Evaluation of gap influence on the dynamic response behavior of pump-turbine runner

Abstract

Purpose The gaps between runner and nearby structures play an important role in the dynamic response of runner, especially for pump-turbines. This paper aims to evaluate the gap influence on the added mass and dynamic stress of pump-turbine runner and provide an improved method to predict the resonance of runner. Design/methodology/approach Acoustic-structural coupling method was used to evaluate the added mass factors of a reduced scale pump-turbine with different axial and radial gap size between runner and nearby rigid walls. Improved one-way fluid-structural interaction (FSI) simulation was used to calculate the dynamic stress of the runner, which takes into account fluid added mass effect. The time-dependent hydraulic forces on the runner surfaces that were obtained from unsteady CFD simulation were transferred to the runner structure as a boundary condition, by using mesh-matching algorithm at the FSI surfaces. Findings The results show that the added mass factors increase as the gap size decreases. The axial gaps have greater influence on the added mass factors for the in-phase (IP) modes than the counter-phase (CP) and crown-dominant (CD) modes, while the CP and CD modes are very sensitive to the radial gaps. The largest added mass factor is observed in (2 + 4)ND-CP mode (resonance mode). The results reveal that the transient structural dynamic stress analysis, with the consideration of gaps and fluid added mass, can accurately predict the resonance phenomenon. Resonance curve of the pump-turbine has been obtained which agrees well with the test result. The gap fluid has great influence on the resonance condition, while for non-resonance operating points, the effect of gaps on the dynamic stress amplitude is quite small. Originality/value This paper provides an accurate method to analyze the dynamic response during runner design stage for safety assessment. The resonance curve prediction has more significance than previous methods which predict the resonance of runner by modal or harmonic analysis.

Investigation on Dynamic Stresses of Pump-Turbine Runner during Start Up in Turbine Mode

“…In traditional FSI simulation, only loads on inner surface are considered. However, the loads on outer surface also have a great influence on the stress-state of runner [25] and were considered in this paper.…”

Effect of Boundary Conditions on Fluid–Structure Coupled Modal Analysis of Runners

“…The fixed constraints were set on the shaft-connecting The geometry of the runner is much more complicated than that of the disk. Therefore, there are some special vibration patterns in ND and NC modes, such as crown dominant (CD), band dominant (BD), and counter phase (CP) [15]. In addition, the modes of the runner also include the vibration modes dominated by blades.…”

“…Additionally, the smaller the thickness, the more significant the influence. Similarly, He et al [15] studied the effect of the clearance on the dynamic characteristics of a pump turbine runner using the acoustic-structure coupling method. The results showed that the thickness of the clearance between the runner and the wall has a significant impact on the resonance condition.…”

“…However, in the research of the dynamic characteristics of the runners, the setting of the constraints is not uniform. Without considering the rotating shaft, line constraint (i.e., fixed constraint on bolt center line) [11,12], surface constraint (i.e., fixed constraint on connecting surface) [15] and rope suspension [2,5,6] are often adopted. Among them, the rope suspension is usually used in the experimental modal analysis to eliminate the influence of constraints or other structures on the dynamic characteristics.…”

Effect of Operating Head on Dynamic Behavior of a Pump–Turbine Runner in Turbine Mode

“…Thus, some researchers have tried to simplify the N-S equation; a widely used method is the acoustic fluid-structural coupling method [6]. He et al investigated the modal characteristics and the dynamic response characteristics of a pump-turbine runner and discussed the added mass effect in detail [7]. Lais characteristics of a Francis turbine runner on the basis of the acoustic fluid-structural coupling method [8], and the numerical method was verified by the experimental results.…”