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3D Casing-Distributor Analysis for Hydraulic Design Application
Devals, Christophe,Zhang, Ying,Dompierre, Julien,Vu, Thi C.,Mangani, Luca,Guibault, Francois Korean Society for Fluid machinery 2015 International journal of fluid machinery and syste Vol.8 No.3
Nowadays, computational fluid dynamics is commonly used by design engineers to evaluate and compare losses in hydraulic components as it is less expensive and less time consuming than model tests. For that purpose, an automatic tool for casing and distributor analysis will be presented in this paper. An in-house mesh generator and a Reynolds Averaged Navier-Stokes equation solver using the standard $k-{\omega}$ shear stress transport (SST) turbulence model will be used to perform all computations. Two solvers based on the C++ OpenFOAM library will be used and compared to a commercial solver. The performance of the new fully coupled block solver developed by the University of Lucerne and Andritz will be compared to the standard 1.6ext segregated simpleFoam solver and to a commercial solver. In this study, relative comparisons of different geometries of casing and distributor will be performed. The present study is thus aimed at validating the block solver and the tool chain and providing design engineers with a faster and more reliable analysis tool that can be integrated into their design process.
3D Casing-Distributor Analysis for Hydraulic Design Application
François Guibault,Christophe Devals,Ying Zhang,Julien Dompierre,Thi C Vu,Luca Mangani 한국유체기계학회 2015 International journal of fluid machinery and syste Vol.8 No.3
Nowadays, computational fluid dynamics is commonly used by design engineers to evaluate and compare losses in hydraulic components as it is less expensive and less time consuming than model tests. For that purpose, an automatic tool for casing and distributor analysis will be presented in this paper. An in-house mesh generator and a Reynolds Averaged Navier-Stokes equation solver using the standard k-ω shear stress transport (SST) turbulence model will be used to perform all computations. Two solvers based on the C++ OpenFOAM library will be used and compared to a commercial solver. The performance of the new fully coupled block solver developed by the University of Lucerne and Andritz will be compared to the standard 1.6ext segregated simpleFoam solver and to a commercial solver. In this study, relative comparisons of different geometries of casing and distributor will be performed. The present study is thus aimed at validating the block solver and the tool chain and providing design engineers with a faster and more reliable analysis tool that can be integrated into their design process.
Steady and unsteady flow computation in an elbow draft tube with experimental validation
Vu, Thi C.,Devals, Christophe,Zhang, Ying,Nennemann, Bernd,Guibault, Francois Korean Society for Fluid machinery 2011 International journal of fluid machinery and syste Vol.4 No.1
Steady state computations are routinely used by design engineers to evaluate and compare losses in hydraulic components. In the case of the draft tube diffuser, however, experiments have shown that while a significant number of operating conditions can adequately be evaluated using steady state computations, a few operating conditions require unsteady simulations to accurately evaluate losses. This paper presents a study that assesses the predictive capacity of a combination of steady and unsteady RANS numerical computations to predict draft tube losses over the complete range of operation of a Francis turbine. For the prediction of the draft tube performance using k-${\varepsilon}$ turbulence model, a methodology has been proposed to average global performance indicators of steady flow computations such as the pressure recovery factor over an adequate number of periods to obtain correct results. The methodology will be validated using two distinct flow solvers, CFX and OpenFOAM, and through a systematic comparison with experimental results obtained on the FLINDT model draft tube.
Devals, Christophe,Vu, Thi C.,Guibault, Francois Korean Society for Fluid machinery 2015 International journal of fluid machinery and syste Vol.8 No.3
This paper presents a CFD-based methodology for the prediction of guide vane torque in hydraulic turbine distributor for aligned and misaligned configurations. A misaligned or desynchronized configuration occurs when the opening angle of one guide vane differs from the opening angle of all other guide vanes, which may lead to a torque increase on neighbouring guide vanes. A fully automated numerical procedure is presented, that automates computations for a complete range of operation of a 2D or 3D distributor. Results are validated against laboratory measurements.
François Guibault,Christophe Devals,Thi C. Vu 한국유체기계학회 2015 International journal of fluid machinery and syste Vol.8 No.3
This paper presents a CFD-based methodology for the prediction of guide vane torque in hydraulic turbine distributor for aligned and misaligned configurations. A misaligned or desynchronized configuration occurs when the opening angle of one guide vane differs from the opening angle of all other guide vanes, which may lead to a torque increase on neighbouring guide vanes. A fully automated numerical procedure is presented, that automates computations for a complete range of operation of a 2D or 3D distributor. Results are validated against laboratory measurements.
Bahrami, Salman,Tribes, Christophe,von Fellenberg, Sven,Vu, Thi C.,Guibault, Francois Korean Society for Fluid machinery 2015 International journal of fluid machinery and syste Vol.8 No.3
A robust multi-fidelity optimization methodology has been developed, focusing on efficiently handling industrial runner design of hydraulic Francis turbines. The computational task is split between low- and high-fidelity phases in order to properly balance the CFD cost and required accuracy in different design stages. In the low-fidelity phase, a physics-based surrogate optimization loop manages a large number of iterative optimization evaluations. Two derivative-free optimization methods use an inviscid flow solver as a physics-based surrogate to obtain the main characteristics of a good design in a relatively fast iterative process. The case study of a runner design for a low-head Francis turbine indicates advantages of integrating two derivative-free optimization algorithms with different local- and global search capabilities.
Validation of a CFD model for hydraulic seals
Roy, Vincent Le,Guibault, Francois,Vu, Thi C. Korean Society for Fluid machinery 2009 International journal of fluid machinery and syste Vol.2 No.4
Optimization of seal geometries can reduce significantly the energetic losses in a hydraulic seal [1], especially for high head runner turbine. In the optimization process, a reliable prediction of the losses is needed and CFD is often used. This paper presents numerical experiments to determine an adequate CFD model for straight, labyrinth and stepped hydraulic seals used in Francis runners. The computation is performed with a finite volume commercial CFD code with a RANS low Reynolds turbulence model. As numerical computations in small radial clearances of hydraulic seals are not often encountered in the literature, the numerical results are validated with experimental data on straight seals and labyrinth seals. As the validation is satisfactory enough, geometrical optimization of hydraulic seals using CFD will be studied in future works.
Salman Bahrami,Christophe Tribes,Sven von Fellenberg,Thi C Vu,François Guibault 한국유체기계학회 2015 International journal of fluid machinery and syste Vol.8 No.3
A robust multi-fidelity optimization methodology has been developed, focusing on efficiently handling industrial runner design of hydraulic Francis turbines. The computational task is split between low- and high-fidelity phases in order to properly balance the CFD cost and required accuracy in different design stages. In the low-fidelity phase, a physics-based surrogate optimization loop manages a large number of iterative optimization evaluations. Two derivative-free optimization methods use an inviscid flow solver as a physics-based surrogate to obtain the main characteristics of a good design in a relatively fast iterative process. The case study of a runner design for a low-head Francis turbine indicates advantages of integrating two derivative-free optimization algorithms with different local- and global search capabilities.
Circadian control of <i>ORE1</i> by PRR9 positively regulates leaf senescence in <i>Arabidopsis</i>
Kim, Hyunmin,Kim, Hyo Jung,Vu, Quy Thi,Jung, Sukjoon,McClung, C. Robertson,Hong, Sunghyun,Nam, Hong Gil National Academy of Sciences 2018 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.115 No.33
<▼1><P><B>Significance</B></P><P>The circadian clock is involved in aging in animals, where mutations in core clock genes accelerate aging. However, little is known about the relationship between aging and the circadian clock in plants. Using the well-studied process of leaf senescence in <I>Arabidopsis</I>, a higher plant, as a model for aging, we show that the circadian clock has a critical role in regulating the aging process in plants. Specifically, we show that PSEUDO-RESPONSE REGULATOR 9 (PRR9), a core clock component, positively regulates leaf senescence. <I>ORESARA 1</I> (<I>ORE1</I>), an aging regulator, is controlled by PRR9 via direct transcriptional activation and indirectly by suppressing <I>miR164</I>, a posttranscriptional repressor of <I>ORE1</I>, thus forming a coherent feed-forward regulatory loop.</P></▼1><▼2><P>The circadian clock coordinates the daily cyclic rhythm of numerous biological processes by regulating a large portion of the transcriptome. In animals, the circadian clock is involved in aging and senescence, and circadian disruption by mutations in clock genes frequently accelerates aging. Conversely, aging alters circadian rhythmicity, which causes age-associated physiological alterations. However, interactions between the circadian clock and aging have been rarely studied in plants. Here, we investigated potential roles for the circadian clock in the regulation of leaf senescence in plants. Members of the evening complex in <I>Arabidopsis</I> circadian clock, EARLY FLOWERING 3 (ELF3), EARLY FLOWERING 4 (ELF4), and LUX ARRHYTHMO (LUX), as well as the morning component PSEUDO-RESPONSE REGULATOR 9 (PRR9), affect both age-dependent and dark-induced leaf senescence. The circadian clock regulates the expression of several senescence-related transcription factors. In particular, PRR9 binds directly to the promoter of the positive aging regulator <I>ORESARA1</I> (<I>ORE1</I>) gene to promote its expression. PRR9 also represses <I>miR164</I>, a posttranscriptional repressor of <I>ORE1</I>. Consistently, genetic analysis revealed that delayed leaf senescence of a <I>prr9</I> mutant was rescued by <I>ORE1</I> overexpression. Thus, PRR9, a core circadian component, is a key regulator of leaf senescence via positive regulation of <I>ORE1</I> through a feed-forward pathway involving posttranscriptional regulation by <I>miR164</I> and direct transcriptional regulation. Our results indicate that, in plants, the circadian clock and leaf senescence are intimately interwoven as are the clock and aging in animals.</P></▼2>