Experimental investigation on the effect off near walls on the eigen frequency of a low specific speed francis runner

Østby, Petter Thorvald Krogh; Sivertsen, Kjell; Billdal, Jan Tore; Haugen, Bjørn Olav

doi:10.1016/j.ymssp.2018.08.060

Cited by 14 publications

(13 citation statements)

References 20 publications

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“…e blade mode is a deflection pattern of the runner where the blades have the largest amplitude, while the disc mode is a deflection pattern of the runner where the hub and shroud have the largest amplitudes. Modes with high deflection of the hub and ring, disc modes, could have higher damping due to the surrounding water and structure in the housing compared to blade modes [10].…”

Section: Rsi Excitationmentioning

confidence: 99%

“…Major findings included that the modes with large movement of hub and shroud, the global modes, disappeared when the runner was mounted in the housing. e blade modes were minimally affected by the housing [10]. Valentín et al analyzed the natural frequencies of a prototype turbine through impact excitation in air and later, pressure field excitation while in operation.…”

Section: Introductionmentioning

confidence: 99%

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Experimental Study of a Low‐Specific Speed Francis Model Runner during Resonance

Agnalt

Østby

Solemslie

et al. 2018

Shock and Vibration

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An analysis of the pressure in a runner channel of a low-specific speed Francis model runner during resonance is presented, which includes experiments and the development of a pressure model to estimate both the convective and acoustic pressure field from the measurements. The pressure was measured with four pressure sensors mounted in the runner hub along one runner channel. The mechanical excitation of the runner corresponded to the forced excitation from rotor-stator interaction. The rotational speed was used to control the excitation frequency. The measurements found a clear resonance peak in the pressure field excited by the second harmonic of the guide vane passing frequency. From the developed pressure model, the eigenfrequency and damping were estimated. The convective pressure field seems to diminish almost linearly from the inlet to outlet of the runner, while the acoustic pressure field had the highest amplitudes in the middle of the runner channel. At resonance, the acoustic pressure clearly dominated over the convective pressure. As the turbine geometry is available to the public, it provides an opportunity for the researchers to verify their codes at resonance conditions.

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Section: Rsi Excitationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Experimental Study of a Low‐Specific Speed Francis Model Runner during Resonance

Agnalt

Østby

Solemslie

et al. 2018

Shock and Vibration

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“…e static pressure load is positively correlated with the flow rate passing through the runner, and the dynamic pressure load mostly comes from the rotor-stator interaction (RSI) [6,7]. e modal behavior of Francis turbine runners and pump-turbine runners has been widely studied [8][9][10][11][12][13][14]. However, few investigations of the dynamic behavior of Kaplan turbine runners have been undertaken before.…”

Section: Introductionmentioning

confidence: 99%

Numerical Model on the Dynamic Behavior of a Prototype Kaplan Turbine Runner

Zhang

Chen

2021

Mathematical Problems in Engineering

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Experimental and numerical investigations of the modal behavior of a prototype Kaplan turbine runner in air have been conducted in this paper. The widely used roving accelerometer method was used in the experimental modal analysis. A systematic approach from a single blade model to the whole runner has been used in the simulation to get a thorough understanding. The experimental results show that all the detected modes concentrate their displacements on the impacted blade. The numerical results show that the modes of the single blade form different mode families of the runner, and each mode family corresponds to a narrow frequency band. Harmonic response analysis shows that, at the response peak point, the single blade excitation can only get mode shapes with concentrations on the exciting blade due to the superposition of the close modes in each mode family, which explains the experimental results well, while the mode superposition can be avoided by the order excitation method. With the reduction of the connection stiffness between the blades and hub/control system, the frequencies of most modes change from insensitive to more and more sensitive to the connection stiffness change, which results in a sensitive area and an insensitive area. Through comparison with the experimental results, it is indicated that the natural frequencies of the runner can probably be predicted by merging the runner into a whole body.

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“…The effect of the added mass on the dynamic response was proposed and discussed. Østby et al [5] studied the added mass effect of water on a simplified low specific speed Francis turbine runner using an experimental method. The measurements revealed a frequency reduction of about 40% when the runner was hanging in water.…”

Section: Introductionmentioning

confidence: 99%

“…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.…”

Section: Introductionmentioning

confidence: 99%

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

Liu

Xia

Yang

et al. 2021

JMSE

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To predict the resonance characteristics of hydraulic machinery, it is necessary to accurately calculate the natural modes of the runners in the operating environment. However, in the existing research, the boundary conditions of the numerical modal analysis of the runner were not unified. In this paper, numerical modal analysis of a prototype Francis pump turbine runner was carried out using the acoustic–structure coupling method. The results of three different constraints were compared. The influence of the energy loss on the chamber wall on the natural modes of the runner was studied by the absorption boundary. The results show that the constraint condition (especially the rotating shaft) has significant impacts on the torsional mode, the radial mode, the 1 nodal-diameter mode, and the 0 nodal-circle mode, and the maximum differences in the natural frequencies under different conditions are 69.3%, 56.4%, 35.1%, and 9.4%, respectively. The change of the natural frequencies is closely related to the modal shapes. On the other hand, the energy loss on the wall mainly affects the nodal-circle modes, and the influence on other modes is negligible. The results can provide references for the design and resonance characteristics analysis of hydraulic machinery runners.

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Experimental investigation on the effect off near walls on the eigen frequency of a low specific speed francis runner

Cited by 14 publications

References 20 publications

Experimental Study of a Low‐Specific Speed Francis Model Runner during Resonance

Experimental Study of a Low‐Specific Speed Francis Model Runner during Resonance

Numerical Model on the Dynamic Behavior of a Prototype Kaplan Turbine Runner

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

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