Analysis of the dynamic response of pump-turbine impellers. Influence of the rotor

Egusquiza, Eduard; Valero, Carme; Presas, Alexandre; Huang, Xiaoxu; Guardo, Alfredo; Seidel, U.

doi:10.1016/j.ymssp.2015.05.034

Cited by 52 publications

(40 citation statements)

References 12 publications

(15 reference statements)

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“…In the past, natural frequencies and mode shapes of these kind of structures have been obtained [17,39,43] but without fully determining the FRF (therefore no damping ratios were obtained). For such structures, PZTs have been proved to be more suitable exciters for physical reasons (inaccessibility of the structure) [17] and this paper shows also that the use of them gives generally more realistic estimations of the damping ratios and therefore more accurately predictions of the amplitude of the FRF than other classical exciters used in EMA.…”

Section: Determination Of the Frf For Submerged Structures With Nementioning

confidence: 99%

Accurate Determination of the Frequency Response Function of Submerged and Confined Structures by Using PZT-Patches†

Presas

Valentín

Valero

et al. 2017

Sensors

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To accurately determine the dynamic response of a structure is of relevant interest in many engineering applications. Particularly, it is of paramount importance to determine the Frequency Response Function (FRF) for structures subjected to dynamic loads in order to avoid resonance and fatigue problems that can drastically reduce their useful life. One challenging case is the experimental determination of the FRF of submerged and confined structures, such as hydraulic turbines, which are greatly affected by dynamic problems as reported in many cases in the past. The utilization of classical and calibrated exciters such as instrumented hammers or shakers to determine the FRF in such structures can be very complex due to the confinement of the structure and because their use can disturb the boundary conditions affecting the experimental results. For such cases, Piezoelectric Patches (PZTs), which are very light, thin and small, could be a very good option. Nevertheless, the main drawback of these exciters is that the calibration as dynamic force transducers (relationship voltage/force) has not been successfully obtained in the past. Therefore, in this paper, a method to accurately determine the FRF of submerged and confined structures by using PZTs is developed and validated. The method consists of experimentally determining some characteristic parameters that define the FRF, with an uncalibrated PZT exciting the structure. These parameters, which have been experimentally determined, are then introduced in a validated numerical model of the tested structure. In this way, the FRF of the structure can be estimated with good accuracy. With respect to previous studies, where only the natural frequencies and mode shapes were considered, this paper discuss and experimentally proves the best excitation characteristic to obtain also the damping ratios and proposes a procedure to fully determine the FRF. The method proposed here has been validated for the structure vibrating in air comparing the FRF experimentally obtained with a calibrated exciter (impact Hammer) and the FRF obtained with the described method. Finally, the same methodology has been applied for the structure submerged and close to a rigid wall, where it is extremely important to not modify the boundary conditions for an accurate determination of the FRF. As experimentally shown in this paper, in such cases, the use of PZTs combined with the proposed methodology gives much more accurate estimations of the FRF than other calibrated exciters typically used for the same purpose. Therefore, the validated methodology proposed in this paper can be used to obtain the FRF of a generic submerged and confined structure, without a previous calibration of the PZT.

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Section: Determination Of the Frf For Submerged Structures With Nementioning

confidence: 99%

Accurate Determination of the Frequency Response Function of Submerged and Confined Structures by Using PZT-Patches†

Presas

Valentín

Valero

et al. 2017

Sensors

Self Cite

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“…Figure 1b shows a bladed-disk Figure 1. Examples of rotating structures involving disks: (a) Simple Disk structure [3], (b) Bladed disk structure [4], (c) Disk-blade assembly [5], and (d) Disk-blades-disk assembly [6].…”

Section: Introductionmentioning

confidence: 99%

Experimental Measurements of the Natural Frequencies and Mode Shapes of Rotating Disk-Blades-Disk Assemblies from the Stationary Frame

et al. 2019

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Determining the natural frequencies and mode shapes of rotating turbomachinery components from both rotating and stationary reference frames is of paramount importance to avoid resonance problems that could affect the normal operation of the machine, or even cause critical damages in these components. Due to their similarity to real engineering cases, this topic has been experimentally analyzed in the past for disk-shaft assemblies and rotor disk-blades assemblies (bladed-disk or blisk). The same topic is less analyzed for disk-blades-disk assemblies, although such configurations are widely used in centrifugal closed impellers of compressors, hydraulic pumps, pump-turbines, and runners of high head Francis turbines. In this paper, experimental measurements, varying the rotating speed of a disk-blade-disk assembly and exciting the first natural frequencies of the rotating frame, have been performed. The rotating structure is excited and measured by means of PZT patches from the rotating frame and with a Laser Doppler Vibrometer (LDV). In order to interpret the experimental results obtained from the stationary frame, a method to decompose the diametrical mode shapes of the structure in simple diametrical components (which define the diametrical mode shapes of a simple disk) has been proposed. It is concluded that the resonant frequencies detected with a stationary sensor correspond to the ones predicted with the decomposition method. Finally, a means to obtain equivalent results with numerical simulation methods is shown.

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“…This means that hydro units regulate their power depending on the other renewable sources' production to ensure the stability of the grid and to satisfy the energy demand. However, when hydraulic turbines regulate their power below and above their best efficiency point (BEP), they present different dynamic problems [4][5][6][7] which affect the useful life of the mechanical parts of the turbine.…”

Section: Introductionmentioning

confidence: 99%

Transmission of High Frequency Vibrations in Rotating Systems. Application to Cavitation Detection in Hydraulic Turbines

et al. 2018

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Abstract:One of the main causes of damage in hydraulic turbines is cavitation. While not all cavitation appearing in a turbine is of a destructive type, erosive cavitation can severely affect the structure, thus increasing maintenance costs and reducing the remaining useful life of the machine. Of all types of cavitation, the maximum erosion occurs when clouds of bubbles collapse on the runner surface (cloud cavitation). When this occurs it is associated with a substantial increase in noise, and vibrations that are propagated everywhere throughout the machine. The generation of these cavitation clouds may occur naturally or it may be the response to a periodic pressure fluctuation, like the rotor/stator interaction in a hydraulic turbine. Erosive bubble cavitation generates high-frequency vibrations that are modulated by the shedding frequency. Therefore, the methods for the detection of erosive cavitation in hydraulic turbines are based on the measurement and demodulation of high-frequency vibrations. In this paper, the feasibility of detecting erosive cavitation in hydraulic turbines is investigated experimentally in a rotating disk system, which represents a simplified hydraulic turbine structure. The test rig used consists of a rotating disk submerged in a tank of water and confined with nearby axial and radial rigid surfaces. The excitation patterns produced by cloud cavitation are reproduced with a PZT (piezoelectric patch) located on the disk. These patterns include pseudo-random excitations of different frequency bands modulated by one low carrier frequency, which model the erosive cavitation characteristics. Different types of sensors have been placed in the stationary and in the rotating parts (accelerometers, acoustic emission (AE), and a microphone) in order to detect the excitation pattern. The results obtained for all the sensors tested have been compared in detail for the different excitation patterns applied to the disk. With this information, the best location and type of sensor to detect the different excitations have been identified. This study permits improving the actual technique of detecting erosive cavitation in hydraulic turbines and, therefore, to avoid operation under these circumstances.

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Analysis of the dynamic response of pump-turbine impellers. Influence of the rotor

Cited by 52 publications

References 12 publications

Accurate Determination of the Frequency Response Function of Submerged and Confined Structures by Using PZT-Patches†

Accurate Determination of the Frequency Response Function of Submerged and Confined Structures by Using PZT-Patches†

Experimental Measurements of the Natural Frequencies and Mode Shapes of Rotating Disk-Blades-Disk Assemblies from the Stationary Frame

Transmission of High Frequency Vibrations in Rotating Systems. Application to Cavitation Detection in Hydraulic Turbines

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