bluuebunny/crossref_metadata_2025 huggingface dataset:
Monte Carlo simulations of Upsilon meson production in p + p at

s

= 500 GeV
Authors: Bielcik Jaroslav , Ceska Jakub , Das Ayanabha , Kosarzewski Leszek , Myska Miroslav
Published: October 2022

Quarkonium production in proton-proton collisions serves as an essential baseline for studying the effect of quarkonium suppression in proton-nucleus and nucleus-nucleus collisions. This paper presents the main characteristics of Upsilon mesons production in proton-proton collisions at

s

=
500

GeV

studied with two Monte Carlo event generators: Pythia and Herwig and the results compared. Main aim of these simulations is to explore the dependence of normalised Upsilon meson yield on normalised event multiplicity and the influence of the feed-down effect on Upsilon meson production. The simulations show that the normalised Upsilon yield rises stronger than linear with regards to the normalised charged particle multiplicity. A mass ordering is found for Upsilons originating from feed-down and it suggests that the observed strong increase depends on the scale of the original hard process producing the quarkonium state.
Hyperfine structure studies of neutral praseodymium with Fourier transform spectroscopy
Authors: Wang Ting , Zheng Hongfeng , Geng Yidan , Yu Ziqing , Dai Zhenwen
Published: October 2022

The hyperfine structure patterns of some neutral praseodymium (Pr I) lines in the range of 2969 − 34998 cm−1 were investigated based on the archival data from the Fourier transform spectrometer at the US National Solar Observatory. The hyperfine magnetic dipole interaction constants A are presented by fitting the spectra with our spectral analysis program. The HFS constants A for 56 levels of Pr I from 0.0 to 27602.42 cm−1 were determined.
Revisiting the Affleck-Dine mechanism for primordial black hole formation
Authors: Kasai Kentaro , Kawasaki Masahiro , Murai Kai
Published: October 2022

We study a primordial black hole (PBH) formation scenario based on the Affleck-Dine (AD)
mechanism and investigate two PBH mass regions: M ∼ 30 M
⊙ motivated by the LIGO-Virgo
observations of the binary black hole mergers and M ≳ 104
M
⊙ motivated by the
observations of supermassive black holes at the center of galaxies. In the previous studies, it
has been considered that the inhomogeneous AD baryogenesis generates regions with a large baryon
asymmetry, some of which collapse into PBHs. In this paper, we show that this scenario is
severely constrained due to the baryon asymmetry remaining outside PBHs, which would spoil the
success of the big bang nucleosynthesis. Then, we propose an alternative scenario where the AD
leptogenesis results in the inhomogeneous formation of Q-balls with lepton charges, which collapse
into PBHs. As a result, we find that our scenario can explain the favorable PBH abundance without
conflicting with the observational constraints.
Generalized Regge-Wheeler equation from Effective Field Theory of black hole perturbations with a timelike scalar profile
Authors: Mukohyama Shinji , Takahashi Kazufumi , Yingcharoenrat Vicharit
Published: October 2022

Recently, the Effective Field Theory (EFT) of perturbations on an arbitrary background metric with a timelike scalar profile was formulated in the context of scalar-tensor theories. Here, we generalize the dictionary between the coefficients in the EFT action and those in covariant theories to accommodate shift- and reflection-symmetric quadratic higher-order scalar-tensor theories, including DHOST as well as U-DHOST. We then use the EFT action to study the dynamics of odd-parity perturbations on a static and spherically symmetric black hole background with a timelike scalar profile. Finally, we obtain the generalized Regge-Wheeler equation that can be used, e.g., to determine the spectrum of quasinormal modes and tidal Love numbers.
Painlevé analysis, auto-Bäcklund transformations, bilinear forms and soliton solutions for a (2+1)-dimensional variable-coefficient modified dispersive water-wave system in fluid mechanics
Authors: Liu Fei-Yan , Gao Yi-Tian
Published: October 2022

In this paper, we investigate a (2+1)-dimensional variable-coefficient modified dispersive water-wave system in fluid mechanics. We prove the Painlevé integrability for that system via the Painlevé analysis. We find some auto-Bäcklund transformations for that system via the truncated Painlevé expansions. Bilinear forms and N-soliton solutions are constructed, where N is a positive integer. We discuss the inelastic interactions, elastic interactions and soliton resonances for the two solitons. We also graphically demonstrate that the velocities of the solitons are affected by the variable coefficient of that system.
Multi-band polarization switch based on magnetic fluid filled dual-core photonic crystal fiber
Authors: Zhang Lianzhen , Zhang Xuedian , Yu Xiantong , Liu Xuejing , Zhou Jun , Chang Min , Yang Na , Du Jia
Published: October 2022

The research of high-performance polarization controllers is of great significance for expanding the application field of polarization optics. Here, a polarization switch is demonstrated by using a dual-core photonic crystal fiber (DCPCF) with four symmetrical air holes, placed above and below each core, filled with magnetic fluid (MF). The switch, which utilizes a magnetic field to change the coupling length ratio of the x and y polarization modes, enables dynamic tuning of the polarization state and extinction ratio. Numerical results show that when the working length is 36.638 mm, the magneto–optical polarization switch can operate in four communication bands, i.e., 1509 nm to 1520 nm, 1544 nm to 1556 nm, 1578 nm to 1591 nm, and 1611 nm to 1624 nm. Moreover, the extinction ratio (ER) is greater than 20 dB in the fiber length range of 38.5 mm to 38.7 mm, indicating that the device has a good fault tolerance for the interception of the fiber length.
Oxidation behavior of Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2C-Mx
C (M = Ti, Zr, Hf, Nb, Ta) composite ceramic at high temperature
Authors: Xu Shuai , Wang Tao , Wang Xingang , Wu Lu , Fang Zhongqiang , Ge Fangfang , Meng Xuan , Liao Qing , Wei Jinchun , Li Bingsheng
Published: October 2022

Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2C–Mx
C composite ceramic was prepared by hot press sintering, with the Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2C high-entropy carbide as the main phase. Secondary phase Mx
C (M = Ti, Zr, Hf, Nb, Ta) was found to be distributed relatively uniform in the composite ceramic. The oxidation behavior of the ceramic was examined after exposure to 923 K and 1173 K. Morphology of the surface and cross sections of all oxidation samples were observed. The characteristics of the oxidation behavior of the high-entropy carbide and the secondary phase Mx
C were compared and analyzed. The secondary phases (such as Ti-rich carbide or Hf-rich carbide) in the material were seriously oxidized at 923 K and 1173 K, which reflects the superior oxidation performance of the high-entropy carbide. The nano high-entropy oxides with Ti, Zr, Hf, Nb, Ta, and O elements were discovered by oxidation of the composite ceramic. This research will help deepen the understanding of the oxidation mechanism of high-entropy carbide and composite ceramic.
High efficiency of Brillouin scattering behavior in single-mode Ge–As–Se–Te fibers at 2 μm
Authors: Fu Yue , Dai Shi-Xun , Xu Lu-Lu , Fang Yao-Jun , Wang Ying-Ying , Jiao Kai , Wang Xun-Si
Published: October 2022

The Brillouin characteristics of step-index Ge–As–Se–Te (GAST) fibers at 2 μm are designed and simulated on the basis of optical and acoustic properties. The refractive indexes of Ge20As20Se45Te15 glass and Ge20As20Se43Te17 glass serving as fiber core and cladding are 3.20 and 3.18 at 2 μm, and their acoustic velocities are 2200 m/s and 2300 m/s, respectively. Numerical results indicate that the stimulated Brillouin scattering (SBS) efficiency is 248 m−1⋅W−1, and the Brillouin threshold power is 66 mW when the core diameter of the 2-m-long GAST fiber is 4 μm at 2-μm wavelength. The optic–acoustic coupling factor, the Brillouin frequency shift, and the Brillouin gain coefficient are 0.98, 7.02 GHz, and 3.81 × 10−9 m/W, respectively. The SBS effect of GAST fibers simulated for the first time provides a new promising approach to selecting gain medium based on 2-μm-wavelength fiber laser.
Modelling the differential effects of age on transcranial magnetic stimulation induced electric fields
Authors: Alawi Mansour , Lee Poh Foong , Deng Zhi-De , Goh Yong Kheng , Croarkin Paul E
Published: October 2022

Objective. The therapeutic application of noninvasive brain stimulation modalities such as transcranial magnetic stimulation (TMS) has expanded in terms of indications and patient populations. Often neurodevelopmental and neurodegenerative changes are not considered in research studies and clinical applications. This study sought to examine TMS dosing across time points in the life cycle. Approach. TMS induced electric fields with a figure-of-eight coil was simulated at left dorsolateral prefrontal cortex regions and taken in vertex as a control region. Realistic magnetic resonance imaging-based head models (N = 48) were concurrently examined in a cross-sectional study of three different age groups (children, adults, and elderlies). Main results. Age had a negative correlation with electric field peaks in white matter, grey matter and cerebrospinal fluid (P < 0.001). Notably, the electric field map in children displayed the widest cortical surface spread of TMS induced electric fields. Significance. Age-related anatomical geometry beneath the coil stimulation site had a significant impact on the TMS induced electric fields for different age groups. Safety considerations for TMS applications and protocols in children are warranted based on the present electric field findings.
Vascular remodeling in sheep implanted with endovascular neural interface
Authors: John Sam E , Donegan Sam , Scordas Theodore C , Qi Weijie , Sharma Prayshita , Liyanage Kishan , Wilson Stefan , Birchall Ian , Ooi Andrew , Oxley Thomas J , May Clive N , Grayden David B , Opie Nicholas L
Published: October 2022

Objective. The aim of this work was to assess vascular remodeling after the placement of an endovascular neural interface (ENI) in the superior sagittal sinus (SSS) of sheep. We also assessed the efficacy of neural recording using an ENI. Approach. The study used histological analysis to assess the composition of the foreign body response. Micro-CT images were analyzed to assess the profiles of the foreign body response and create a model of a blood vessel. Computational fluid dynamic modeling was performed on a reconstructed blood vessel to evaluate the blood flow within the vessel. Recording of brain activity in sheep was used to evaluate efficacy of neural recordings. Main results. Histological analysis showed accumulated extracellular matrix material in and around the implanted ENI. The extracellular matrix contained numerous macrophages, foreign body giant cells, and new vascular channels lined by endothelium. Image analysis of CT slices demonstrated an uneven narrowing of the SSS lumen proportional to the stent material within the blood vessel. However, the foreign body response did not occlude blood flow. The ENI was able to record epileptiform spiking activity with distinct spike morphologies. Significance. This is the first study to show high-resolution tissue profiles, the histological response to an implanted ENI and blood flow dynamic modeling based on blood vessels implanted with an ENI. The results from this study can be used to guide surgical planning and future ENI designs; stent oversizing parameters to blood vessel diameter should be considered to minimize detrimental vascular remodeling.
Addressing transcranial electrical stimulation variability through prospective individualized dosing of electric field strength in 300 participants across two samples: the 2-SPED approach
Authors: Van Hoornweder Sybren , A Caulfield Kevin , Nitsche Michael , Thielscher Axel , L J Meesen Raf
Published: October 2022

Objective. Transcranial electrical stimulation (tES) is a promising method for modulating brain activity and excitability with variable results to date. To minimize electric (E-)field strength variability, we introduce the 2-sample prospective E-field dosing (2-SPED) approach, which uses E-field strengths induced by tES in a first population to individualize stimulation intensity in a second population. Approach. We performed E-field modeling of three common tES montages in 300 healthy younger adults. First, permutation analyses identified the sample size required to obtain a stable group average E-field in the primary motor cortex (M1), with stability being defined as the number of participants where all group-average E-field strengths ± standard deviation did not leave the population’s 5–95 percentile range. Second, this stable group average was used to individualize tES intensity in a second independent population (n = 100). The impact of individualized versus fixed intensity tES on E-field strength variability was analyzed. Main results. In the first population, stable group average E-field strengths (V/m) in M1 were achieved at 74–85 participants, depending on the tES montage. Individualizing the stimulation intensity (mA) in the second population resulted in uniform M1 E-field strength (all p < 0.001) and significantly diminished peak cortical E-field strength variability (all p < 0.01), across all montages. Significance. 2-SPED is a feasible way to prospectively induce more uniform E-field strengths in a region of interest. Future studies might apply 2-SPED to investigate whether decreased E-field strength variability also results in decreased physiological and behavioral variability in response to tES.
Comment on ‘The advanced tokamak path to a compact net electric fusion pilot plant’
Authors: Manheimer Wallace
Published: October 2022

This comment (letter) examines a recent GA concept which they hope will lead to a tokamak fusion pilot plant. As tokamaks are now the closest configuration to practical magnetic fusion, if they cannot do a pilot plant, almost certainly no other device can either. The conclusion is that constructing a tokamak fusion pilot plant at this time is enormously risky, and is almost certainly tremendous waste of scarce fusion resources, which could be better used on other efforts in the fusion effort.
Residual entropy of ice Ih by Wang–Landau Monte Carlo simulation of an effective Ising model
Authors: Li De-Zhang , Zhao Yu-Jun , Yang Xiao-Bao
Published: October 2022

Accurate evaluation of the residual entropy of three-dimensional ice systems remains a difficult task. In this work, we estimate the residual entropy of ice Ih (ordinary ice) by an improvement of the Wang–Landau Monte Carlo algorithm, which directly calculates the density of states of the system. We define an effective three-dimensional Ising model with nearest-neighbour interactions, and introduce the mapping of the spin configurations of this Ising model into the hydrogen configurations of ice Ih. The ground states of this Ising model are equivalent with the hydrogen configurations obeying the ice rules, therefore the ground state degeneracy directly determines the residual entropy. Our estimate is in good agreement with the famous theoretical approximation by Nagle in 1966, and other results evaluated from various methods. The advantage of making use of the equivalent Ising model is discussed. It is convenient to extend our approach to other lattice systems.
31st IAHR Symposium on Hydraulic Machinery and Systems
Authors: Trivedi Chirag
Published: October 2022

Hydropower is one of leading sources of energy used to meet the primary, secondary and territory ancillary services to balance the energy demand. Hydraulic turbine is essential component of a hydro power plant to generate electricity. The IAHR symposium on hydraulic machinery and systems provides unique opportunity to the academic and industrial research teams to exchange the stat-of-the-art knowledge and ideas on the development of the next-generation of hydropower technology. 31st Symposium on Hydraulic Machinery and Systems was organized by Norwegian University of Science and Technology, Trondheim, Norway, during 26 June – 01 July 2022. This preface describes the overall summary of the symposium, including the parallel sessions, scientific and cultural tours. For more specific detail, please visit the symposium website www.ntnu.edu/iahr2022. Scientific manuscripts reviewed by the experts, accepted and presented during the symposium are published in a proceeding at IOP Science EES conference series.
Experimental complex flow patterns in the pump intake with a low water level
Authors: Guo M , Tang X L , Li X Q
Published: October 2022

The present paper is an extension of the authors’ previous work [1], and the goal is to analyze and reveal the complex flow patterns in the pump intake with a low water level (lower than the critical water level) through PIV Technology (Particle Image Velocimetry). The results show that: the lower the water level (a) the geometric scale of the free-surface vortices increases, which potentially leads to pulling more air into the pipe system and the pump units of the pump station; (b) the sidewall-attached vortices have a larger geometric scale; (c) more backwall- and floor-attached vortices are captured, and their geometric scale is large. In brief, the experimental data of the paper indicate that the free-surface, backwall-, and floor-attached vortices are the main characters of the pump intake with a low water level. In engineering, the vortex suppression/eliminating devices in the vicinity of these locations should be emphasized.
Hydraulic geometric optimization on stagnating flow at the inlet of main pipe of underground pumping station
Authors: Guo M , Yao K W , Zhang S H
Published: October 2022

The underground pumping station is widely used in many important fields. However, the stagnating flow caused by the sharp geometric gradient at the interface between the primary pump intake and the main pipeline not only causes the performance deteriorations of the whole pump station but also leads to safety and operational stability challenges. In this paper, the numerical model of the related hydraulic phenomena is presented, moreover, the effectiveness and accuracy of the numerical model are verified by comparing it with the experimental results. The simulation results indicate that the hydraulic geometry optimization scheme at the inlet of the main pipe with 0.10 D (inner diameter of the main pipe) local rounding contributes the best effect on the hydraulic efficiency and operation stability of underground pump stations. The results may give a reference for the design of underground pump stations and the optimization of hydraulic geometry in related fields.
Experimental Investigation of a Free Runner Concept Downstream of Francis Turbines
Authors: Bosioc A I , Szakal R , Tanasa C , Susan-Resiga R.F.
Published: October 2022

The main purpose of the paper is to investigate experimentally a new concept by using a free runner downstream of the main hydraulic runner turbine to increase the flexibility in operation. The free runner concept supposes that rotates at the runaway speed with vanishing mechanical torque. The main purpose is to redistribute between the shaft and the periphery the total pressure and the moment of momentum, such that the flux of total pressure and the moment of momentum are not altered. Moreover, the free runner does not modify the operating point of the main hydraulic turbine runner. The experimental investigation focuses on velocity profiles measurements with the LDV system and the unsteady pressure measurements downstream the free runner, in the draft tube cone.
Intermittent cavitating flow field in tandem cascades of Kaplan turbines
Authors: Susan-Resiga R F , Ciocan T , Stuparu A , Gherghe G G
Published: October 2022

Within the framework of the classical turbine design setup, we present a numerical investigation of unsteady cavitating flow in tandem cascades of guide vanes and rotor blades. The practical relevance of the present investigation is ensured by choosing real blade profiles and domain geometry for the large Kaplan turbines (9.5 m rotor diameter) from the Iron Gates I hydropower plant on the Danube River. The 2D tandem cascade setup is obtained with a conformal mapping of the circular guide vane cascade into a straight cascade, while the rotor blade cascade is by default a straight one for axial turbines. Both single-phase and two-phase cavitating flows results are presented and analysed. The single-phase liquid flow displays rather modest pressure and tangential force fluctuations, with the characteristic blade passing frequency, due to the interaction of the rotor blades with the wakes of guide vanes. The two-phase cavitating flow displays a completely different dynamics in comparison to the liquid flow, with periodic cavitation growth and collapse at a specific frequency lower than the blade-passing one. Moreover, the tangential force on the rotor blade displays severe intermittency and the force fluctuations are almost one order of magnitude larger than in the single-phase flow.
Numerical study on effect of operating condition and solid concentration on hydro-abrasive erosion of high head Francis turbine
Authors: Sharma S , Sharma S R , Gandhi B K
Published: October 2022

The powerplants in the Himalayan region are generally subjected to hydro-abrasive erosion. The deterioration of components due to erosion causes reduction in performance, changes the fluid flow pattern and even the breakdown of the turbine. In the present work, the Bhilangana-III powerplant Francis turbine is considered a reference turbine for numerical investigation using the computational fluid dynamics (CFD) tool. The study presented an evaluation of hydro-abrasive erosion of high head Francis turbine for the different operating conditions and sediment concentrations. The modified Grant and Tabakoff erosion model is used for the erosion rate calculation. To investigate the effect of various operating conditions, the study is conducted at part load, best efficiency point (BEP) and high load. Also, to examine the impact of suspended sediment on the erosion of turbine components, the solid concentration varies from 500, 1200, 2000, 3000 and 4000 ppm. The observed erosion pattern is similar at all operating conditions for the stay vane, guide vane and runner, but the density of erosion is different. The observed deterioration density due to erosion is higher for part and full load than in the BEP condition. The guide vanes and runner vanes are highly susceptible to erosion due to higher absolute velocity and relative velocity at guide vane and runner vane, respectively. The observed erosion rate variation is qualitatively in-line with the on-field turbine erosion condition. It is also found that the increase in erosion rate with the sediment concentration is almost linear but more than 90% and 79% higher for the runner than stay vane and guide vane, respectively.
Characterization of the hydrodynamic instabilities in a pump-turbine operating at part load in turbine mode
Authors: Cavazzini G , Zanetti G , Santolin A , Ardizzon G
Published: October 2022

Pump-turbines (RPT) nowadays represents the most common mechanical equipment adopted in the new generation of storage hydro plant. In order to balance the frequent changes in electricity production and consumption caused by unpredictable renewable energy sources, RPT are forced to rapidly switch between the pumping and generating mode also extending their operation under off-design conditions in unstable operating areas. Because of the design criterion adopted for the development of a RPT, an unstable behavior represented by a typical S-shaped profile with a positive slope in the machine’s characteristic can occur near to the runaway condition.

With the purpose of evaluating the evolution of the fluid field near to the no-load condition, an in-depth CFD analysis of the RPT model test of the Norwegian Hydropower Center is performed by retracing the machine’s characteristic curve running through the flow-speed characteristic curve up to the turbine brake region for fixed guide vanes opening. To validate the numerical results, a comparison with the experimental results in terms of characteristic curves and pressure signals is performed.

The results allow to capture the 3D characteristics of the unsteady phenomena, progressively evolving in an organized rotating stall, highlighting also the influence of the flow rate change from partial loads to the turbine brake operation on their development. In order to characterize the pulsating nature of the instability phenomena developing in the runner and in the rotor-stator interaction, a time-frequency analysis is performed on the numeric pressure and torque signals. The combination between fluid-dynamic and time-frequency analysis makes it possible to identify and characterize three evolution phases: inception, growth and consolidation.
Experimental Investigation of Flow Inside the Back-Sidewall Gaps of Centrifugal Pump and its Impact on Axial Thrust
Authors: Zemanová L , Rudolf P , Zubík P
Published: October 2022

Despite the sidewall gaps of centrifugal pumps are tiny narrow spaces, the flow inside them can have a great impact on the flow field in the whole machine. Regardless of its influence, there is no full understanding of the flow in those regions. A theory exists for the simplified cylindrical cavity with a rotating disk, whose application to real hydraulic machines is questionable. To investigate the flow in the sidewall gaps of centrifugal pumps, a test rig including a real impeller has been built up. It enables observation of the flow in the back-sidewall gap by optical methods and evaluation of axial thrust and torque. The measurements were performed for a range of rotational speeds in order to map possible flow regimes and patterns. It was found out, that the basic theory and map of the flow regimes obtained for a simple rotating cavity is inapplicable for the back-sidewall gaps of real hydraulic machines. The flow field is significantly influenced by the impeller blades, and consequently, the map of the regimes is shifted compared to the one derived for the simple cylindrical cavity with a rotating disk. The discrepancies were described and a new map of flow regimes was introduced.
Investigation on hydrodynamic characteristics of a hydrofoil based on γ-Reθt
transition model
Authors: Ye Changliang , Wang Fujun , Zheng Yuan , Zhou Daqing , Van Esch B P M
Published: October 2022

The complex flow field caused by the dynamic stall can affect the operational stability of hydrodynamic machinery. In this paper, the NACA0009 blunt trailing edge hydrofoil is used as the object of study, and the dynamic stall characteristics of the hydrofoil are investigated by using the transition model and the dynamic mesh method. It is found that the hydrofoil deep stall calculated by the transition model is delayed compared to that calculated without the transition model. The hydrofoil dynamic stall can be divided into four stages, initial stage, development stage, stall inception stage and deep stall stage. In the initial stage and the development stage, the lift and drag characteristics are influenced by the shedding vortex. In the stall inception stage and the deep stall stage, the lift and drag characteristics are influenced by the leading edge separation vortex and the trailing edge vortex. The increase of angular velocity and Reynolds number of the dynamic hydrofoil delay the onset of the deep stall while accelerating the boundary layer transition. The research in this paper has a certain guiding effect for the safe and stable operation of hydrodynamic machinery.
Simulation of pressure pulsations for pumped-storage units with wide operating range and comparison to experiments
Authors: Magnoli M.V. , Necker J.
Published: October 2022

The diversity of energy conversion sources in the current energy market increases the demand for stabilizing the electrical grid through ancillary services, frequency and power regulation from the facilities. Pumped-storage units with reversible pump-turbines or ternary sets constitute the currently most advanced solution for providing these services. This implies that pumped-storage units are required to operate in larger head and power ranges than before. In order to increase their flexibility in pump mode, variable speed units have been applied more frequently with additional challenges for the operating range in pump mode.

The extension of the operating flexibility in pump mode makes use of a large portion of the model pump characteristic curve, especially in the case of variable speed units. Important challenges to the hydraulic development are among others the cavitation behaviour, hydraulic stability and pressure pulsation level. This study concentrates on the pressure pulsations in pump mode, which are of great relevance for the machine smooth operation.

The pressure pulsations in a regulated radial reversible pump-turbine with low specific speed are numerically simulated with computational fluid dynamics (CFD) for several points along the complete operating range of the pump characteristic curve. The finite volume model includes the complete hydraulic machine from draft tube to spiral case and hybrid turbulence models were used, in this case scale adaptive simulation (SAS). The numerical simulation offers the possibility to assess different flow quantities at any point of the finite volume model, providing additional data to the experimental model test results.

The integral quantities, e.g. head, flow and efficiency, were compared to the model test results to validate the numerical model. The simulated pressure pulsation amplitude and frequency were also compared to the measured pressure pulsations at the model at the available measuring locations in the spiral case, vaneless space and draft tube cone. After the validation, the computed flow fields were used to derive the pressure pulsation amplitude at other machine locations and components, e.g. at the runner.
Numerical investigation of the impact of cavitation on the pressure fluctuations in a Francis turbine at deep part load conditions
Authors: Wack J , Grübel M , Conrad P , Von Locquenghien F , Jester-Zürker R , Riedelbauch S
Published: October 2022

Hydropower plants can play an important role to stabilize the electrical grid when the share of volatile renewable energies increases. This goes hand in hand with a more flexible operation of the turbines and longer operation in off-design operating points. The increased pressure fluctuations that occur at off-design conditions may reduce the lifetime of the turbines. Consequently, this should be considered within the design process to develop efficient but also robust turbines. To derive suitable simulation setups that can be used in the design process, it is crucial to have a deep understanding of specific flow phenomena. As pressure fluctuations are of main importance in terms of fatigue, it is important that simulations can capture them well. Within this study, a deep part load operating point of a Francis turbine at model scale is investigated. By using three different meshes the influence of mesh refinement on the predicted pressure fluctuations is analyzed. Furthermore, by means of single- and two-phase simulations it is investigated how the pressure fluctuations are affected by the occurrence of cavitation. The results show only minor differences between the different meshes, whereas significant differences are observed between a single- and two-phase treatment.
How angular-momentum flux controls Francis turbine full-load surge
Authors: Dörfler P K , Wack J , Riedelbauch S
Published: October 2022

Hydropower plants equipped with Francis turbines may enter unstable conditions at high turbine discharge [13], with strong pulsations of power output and internal pressure. The cause are oscillations of a vapor-filled cavity in the vortex flow downstream of the turbine runner, interacting with the draft tube and penstock pressure. The paper describes the structure and simulation results of a 1D distributed-parameter model for full-load surge, parametrized from results of a high-resolution unsteady two-phase CFD simulation study (Wack [14]) of high-load pulsations in the reduced-scale model of a medium-specific speed Francis turbine. In earlier research on the same model turbine, Müller [12] had suggested that runner blade cavitation could cause instability. To clarify this, variation of turbine intake flow was sup-pressed, and the influence of pressure variation via runner blade cavitation on the relative runner exit flow angle and angular-momentum flux was simulated. Due to the upstream boundary condition, the influence of mass-flow gain χ is replaced by a cavitation gain factor ψ, likewise delayed by the limited speed of swirl propagation. It is found that gain factors obtained from steady-state simulation cannot be directly used with a lumped-parameter model because the swirl effect is much reduced due to its phase changes along the vortex; using the steady-state gain factors would thus exaggerate the influence of swirl on cavity volume. Simulation in frequency domain with realistic swirl transport delay confirms that instability can occur because in some parts of the cavitation zone the swirl provides oscillation power.
Identification of the precessing vortex core in a hydro turbine model using local stability analysis and stochastic modeling
Authors: Litvinov Ivan , Sieber Moritz , Oberleithner Kilian
Published: October 2022

Stochastic modeling and local linear stability analysis (LSA) is employed to predict the onset of the precessing vortex core (PVC) in the hydro turbine model. The method of the stochastic modeling based on the pressure fluctuation signals correctly predicts the instability of the azimuthal mode m = 1 at flow rates below 0.7Q

c
. This is in line with local LSA that shows that the azimuthal modes m = 1 and m = 2 are absolutely unstable below the flow rate of 0.7Q

c
. The absolute instability of mode m = 2 is a new observation in the part load regimes of hydro turbines and plays a significant role in the dynamics of the PVC. As demonstrated in this paper, local LSA and stochastic modelling are both methods to uncover the driver of the PVC using sparse experimental data stemming from either spatially resolved but non-timeresolved PIV snapshots or single-point time-resolved wall pressure recordings, respectively. This makes these methods suitable to be applied to configurations of industrial relevance.
On the existence of adverse pressure gradient in decelerated swirling flow and its suppression by water jet injection
Authors: Urban Ondřej , Rudolf Pavel
Published: October 2022

The paper revisits the theory originally published by Hall that explains the presence of adverse pressure gradient at the axis of a diffuser with swirling flow. It presents the fields of the axial pressure derivative obtained by CFD simulations of flow in a swirl generator, which support the theory. The last part brings cautionary results regarding the suppression of the backflow caused by this adverse pressure gradient by water jet injection. On a case with a strong swirl intensity leading to a strong vortex rope, it is shown that the injected jet may be deflected to the outer walls and rotate with the outer swirling flow, eventually leading to stronger pressure pulsations than in the original state. Further investigation shows that high enough diameter of the jet is needed to ensure its stability.
Measurement of sediment particle size distribution and shape using dynamic imaging analysis
Authors: Arora N , Kumar A , Singal S K
Published: October 2022

Hydropower plants operating in fragile mountainous regions face severe sediment erosion of hydraulic turbines, resulting in decreased efficiency, frequent power interruptions, and downtime for maintenance. The sediment size and shape are detrimental to the hydraulic turbines and influence sediment erosion. Sediment management is a crucial aspect of tackling sediment erosion in hydraulic turbines. The traditional method of measuring particle size and shape is time-consuming, labour-intensive, and usually requires statistical analysis. The present study applies the recent technique of dynamic imaging analysis to determine the particle size distribution and shape of sediment. Five different silt-sand mixtures have been used to check the ability of dynamic imaging analysis. Further, the repeatability and reliability of the results were checked by carrying out five repeated measurements of each sample under the same condition in a short period of time. This study will help the researchers and sedimentologists to adopt the dynamic imaging analysis technique for measuring particle size and shape and help the instrument developer in designing a better future version of the instrument.
Problem Identification and Condition Monitoring status of Nepalese Power Plants
Authors: Sapkota P , Chitrakar S , Neopane H P , Thapa B
Published: October 2022

Condition monitoring is the process of detecting faults in machine components with the help of measurement & analysis of pre identified parameters in a hydro power plant. This paper presents the different problems identified in the selected hydropower plants owned by Nepal Electricity Authority. The power plants have been selected on the basis of type of turbines and total power output. They include all types of turbines that has been in use in Nepal i.e., Pelton, Francis and Bulb turbines. Similarly, they have been selected in accordance to power output i.e., from 1 MW to 144 MW. The questionnaire has been developed and surveyed for the identification of problems in these hydropower plants as well as status of measurement devices. The paper presents the status of different measurement processes, instruments and sensors being used in the selected hydropower plants. The paper further presents possibly of condition monitoring and fault detection process that can be implied in these power plants.
Lattice Boltzmann simulation of the ERCOFTAC pump impeller
Authors: Roos Launchbury D , Casartelli E , Mangani L
Published: October 2022

The analysis of unsteady flows is becoming more and more important in the field of hydraulic turbomachinery applications, both for stable and especially for unstable operating conditions and other transient phenomena. Unsteady Reynolds-averaged Navier-Stokes (RANS) methods for incompressible flows, implemented via finite volume or finite element approaches, reach their limit in both accuracy and acceptable computational time. The accuracy mainly suffers due to the strong dependence of the solution on turbulence model variants. Furthermore, incompressibility of the flow and the linked implicit pressure equation makes large eddy simulations (LES) of Navier-Stokes-based methods for such flows prohibitively expensive. An alternative to Navier-Stokes fluid solvers are methods based on the solution of the discrete Boltzmann equation, so-called Lattice Boltzmann Methods (LBM). The purpose of this work is to present first results of an ongoing project involving the simulation of unsteady hydraulic turbomachines at high Reynolds numbers. For this purpose, the ERCOFTAC pump impeller was selected as a test case. Results obtained with the current implementation of the in-house code suggest, that the present methodology could provide a viable alternative for the analysis of unsteady flow phenomena in hydromachines.
Multidisciplinary optimization of a Francis turbine runner
Authors: Tengs E , Charrassier F , Jordal M , Iliev I
Published: October 2022

A fully automated multi-disciplinary design optimization procedure for a Francis turbine runner has been developed in a previous task of the Horizon2020-HydroFlex project. The design optimization was limited to blade design, with the goal of improving the hydraulic efficiency and torque, and reducing the harmonic structural stresses. This is to ensure that the turbine is less prone to fatigue, but still performs well hydraulically. Results from the numerical optimization are presented in this paper. From the design optimization, two runner designs are highlighted. One that performs significantly better than a reference design, and one that performs significantly worse. It is observed that small, but significant improvements can be obtained in both torque and efficiency, while at the same time reducing the structural stresses drastically. This shows that there might be previously unknown areas in the design space that can be explored, especially on the structural side.
Numerical simulation of transient processes for pumped-storage power station with fixed and variable speed units
Authors: Cao R , Guo W C , Liu Y , Wu F L , Bai Q J
Published: October 2022

The pumped-storage power stations (PSPSs) with variable speed units (VSUs) have been emerging in recent years, and the research on the transient processes of those PSPSs is of great significance. In this paper, the transient processes of a PSPS with four units, i.e. three fixed speed units (FSUs) and one VSU, sharing one tunnel are numerically simulated under the conditions of large fluctuation and small fluctuation. Firstly, combining the calculation method of hydraulic transient processes and the basic equations of pump turbine, doubly-fed induction motor (DFIM) and governor, a hydraulic-mechanical-electrical coupling model of PSPS is established. Secondly, the data of an actual PSPS is substituted into the model and the corresponding parameters are set. Then, the transient processes of typical conditions of large fluctuation and small fluctuation are simulated respectively. Finally, according to the numerical simulation results, the characteristics of the transient processes of PSPS with three FSUs and one VSU are analyzed. The results show that, under large fluctuation conditions, whether the initial operating states of FSUs and VSU are consistent or not, the transient processes are similar. Under small fluctuation conditions, the VSU can adjust the active power to meet the grid demand more quickly than the FSUs.
Optimization of guide vanes for variable speed Francis turbines – Human controlled vs. automated approach
Authors: Stojkovski Filip , Markov Zoran
Published: October 2022

Guide vanes of hydraulic turbines can maximise turbine efficiency and directly influence on turbine operating characteristics. A hydraulic analysis is carried out on geometrically parameterised guide vane foils, to maximise efficiency and potentially observe which configuration gives operating range expansion. Variable-speed operated turbines in hydropower plants tend to run with improved performance at off-design operating points due to the speed variations. A combination of variable speed turbine operation and guide vane shape optimization gives a win-win situation in water to energy usage ratio. Human controlled developed designs and CFD calculations were previously done. The obtained results are compared with automated approach in ANSYS Workbench using Design of Experiments. The numerical tests were made on parametrically developed guide vane cascades, where the turbine efficiency is the evaluated parameter and it is observed in the range of several rotational speeds and calculated flow rates. The cascade design which produces less turbine efficiency deviations for the tested rotational speed range is later exported and hydraulically and geometrically compared with the developed design from the manual approach. The tested configurations of the guide vanes are developed on the basis of Francis 99 turbine model from the Waterpower Laboratory at the Norwegian University of Science and Technology in the existing geometric space for the guide vanes and blades axis positioning circumference.
An engineering approach for the prediction of fatigue damage in the part load regime
Authors: Von Locquenghien F , Leibing B
Published: October 2022

Due to the volatile electricity received from solar and wind power plants, the energy market requires highly variable hydropower machines which are able to cope with fast changes of their operating regimes. With the need for flexible operation, Francis runners are exposed to various operating conditions outside the traditional operating range. Hence, the runners must be specifically designed for long time part load operation to meet hydraulic and structural requirements. Therefore, it is inevitable to have a reliable but also practical engineering approach in the design phase of the projects in order to ensure sufficient fatigue life of the Francis runners. Deep part load operation mainly consists of stochastic loads acting on the runner blades. Previous publications show that it is reasonable to normalize the Rainflow matrix of stress amplitudes to represent the characteristic behaviour at deep part load operation. Hence, it is feasible to utilize the normalized Rainflow matrix to predict the fatigue damage of Francis runner designs without prototype measurements. Within this paper, a scaling method to derive project specific fatigue results for deep part load is introduced and subsequently validated through an intercomparison of available strain gauge measurement data and prediction. Based on the results, the accuracy of the proposed engineering approach and possible impacts of different boundary conditions are discussed.
Corrosion fatigue investigations on cast, forged and welded nickel-martensitic steels for hydro turbines
Authors: Leibing B , Von Locquenghien F , Rückle D , Schellenberg G
Published: October 2022

Facing an increased demand for flexible operation of hydro power plants (HPPs), Francis runners are substantially subjected to operating conditions beyond the traditional operating ranges. In order to ensure a reliable service of major HPP components covering their complete service life, a fundamental understanding of both load and material fatigue behavior is essential. Due to the cyclic loading in water, reliable corrosion fatigue data is required for the runner fatigue assessments. In previous publications, a state-of-the-art corrosion fatigue testing campaign within a collaborative German research project was described and results for a common cast steel used for the manufacturing of hydro runners were presented. The material testing program for the 13 % Chromium and 4 % Nickel steel has advanced since then and important aspects beyond varying water qualities and different stress ratios have been investigated. Within this conference contribution, corrosion fatigue investigations that were carried out on cast, forged and welded nickel-martensitic steels are described and recently gained results are presented.
PZT actuators as on-board instruments to reduce vibrations and strains in submerged structures
Authors: Sánchez-Botello X , De La Torre O , Roig R , Costa-Castelló R , Escaler X
Published: October 2022

This paper presents the design and evaluation of an active control system to reduce vibrations and strains of submerged structures. For that, a metallic disk mounted in a test rig has been equipped with on-board waterproof strain gauges and accelerometers, to measure its structural response, and with an on-board PZT actuator patch, to provide the required control force. This control force is computed in real-time by an optimal algorithm that determines the exact voltage to be supplied to the PZT patch in order to mitigate any increase of vibrations and/or strains detected by the sensors. In order to capture the dynamics of the structure when it is excited both in air and submerged in water, a plant model has been identified from the Frequency Response Functions (FRFs) obtained experimentally from the measured vibrations and numerically from simulated strains. With these plant models, two different control techniques based on a Linear Quadratic Gaussian (LQG) controller and on an H

∞
controller have been implemented and simulated under different types of excitations. The obtained results are satisfactory and support the need to continue the research to validate them experimentally.