pump turbine. Sci. China Phys. Mech. Astron. 57, 1119–1127 (2014). https://doi.org/10.1007/s11433-013-5211-5

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  • DOI: https://doi.org/10.1007/s11433-013-5211-5

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