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In recent decades, in order to increase output power of hydroelectric turbomachinery, the design head and the flow rate of the hydraulic turbines have been increased greatly. This has led to serious vibratory problems. The pump-turbines have to work at various operation conditions to satisfy the requirements of the power grid. However, larger hydra...
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Citations
... In SNL and runaway, the amplitudes of the broad-band pressure oscillations exhibit a further increase. Despite their dominance for low-specific-speed turbines near the BEP [28][29][30][31][32], the pressure fluctuations due to the rotor-statorinteraction become less significant compared to the chaotic pressure fluctuations of DPL [23,33]. Excluding operational transients [34][35][36], DPL and SNL yield the highest fatigue damage for hydroelectric impellers [31]. ...
To meet the increasing demand for higher flexibility in hydropower, an operating range extension in an existing hydroelectric powerplant is considered. To this end, the dynamic flow and structural behavior of the low-head pump-turbine is investigated in turbine mode in partial load and deep partial load conditions, to evaluate the feasibility of this flexibilization due to the increased high cycle fatigue damage. In a first step, different numerical simulation approaches that combine fluid dynamics and structural dynamics are applied and compared to in-situ dynamic strain and pressure measurements on the impeller. As a result, the modelling requirements for a numerical workflow that leads to unmatched accuracy in predicting the broad-band dynamic stresses of deep partial load are identified. In a second step, the operating-point-dependent fatigue crack initiation spots are identified based on dynamic stresses. Herein, the emergence of an additional dominant critical spot near the blade leading edge is observed, which is unexpected for low-head pump turbines. Thanks to the detailed numerical flow and structural analyses, the root cause for the dynamic stress concentration is studied and the emergence of the new critical spot is understood. It turns out in deep partial load, that the main source of pressure oscillations on the impeller blade surfaces is the vortex-dominated flow detachment zone around the blade leading edge, which, in combination with the geometry of the investigated impeller, translates into the main stress oscillations. The results of this work were later used to extend the operating range of the hydroelectric powerplant from initially 25% to 100% power output to now 0% to 100%.
... However, the two generations of disc pumps have their own application scenarios, and the second generation of disc pumps is not a substitute for the first generation. The first generation of bladeless disc pumps has more advantages than the second generation of blade disc pumps in some cases with high media protection [125][126][127][128]. ...
Disc pumps have obvious advantages in dealing with difficult-to-pump media. Energy efficiency and sustainable energy management are important topics with regard to reducing costs and promoting carbon neutrality. Though the concept of the disc pump was proposed in the 1850s, development was slow and limited by its initial model. However, with the development of industries such as petrochemicals and food, the efficient pumping of difficult-to-pump media is much needed, but facing challenges. Therefore, research on energy-efficient disc pumps is particularly important moving forward. In this paper, the available information from the open literature about the research and development of the disc pump will be thoroughly reviewed. It focuses on the historical development, energy efficiency and physical model application of the disc pump. The review ends with a proposal for the direction of future development, and in this aspect, it is proposed that the energy efficiency prediction model based on velocity slip theory, the energy management system based on multi-scenarios and the design method based on energy conversion theory are important. The latest achievements in energy conversion are given. This review also provides a new perspective for the development of energy-efficient disc pumps.
... Submerged disk-like structures are relevant in several fields such as mechanical and civil engineering. This is because a disk can be used as a simplified model of many complex structures with similar dynamic response, as has been done for hydraulic turbomachinery, where, the modal behavior of a disk is similar to the modal behavior of critical components such as pump-turbine runners, high head Francis runners or centrifugal pumps [1,2]. ...
... constant value of the straight-line equation y(t) (mm s − 1 ) c 1 proportionally constant (kg s − 1 ) c 2 proportionally constant (kg m − 1 ) When a structure vibrates in a viscous fluid, part of the vibration energy is dissipated in the fluid and this is known as added damping or fluid damping. The added damping on disk-like structures has been studied by some authors [14][15][16][17][18][19][20][21][22]. ...
... In order to avoid resonances, it is of paramount importance to measure and precisely calculate the natural frequencies of hydraulic turbines in air and water under non-rotating and rotating conditions. Previous studies showed that there are many similarities between the mode shapes of some specific runners, such as Francis runners, and those of a disk [6][7][8][9]. More specifically, some modes of both a Francis runner and a disk are characterized by the number of nodal diameters (ND) and circles (NC). ...
The current paper presents an investigation into novel modal testing methods applied to a disk–shaft structure at different rotating speeds in air and water. The structure was excited using three different methods: an instrumented hammer, a piezoelectric PZT patch glued on the disk and a transient ramp-up. The structural response was measured using an accelerometer and strain gauges mounted on board as well as accelerometers and displacement lasers mounted off board. The potential to excite the natural frequencies using each excitation method and to detect natural frequencies with each sensor was analyzed and compared. Numerical structural and acoustic–structural modal and harmonic analyses of the non-rotating disk in air and water were also performed, taking into consideration the PZT patch. The numerical results showed a close agreement with the experimental ones in both air and water. It was found that the rotating speed of the disk modified the detected natural frequencies, depending on the frame of reference of the sensor. Finally, the PZT patch and the transient ramp-up were proven to be reliable methods to excite the natural frequencies of the current test rig and to be potentially applicable in full-scale hydraulic turbines under operating conditions.
... Nevertheless, to make experimental characterization of the modal parameters in real machine runners is not a trivial task as the structure is IOP Publishing doi:10.1088/1755-1315/1079/1/012091 2 confined, submerged and rotating. Therefore, in order to analyze these parameters, simplified models as simple disk structures have been used, which show similar mode shapes [12,13]. ...
In order to satisfy the power demand in the electrical grid, hydraulic turbine units frequently work under off-design operation conditions and pass through transient events. These operation conditions can lead to high vibration amplitudes in the turbine runners, decreasing their useful life, and in some cases to premature failures. To determine and to understand the behaviour of the fluid damping is a relevant topic, because this parameter limits the maximum amplitude in resonance conditions. The runner of some types of turbines, such as reversible pump-turbine and high head Francis turbine, can be modelled as a disk-like structure, due to their similar mode shapes. Because of this, in this work, the fluid damping of a vibrating disk was studied. The disk was submerged in water and was put in a resonant state at different vibration amplitudes. Moreover, this structure was excited at different distances to a rigid surface, in order to analyse the effects of the distance between the runner and the casing. The main effects on the fluid damping were determined and characterized, showing a dependency of the fluid damping ratio on the different parameters.
... Similarly, for experimental procedures and analytical studies, it can be convenient to analyze simplified models of complex structures with similar dynamic response. Huang et al. [14] studied the dynamic behaviour of a pump-turbine runner by numerical simulation. The runner was modeled as a disk-blade-disk structure that had the same mode shapes. ...
To prevent lifetime shortening and premature failure in turbine runners, it is of paramount importance to analyse and understand its dynamic response and determine the factors that affect it. In this paper, the dynamic response of a Kaplan runner is analysed in air by numerical and experimental methods. First, to start the analysis of Kaplan runner mode shapes, its geometry is simplified and modelled as a bladed disk. Bladed disks with different blade numbers are investigated, by numerical simulation, in order to understand the influence of this parameter on its modal characteristics. Then, mode shapes extracted are characterized and a classification is proposed. Second, an existing Kaplan runner is simulated by Finite Elements Method (FEM) and its mode shapes are extracted. The obtained results are contrasted with the bladed disks mode shapes, in order to validate the classification proposed. The simulated Kaplan runner is also experimentally studied. A numerical modal analysis is carried out in the real runner. Different, global and local, mode shapes are identified. The global mode shapes extracted by numerical and experimental modal analysis are compared and discussed. Finally, the local mode shapes identified are commented and explained by means of numerical simulation.
... Modal analysis is one of the most commonly used methods to study the dynamic characters of structures. Huang et al. [2] studied the dynamic characters of pump turbine runner from the perspective of structural shapes. The natural modes of different sizes of bladedisk structures were measured by experiment and numerical simulation, and the effects of blade shape and number were discussed in detail. ...
... Nodal Diameter (ND) and Nodal Circle (NC) refer to the straight or circumferential line where the displacement of the disc structure remains at zero during vibration, which can be used to describe the mode shapes of the runner [2]. The ND and NC modes in this paper refer to axial vibration in particular. ...
It is currently in the period of high-speed construction of pumped storage projects. However, the problems caused by vibration of pump turbine units, especially the runners, are very serious. It is of great significance to study the dynamic characteristics of pump turbine runner for the safety and stability of power station. In this paper, the natural modes of a pump turbine runner in the air and in the flow channels are calculated by numerical method. The influence and mechanism of the outer edge modification on the natural frequencies of the runner are studied. The results show that, for the object studied in this paper, the frequency of most modes will be decreased by thickening the outer edge. The frequency change can be attributed to two aspects, one is the change of the mass and the stiffness of the runner, and the other is the change of added mass of the water. Furthermore, the main mechanism of outer edge modification affecting the added mass coefficient is that the height of the radial clearance is changed.
... Finally, disk-blades-disk assemblies (Figure 1d), which are the type of structures analyzed in this paper, are present in closed centrifugal impellers (with working fluid air and water) and high head Francis runners, as seen in Figure 2. The several first mode shapes of these structures are dominated by the disk-part (blades are doubly clamped), which indicates mode shapes with deformation in the traverse direction to the disk plane [6,[26][27][28][29][30][31][32][33]. In the aforementioned references, the diametrical modes (modes with nodal diameters) are particularly considered, because they are [3], (b) Bladed disk structure [4], (c) Disk-blade assembly [5], and (d) Disk-blades-disk assembly [6]. ...
... Finally, disk-blades-disk assemblies (Figure 1d), which are the type of structures analyzed in this paper, are present in closed centrifugal impellers (with working fluid air and water) and high head Francis runners, as seen in Figure 2. The several first mode shapes of these structures are dominated by the disk-part (blades are doubly clamped), which indicates mode shapes with deformation in the traverse direction to the disk plane [6,[26][27][28][29][30][31][32][33]. In the aforementioned references, the diametrical modes (modes with nodal diameters) are particularly considered, because they are the lower modes in frequency and the most prone to be excited. ...
... The influence of clamping a disk-like structure, on the first diametrical modes with n ≥ 2, which are the first diametrical modes appearing disk-blade-disk structures, is almost negligible, especially for n > 2 [8]. Many references show that the first modes of a real disk-blade-disk configuration [6,[31][32][33]40] are dominated by disk-modes and therefore the effect of the clamping is also to slightly increase the first diametrical mode shapes without modifying the main characteristics of the mode shape, i.e., the aforementioned characteristics of the diametrical mode shapes are still the same. ...
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.
... The final objective is to identify the natural frequencies and the damping ratios of the runner, taking into account the added mass and damping of the surrounding water, because it has been demonstrated that these effects can considerably affect the results [14]. Moreover, additional boundary conditions such as the proximity of walls can also influence the added mass effects, which have been investigated from simple structures like disks [15] to actual prototype structures [16][17][18]. ...
... Several works devoted to investigating the modal behavior and dynamic responses of hydraulic turbine runners both in air and water can be found in the literature based on FEM and AFSCM [4][5][6][7][8][9][10][11][12][13][14][15]. In all cases, the numerical results have shown a good agreement with the corresponding measured ones, which fully validates the feasibility of FEM and AFSCM for the current study. ...
... The observed effects can be explained firstly by the size of the cavity and secondly by its location relative to the largest blade deformations for each mode shape. To quantify the effect of cavity size, the CSR defined by Equation (15) has been correlated to the FRRs in Figure 9 for the three modes. It can be clearly observed that the added mass effect decreases when the ratio increases. ...
To have a safe structural design, an analysis of the dynamic behavior of a Francis turbine runner with consideration of the added mass effects of surrounding water is necessary during design phase. Both in design and at off-design operations, large-scale forms of attached cavitation may appear on runner blades and can change the added mass effects of the surrounding fluid in relation to a single water domain. Consequently, a numerical investigation of the modal response of a Francis runner has been carried out by reproducing the presence of various sizes of leading edge cavitation (LEC) and trailing edge cavitation (TEC). The fluid–structure interaction problem has been solved by means of an acoustic-structural coupling method. The calculated added mass effects with cavitation have been compared with those corresponding to the pure water condition without cavitation. Firstly, a single blade has been investigated to evaluate the level of significance for the proposed cavity shapes and dimensions. Afterwards, based on the results obtained, the complete runner structure has been considered, factoring in similar cavity shapes and locations. The results prove that significant added mass effects are induced on the entire runner by the attached cavitation that increase the natural frequencies of the first modes. Moreover, the added mass effects increase with cavity size and amplitude of blade deformation below the cavity.
... The fluid density, the value of the speed of sound in the fluid medium and geometrical dimensions have to be considered in order to understand the effect of those parameters on the natural frequencies and mode-shapes. Due to the similarity on the mode-shapes between the disk and the more complex disk-like structures such as hydraulic runners Huang, 2011;Huang et al., 2013a;Liang et al., 2007;Presas et al., 2012;Tanaka, 2011), the dynamic response of disks has been deeply studied in the last years. ...
... FEM numerical models have been demonstrated in many works to correctly estimate the natural frequencies of submerged structures using acoustic elements for modelling the surrounding fluid (Escaler et al., 2017;Huang et al., 2013a;Liang et al., 2007;Liang and Wang, 2003;Rodriguez et al., 2012;Valentín et al., 2014). Furthermore, the acoustic natural frequencies of the fluid cavity can be also determined using this method (Graf et al., 2014). ...
