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1
Nouri, N. M., S. M. H. Mirsaeedi, and M. Moghimi. "Large eddy simulation of natural cavitating flows in Venturi-type sections." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 225, no. 2 (June 23, 2010): 369–81. http://dx.doi.org/10.1243/09544062jmes2036.
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Large eddy simulation (LES) is used here to model the cavitating flow at a Venturi-type section. Cavitating flows can occur in a wide range of applications. The flow is represented here by means of LES, which compared to Reynolds-averaged Navier—Stokes (RANS) has the advantage that in it the large, energy-containing structures are resolved directly, whereas most of these structures are modelled in RANS. This gives LES an improved fidelity over RANS, although, due to the time averaging, the required computational time is considerably lower for RANS than for LES. The conclusion of this work shows that the qualitative comparisons with earlier preliminary data and the simulated general cavitation behaviour correlate reasonably well with experimental observations and that the simulations have the ability to predict cavitation cycle in more detail.
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Mejia, Omar, Jhon Quiñones, and Santiago Laín. "RANS and Hybrid RANS-LES Simulations of an H-Type Darrieus Vertical Axis Water Turbine." Energies 11, no. 9 (September 6, 2018): 2348. http://dx.doi.org/10.3390/en11092348.
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Nowadays, the global energy crisis has encouraged the use of alternative sources like the energy available in the water currents of seas and rivers. The vertical axis water turbine (VAWT) is an interesting option to harness this energy due to its advantages of facile installation, maintenance and operation. However, it is known that its efficiency is lower than that of other types of turbines due to the unsteady effects present in its flow physics. This work aims to analyse through Computational Fluid Dynamics (CFD) the turbulent flow dynamics around a small scale VAWT confined in a hydrodynamic tunnel. The simulations were developed using the Unsteady Reynolds Averaged Navier Stokes (URANS), Detached Eddy Simulation (DES) and Delayed Detached Eddy Simulation (DDES) turbulence models, all of them based on k-ω Shear Stress Transport (SST). The results and analysis of the simulations are presented, illustrating the influence of the tip speed ratio. The numerical results of the URANS model show a similar behaviour with respect to the experimental power curve of the turbine using a lower number of elements than those used in the DES and DDES models. Finally, with the help of both the Q-criterion and field contours it is observed that the refinements made in the mesh adaptation process for the DES and DDES models improve the identification of the scales of the vorticity structures and the flow phenomena present on the near and far wake of the turbine.
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Kissner, Carolin, Sébastien Guérin, Pascal Seeler, Mattias Billson, Paruchuri Chaitanya, Pedro Carrasco Laraña, Hélène de Laborderie, et al. "ACAT1 Benchmark of RANS-Informed Analytical Methods for Fan Broadband Noise Prediction—Part I—Influence of the RANS Simulation." Acoustics 2, no. 3 (July 22, 2020): 539–78. http://dx.doi.org/10.3390/acoustics2030029.
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A benchmark of Reynolds-Averaged Navier-Stokes (RANS)-informed analytical methods, which are attractive for predicting fan broadband noise, was conducted within the framework of the European project TurboNoiseBB. This paper discusses the first part of the benchmark, which investigates the influence of the RANS inputs. Its companion paper focuses on the influence of the applied acoustic models on predicted fan broadband noise levels. While similar benchmarking activities were conducted in the past, this benchmark is unique due to its large and diverse data set involving members from more than ten institutions. In this work, the authors analyze RANS solutions performed at approach conditions for the ACAT1 fan. The RANS solutions were obtained using different CFD codes, mesh resolutions, and computational settings. The flow, turbulence, and resulting fan broadband noise predictions are analyzed to pinpoint critical influencing parameters related to the RANS inputs. Experimental data are used for comparison. It is shown that when turbomachinery experts perform RANS simulations using the same geometry and the same operating conditions, the most crucial choices in terms of predicted fan broadband noise are the type of turbulence model and applied turbulence model extensions. Chosen mesh resolutions, CFD solvers, and other computational settings are less critical.
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Secundov, Alexander N., Stanley F. Birch, and Paul G. Tucker. "Propulsive jets and their acoustics." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 365, no. 1859 (May 22, 2007): 2443–67. http://dx.doi.org/10.1098/rsta.2007.2017.
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The complex flow physics challenges and asks questions regarding these challenges a wide range of jet flows found in aerospace engineering. Hence, the daunting task facing Reynolds-averaged Navier–Stokes (RANS) technology, for which the time average of the turbulent flow field is solved, is set out. Despite the clear potential of large eddy simulation (LES)-related methods and hybrid forms involving some RANS modelling, numerous current deficiencies, mostly related to the limitations of computational resources, are identified. It is concluded that currently, these limitations make LES and hybrids most useful for understanding flow physics and refining RANS technology. The use of LES in conjunction with a ray-tracing model to elucidate the physics of acoustic wave transmission in jets and thus improved RANS technology is described. It is argued that, as a stopgap measure, pure RANS simulations can be a valuable part of the design process and can now predict acoustics spectra and directivity diagrams with useful accuracy. Ultimately, hybrid RANS–LES-type methods, and then pure LES, will dominate, but the time-scales for this transition suggests that improvements to RANS technology should not be ignored.
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Ma, Baolong, Yujiro Ikeda, Yoshie Otake, Makoto Teshigawara, Yasuo Wakabayashi, Masahide Harada, Motoki Ooi, Takao Hashiguchi, Yutaka Yamagata, and Shin Takeda. "Slab geometry type cold neutron moderator development based on neutronic study for Riken Accelerator-driven compact Neutron Source (RANS)." EPJ Web of Conferences 231 (2020): 04004. http://dx.doi.org/10.1051/epjconf/202023104004.
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Cold neutrons with energy less than several meV are good probes for material research, and they have been available on large neutron facilities, whereas it is not commonly available on compact accelerator-driven neutron source. RIKEN Accelerator-driven Neutron Source (RANS) is a pulsed neutron facility which provides thermal neutrons and high energy neutrons at several MeV. We started a project to implement a cold neutron moderator for RANS to broaden cold neutrons applications. A cold neutron moderator system with a mesitylene moderator at 20K and a polyethylene pre-moderator at room temperature in the slab geometry was designed for RANS. So far, the thickness of the pre-moderator and mesitylene have been optimized to get the highest cold neutron flux by using a Monte Carlo simulation code, PHITS. Graphite reflector dimensions were also proven to have significant effect to increase the cold neutron intensity.
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Mahak, M., IZ Naqavi, and PG Tucker. "Cost-effective hybrid RANS-LES type method for jet turbulence and noise prediction." International Journal of Aeroacoustics 16, no. 1-2 (February 20, 2017): 97–111. http://dx.doi.org/10.1177/1475472x16684702.
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Jets at higher Reynolds numbers have a high concentration of energy in small scales in the nozzle vicinity. This is challenging for large-eddy simulation, potentially placing severe demands on grid density. To circumvent this, we propose a novel procedure based on well-known Reynolds number (Re) independent of jets. We reduce the jet Re while rescaling the boundary layer properties to maintain incoming boundary layer thickness consistent with high Re jet. The simulations are carried out using hybrid large-eddy simulation type of approach which is incorporated by using near-wall turbulence model with modified properties. No subgrid scale model is used in these simulations. Hence, they effectively become numerical large-eddy simulation with Reynolds-averaged Navier–Stokes covering the full boundary layer region. The noise post-processing is carried out using the Ffowcs-Williams-Hawking approach. The simulations are made for Mach numbers (M) of 0.75 and 0.875 (cold and hot). The results for the overall sound pressure level are observed to be within 2–3% of the measurements, and directivity of sound is also captured accurately for both the cases. Hence, the low Re simulations can be more beneficial in saving time and cost while providing reasonably accurate results.
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Lardeau, Sylvain, Ning Li, and Michael A. Leschziner. "Large Eddy Simulation of Transitional Boundary Layers at High Free-Stream Turbulence Intensity and Implications for RANS Modeling." Journal of Turbomachinery 129, no. 2 (July 14, 2006): 311–17. http://dx.doi.org/10.1115/1.2436896.
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Large-eddy simulations of transitional flows over a flat plate have been performed for different sets of free-stream-turbulence conditions. Interest focuses, in particular, on the unsteady processes in the boundary layer before transition occurs and as it evolves, the practical context being the flow over low-pressure turbine blades. These considerations are motivated by the wish to study the realism of a RANS-type model designed to return the laminar fluctuation energy observed well upstream of the location at which transition sets in. The assumptions underlying the model are discussed in the light of turbulence-energy budgets deduced from the simulations. It is shown that the pretransitional field is characterized by elongated streaky structures which, notwithstanding their very different structural properties relative to fully established turbulence, lead to the amplification of fluctuations by conventional shear-stress/shear-strain interaction, rather than by pressure diffusion, the latter being the process underpinning the RANS-type transitional model being investigated.
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Secretan, Y., M. Leclerc, S. Duchesne, and M. Heniche. "Une méthodologie de modélisation numérique de terrain pour la simulation hydrodynamique bidimensionnelle." Revue des sciences de l'eau 14, no. 2 (April 12, 2005): 187–212. http://dx.doi.org/10.7202/705417ar.
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L'article pose la problématique de la construction du Modèle Numérique de Terrain (MNT) dans le contexte d'études hydrauliques à deux dimensions, ici reliées aux inondations. La difficulté est liée à l'hétérogénéité des ensembles de données qui diffèrent en précision, en couverture spatiale, en répartition et en densité, ainsi qu'en géoréférentiation, notamment. Dans le cadre d'un exercice de modélisation hydrodynamique, toute la région à l'étude doit être documentée et l'information portée sur un support homogène. L'article propose une stratégie efficace supportée par un outil informatique, le MODELEUR, qui permet de fusionner rapidement les divers ensembles disponibles pour chaque variable qu'elle soit scalaire comme la topographie ou vectorielle comme le vent, d'en préserver l'intégrité et d'y donner accès efficacement à toutes les étapes du processus d'analyse et de modélisation. Ainsi, quelle que soit l'utilisation environnementale du modèle numérique de terrain (planification d'aménagement, conservation d'habitats, inondations, sédimentologie), la méthode permet de travailler avec la projection des données sur un support homogène de type maillage d'éléments finis et de conserver intégralement l'original comme référence. Cette méthode est basée sur une partition du domaine d'analyse par type d'information : topographie, substrat, rugosité de surface, etc.. Une partition est composée de sous-domaines et chacun associe un jeu de données à une portion du domaine d'analyse par un procédé déclaratoire. Ce modèle conceptuel forme à notre sens le MNT proprement dit. Le processus de transfert des données des partitions à un maillage d'analyse est considéré comme un résultat du MNT et non le MNT lui-même. Il est réalisé à l'aide d'une technique d'interpolation comme la méthode des éléments finis. Suite aux crues du Saguenay en 1996, la méthode a pu être testée et validée pour en démontrer l'efficacité. Cet exemple nous sert d'illustration.
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Mnasri, Aida, and Ezzeddine Hadj Taieb. "Simulation numérique par éléments finis des écoulements transitoires à surface libre." La Houille Blanche, no. 5-6 (December 2019): 81–92. http://dx.doi.org/10.1051/lhb/2019032.
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Une simulation numérique par des éléments finis des écoulements transitoires à surface libre dans les canaux prismatiques est présentée. Dans cette étude, l'écoulement est supposé unidirectionnel dans un canal de faible pente. Le modèle mathématique est constitué d'un système de deux équations aux dérivées partielles de type hyperbolique résolu numériquement par la méthode des éléments finis. Pour définir les fonctions d'interpolation dans la forme intégrale des résidus pondérés, la méthode de Galerkin a été utilisée. Dans les applications, différentes sections prismatiques sont examinées. Les régimes transitoires étudiés sont dus à des manœuvres de vanne placée en aval du canal, l'extrémité amont étant connectée à un réservoir de niveau constant. Dans ces conditions, le régime transitoire correspond à une évolution de l'écoulement d'un régime permanent initial vers un régime permanent final. Ces deux régimes sont supposés uniformes à débit constant défini par la formule de Manning. Les résultats obtenus concernent l'évolution des paramètres hydrauliques en différentes sections du canal, suite à la manœuvre en aval. Deux cas de manœuvres sont considérés ; le cas d'une ouverture et le cas d'une fermeture. L'étude a permis d'analyser la propagation des ondes de surface et la réflexion de ces ondes sur les deux extrémités du canal. En particulier, les résultats numériques montrent que lorsque la largeur du lit du canal est très petite (cas de la section triangulaire), les fluctuations des profondeurs sont rapidement amorties.
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Davidson, Josh, and Ronan Costello. "Efficient Nonlinear Hydrodynamic Models for Wave Energy Converter Design—A Scoping Study." Journal of Marine Science and Engineering 8, no. 1 (January 11, 2020): 35. http://dx.doi.org/10.3390/jmse8010035.
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This review focuses on the most suitable form of hydrodynamic modeling for the next generation wave energy converter (WEC) design tools. To design and optimize a WEC, it is estimated that several million hours of operation must be simulated, perhaps one million hours of WEC simulation per year of the R&D program. This level of coverage is possible with linear potential flow (LPF) models, but the fidelity of the physics included is not adequate. Conversely, while Reynolds averaged Navier–Stokes (RANS) type computational fluid dynamics (CFD) solvers provide a high fidelity representation of the physics, the increased computational burden of these models renders the required amount of simulations infeasible. To scope the fast, high fidelity options, the present literature review aims to focus on what CFD theories exist intermediate to LPF and RANS as well as other modeling options that are computationally fast while retaining higher fidelity than LPF.
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Chillon, Sergio, Antxon Uriarte-Uriarte, Iñigo Aramendia, Pablo Martínez-Filgueira, Unai Fernandez-Gamiz, and Iosu Ibarra-Udaeta. "jBAY Modeling of Vane-Type Vortex Generators and Study on Airfoil Aerodynamic Performance." Energies 13, no. 10 (May 12, 2020): 2423. http://dx.doi.org/10.3390/en13102423.
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The increased demand for wind power is related to changes in the sizes of wind turbines and the development of flow control devices, such as vortex generators (VGs). In the present study, an analysis of the vortices generated by a vane-type VG is performed. To that end, the aerodynamic performance of a DU97W300 airfoil with and without VG is evaluated. The jBAY source term model was implemented for simulation of a triangular-shaped VG and the resolution of the fully meshed computational fluid dynamics (CFD) model. Reynolds-averaged Navier–Stokes (RANS) based simulations were used to calculate the effect of VGs in steady state, and the detached eddy simulation (DES) method was used for angles of attack (AoAs) around the stall situation. All jBAY based numerical simulations were carried out with a Reynolds number of Re = 2 × 106 to analyze the influence of VGs with AoAs between 0 and 20° and were validated versus experimental wind tunnel results. The results show that setting up a VG device on an airfoil benefits its aerodynamic performance and that the use of the jBAY model for simulation is accurate and efficient.
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Ibarra-Udaeta, Iosu, Koldo Portal-Porras, Alejandro Ballesteros-Coll, Unai Fernandez-Gamiz, and Javier Sancho. "Accuracy of the Cell-Set Model on a Single Vane-Type Vortex Generator in Negligible Streamwise Pressure Gradient Flow with RANS and LES." Journal of Marine Science and Engineering 8, no. 12 (December 2, 2020): 982. http://dx.doi.org/10.3390/jmse8120982.
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Passive flow control devices are included in the design of wind turbine blades in order to obtain better performance and reduce loads without consuming any external energy. Vortex Generators are one of the most popular flow control devices, whose main objective is to delay the flow separation and increase the maximum lift coefficient. Computational Fluid Dynamics (CFD) simulations of a Vortex Generator (VG) on a flat plate in negligible streamwise pressure gradient conditions with the fully-resolved mesh model and the cell-set model using Large Eddy Simulation (LES) and Reynolds-Averaged Navier-Stokes (RANS) were carried out, with the objective of evaluating the accuracy of the cell-set model taking the fully-resolved mesh model as benchmark. The implementation of the cell-set model entailed a considerable reduction of the number of cells, which entailed saving simulation time and resources. The coherent structures, vortex path, wall shear stress and size, strength and velocity profiles of the primary vortex have been analyzed. The results show good agreements between the fully-resolved mesh model and the cell-set mode with RANS in all the analyzed parameters. With LES, acceptable results were obtained in terms of coherent structures, vortex path and wall shear stress, but slight differences between models are visible in the size, strength and velocity profiles of the primary vortex. As this is considered the first application of the cell-set model on VGs, further research is proposed, since the implementation of the cell-set model can represent an advantage over the fully-resolved mesh model.
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Castelli, Marco Raciti, and Ernesto Benini. "Numerical Simulation of a Straight-Bladed Vertical-Axis Water Turbine Operating in a 2 m/s Current." Applied Mechanics and Materials 325-326 (June 2013): 162–66. http://dx.doi.org/10.4028/www.scientific.net/amm.325-326.162.
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The present work proposes a full campaign of simulation of a Darrieus-type Vertical-Axis Water Turbine (VAWaterT) operating in an open flow-field. After describing the computational model and the relative validation procedure, a complete campaign of simulations based on full RANS unsteady calculations is presented for a three-bladed rotor architecture, characterized by a NACA 0025 blade profile. Flow field characteristics are investigated for several values of tip speed ratio and for a constant unperturbed free-stream water velocity of 2 m/s. Finally, the torque coefficient generated from the three blades is determined for each simulated angular velocity, allowing the calculation of the rotor power-curve. Keywords: Vertical-Axis Water Turbine, hydrokinetic technology, CFD, NACA 0025.
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Shen, Cheng Jun, Cui Lan Gao, and Ya Min Song. "Numerical Simulation of Wind Environment in a Hill and Buildings Configuration." Applied Mechanics and Materials 641-642 (September 2014): 544–49. http://dx.doi.org/10.4028/www.scientific.net/amm.641-642.544.
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Numerical simulation of air flow over urban areas is an effective way to analyze and predict the wind environment. This paper presents two dimensional computer model results concerning the effects of buildings and/or a hill on the wind flow. The RANS equations and RNG κ-ε turbulence model used in the simulation are discretized by the finite volume method. The computational solution is based on a pressure correction algorithm of the SIMPLE-type. The inflow boundary conditions are given by wind tunnel experiment. In the presence of only a street canyon formed by two buildings, the ambient wind is accelerated and slightly curved at the roof level. When there exist a hill and a street canyon, the velocity in the canyon is affected by the upwind hill. Another simulation model, which has a hill and two street canyons, is used for comparison. There is a little difference in velocity between a single street canyon and two canyons in the presence of an upwind hill.
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Xie, Yi, and Xiang Dong Xia. "CFD Simulation for Displacement Deep-Vee Vessels on Resistance Influence Factor." Applied Mechanics and Materials 55-57 (May 2011): 692–97. http://dx.doi.org/10.4028/www.scientific.net/amm.55-57.692.
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Resistance influence factors of displacement type Deep-vee forms are analyzed with eight hull forms provided. The free surface viscous flow of these forms is calculated by air-water two phases RANS equations with RNG turbulence model and volume of fraction method. Total resistance, pressure distribution and wave profile of bow are presented. Some results can be taken as follows: while maintaining the same tonnage, L/B ratio and draft, the resistance performance of Deep-Vee vessels is excellent at high speed if a large transverse dead rise angle was located from 50%front midship to 25% backward midship; The resistance performance at a lesser L/B and draft is worse if the displacement and dead rise angle is the same; Furthermore, it can be improved by a cigar-shaped bulbous bow. The change of pressure distribution for cigar-shaped bulbous bow is more slightly than that of tobacco pipe-shaped bulbous bow.
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Arunkumar, H. S., Chidanand Mangrulkar, and Trushar Gohil. "Vortex dynamics and elliptical structure wake interaction in the proximity of wall using 2-D RANS simulation." MATEC Web of Conferences 144 (2018): 04018. http://dx.doi.org/10.1051/matecconf/201814404018.
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The 2-D numerical study is performed to analyses the flow characteristic behind the elliptical structure placed near the wall for three different gap ratios as 0.25, 0.5, and 1.0. Computational domain and model is initially validated with the unbounded flow over a cylinder without considering wall effect for Reynolds number of 3900. For flow over the cylinder with near wall, computational domain is modelled as Blasius profile is the input to the area of interest. At different gap ratios the effect of boundary layer on vortex shedding is studied with Reynolds number of 1440. By applying different turbulent model for analysis, study the variation in the results and suggest the suitable model for the present type of study. It has been observed that the wall effect is predominant in case of the gap ratio of 0.25 as compared to other gap ratios.
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Su, Xiangyu, Xiaodong Ren, Xuesong Li, and Chunwei Gu. "Unsteadiness of Tip Leakage Flow in the Detached-Eddy Simulation on a Transonic Rotor with Vortex Breakdown Phenomenon." Energies 12, no. 5 (March 12, 2019): 954. http://dx.doi.org/10.3390/en12050954.
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Tip leakage vortex (TLV) in a transonic compressor rotor was investigated numerically using detached-eddy simulation (DES) method at different working conditions. Strong unsteadiness was found at the tip region, causing a considerable fluctuation in total pressure distribution and flow angle distribution above 80% span. The unsteadiness at near choke point and peak efficiency point is not obvious. DES method can resolve more detailed flow patterns than RANS (Reynolds-averaged Navier–Stokes) results, and detailed structures of the tip leakage flow were captured. A spiral-type breakdown structure of the TLV was successfully observed at the near stall point when the TLV passed through the bow shock. The breakdown of TLV contributed to the unsteadiness and the blockage effect at the tip region.
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Feng, Feng, Xin Chang, Xiang Ru Cheng, and Xiang Yang Qi. "Research on Hydrodynamic Performance of Front-Mounted Water Separation Propeller." Applied Mechanics and Materials 166-169 (May 2012): 2976–81. http://dx.doi.org/10.4028/www.scientific.net/amm.166-169.2976.
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The Front-mounted Water Separation Propeller is a new-type energy saving propulsion device, on which it’s necessary to make research. A numerical simulation on the hydrodynamic performance of the Front-mounted Water Separation Propeller by RANS method was performed. The simple ship models with and without Front-mounted Water Separation Propeller were established and meshed by using hybrid grid. The drag performances of the ship model with and without Front-mounted Water Separation Propeller were performed separately by using Kω-SST turbulence model and VOF model. The method provided in this article is proved to be effective by make comparison between the simulation results and the model test results. The results show that the ship resistance can be reduced by using the Front-mounted Water Separation Propeller.
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SWAMINATHAN, N., G. XU, A. P. DOWLING, and R. BALACHANDRAN. "Heat release rate correlation and combustion noise in premixed flames." Journal of Fluid Mechanics 681 (June 29, 2011): 80–115. http://dx.doi.org/10.1017/jfm.2011.232.
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The sound emission from open turbulent flames is dictated by the two-point spatial correlation of the rate of change of the fluctuating heat release rate. This correlation in premixed flames can be represented well using Gaussian-type functions and unstrained laminar flame thermal thickness can be used to scale the correlation length scale, which is about a quarter of the planar laminar flame thermal thickness. This correlation and its length scale are observed to be less influenced by the fuel type or stoichiometry or turbulence Reynolds and Damkohler numbers. The time scale for fluctuating heat release rate is deduced to be about τc/34 on an average, where τc is the planar laminar flame time scale, using direct numerical simulation (DNS) data. These results and the spatial distribution of mean reaction rate obtained from Reynolds-averaged Navier–Stokes (RANS) calculations of open turbulent premixed flames employing the standard model and an algebraic reaction rate closure, involving a recently developed scalar dissipation rate model, are used to obtain the far-field sound pressure level from open flames. The calculated values agree well with measured values for flames of different stoichiometry and fuel types, having a range of turbulence intensities and heat output. Detailed analyses of RANS results clearly suggest that the noise level from turbulent premixed flames having an extensive and uniform spatial distribution of heat release rate is low.
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Mortel, Christian M., Nicanor L. Serrano, and John Gabriel G. Decena. "Optimization of Straight-bladed Darrieus type vertical axis wind blade for low wind speed." E3S Web of Conferences 211 (2020): 02008. http://dx.doi.org/10.1051/e3sconf/202021102008.
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Straight-bladed Darrieus blade is a type of vertical axis wind turbine that requires low wind speed to operate but is considered less efficient due to conventional blade geometry. To increase its performance by means of dynamic torque, the study used a statistical method, central composite design, through DesignExpert software. The computational fluid dynamics (CFD) through SolidWorks Reynolds-Averaged Navier Stokes Equation (RANS) k – epsilon turbulence model was used to simulate the Design of Experiments. The study was composed of two phases, namely 2D and 3D simulations. The 2D simulation studied the effect of varying the camber, camber location, and thickness to the dynamic torque, while the 3D simulation varied the blade height, rotor radius, and materials. The camber’s optimal conditions, camber location, and thickness in 2D simulations are 4.75%, 45%, and 15.50% of the chord, respectively. These optimal design values could reach the dynamic torque equivalent to 60.6571 Newton-meter. Meanwhile, the blade height and rotor radius of the 3D simulations have optimal design values of 4.41 meters and 4.75 meters, respectively. These optimal values could increase the dynamic torque to 2310.01 Newton-meter. The dynamic torque of the optimal design obtained a 133% significant increase compared to the conventional blade. Thus, the research has proven the increase in the Darrieus Wind turbine’s performance by varying its blade geometry.
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Orihara, Hideo, and Hideaki Miyata. "Numerical Simulation Method for Flows About a Semi-Planing Boat with a Transom Stern." Journal of Ship Research 44, no. 03 (September 1, 2000): 170–85. http://dx.doi.org/10.5957/jsr.2000.44.3.170.
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A new simulation method based on computational fluid dynamics (CFD) is developed for a semiplaning boat with a transom stern in unsteady motion. The time-dependent Reynolds-averaged Navier-Stokes (RANS) equation is discretized by the finite-volume method and solved by the MAC-type solution algorithm, The free-surface treatment in this study is based on the density function method. The motion of the boat is simultaneously solved by combining the equation of the motion of the boat with the flow computation, and the effect of the boat motion is implemented by the moving grid method in the flow computation. Simulations for two types of practical high-speed boats are performed in the Froude number range from 0.5 to 1.0 and the results are compared with experimental ones. It is demonstrated that this method can simulate both the flow about the boat and the running attitude in free-to-run condition with a sufficient degree of accuracy and that it can be used as an effective tool for the development of hull form of practical high-speed boats.
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Faingold, Galia, Leonid Tartakovsky, and Steven Frankel. "Numerical Study of a Direct Injection Internal Combustion Engine Burning a Blend of Hydrogen and Dimethyl Ether." Drones 2, no. 3 (July 24, 2018): 23. http://dx.doi.org/10.3390/drones2030023.
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In the reported study, various aspects of dimethyl ether/hydrogen combustion in a Reactivity Controlled Compression Ignition (RCCI) engine are numerically evaluated using Reynolds Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES). Early direct injection and mixture propagation were also explored, along with peculiaritis of dimethyl ether combustion modeling. The numerical models are validated using available experimental results of a partially premixed dimethyl ether jet flames and an optically accessible internal combustion engine with direct hydrogen injection. LES showed more predictive results in modeling both combustion and mixture propagation. The same models were applied to a full engine cycle of an RCCI engine with stratified reactivity, to gain phenomenological insight into the physical processes involved in stratified reactivity combustion. We showed that 3D and turbulence considerations had a great impact on simulation results, and the LES was able to capture the pressure oscillations typical for this type of combustion.
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Yan, Mingfei, Yasuo Wakabayashi, Yoshie Otake, Yujiro Ikeda, Atsushi Taketani, Takao Hashiguchi, Sheng Wang, et al. "Reconstruction on fast neutron CT for concrete structure inspection with a pixel-type detector by applying linear scanning method." EPJ Web of Conferences 231 (2020): 05008. http://dx.doi.org/10.1051/epjconf/202023105008.
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Concrete structure has been widely used in bridges and highways, however, its performance will be deteriorated after long term serving or suffering disaster. Since fast neutron has strong transmission ability and is sensitive to water content in the concrete structure, it can provide an effective probe to inspect the inner structure of concrete with non-destructive way. Thus, we propose a fast neutron imaging and reconstruction system of 3D CT for concrete structure inspection with Riken accelerator-driven compact neutron source (RANS) using a fast neutron pixel-type detector, which has 8×8 pixels. To have a good space resolution on the reconstructed image, a rotation + linear scanning method is devised and is used to collect the projection data from experiment or calculation. In this paper, reconstruction for a concrete object containing both iron bars and acrylic bars for simulation of water has been conducted. As a result, 3D image of 1cm diameter bar is reconstructed by the sparse reconstruction algorithm.
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Wang, Wei, Dagang Zhao, Chunyu Guo, and Yongjie Pang. "Analysis of Hydrodynamic Performance of L-Type Podded Propulsion with Oblique Flow Angle." Journal of Marine Science and Engineering 7, no. 2 (February 20, 2019): 51. http://dx.doi.org/10.3390/jmse7020051.
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In this study, the Reynolds-averaged Navier–Stokes (RANS) method and a model experimental test in a towing tank are used to investigate the unsteady hydrodynamic performance of L-type podded propulsion under different oblique flow angles and advance coefficients. The results show that the load of the operative propeller increases with oblique flow angle and the bracket adds resistance to the pod due to the impact of water flow, leading to a reduced propeller thrust coefficient with increased oblique flow angle. Under a high advance coefficient, the speed of increase of the pressure effect is higher than that of the viscosity effect, and the propeller efficiency increases with the oblique flow angle. The nonuniformity of the inflow results in varying degrees of asymmetry in the horizontal and vertical distributions of the propeller blade pressure. Under high oblique flow angle, relatively strong interference effects are seen between venting vortexes and the cabin after blades, leading to a disorderly venting vortex system after the blade. The numerical simulation results are in good agreement with the experimental values. The study findings provide a foundation for further research on L-type podded propulsors.
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Gómez, Manuel, Joan Recasens, Beniamino Russo, and Eduardo Martínez-Gomariz. "Assessment of inlet efficiency through a 3D simulation: numerical and experimental comparison." Water Science and Technology 74, no. 8 (August 9, 2016): 1926–35. http://dx.doi.org/10.2166/wst.2016.326.
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Inlet efficiency is a requirement for characterizing the flow transfers between surface and sewer flow during rain events. The dual drainage approach is based on the joint analysis of both upper and lower drainage levels, and the flow transfer is one of the relevant elements to define properly this joint behaviour. This paper presents the results of an experimental and numerical investigation about the inlet efficiency definition. A full scale (1:1) test platform located in the Technical University of Catalonia (UPC) reproduces both the runoff process in streets and the water entering the inlet. Data from tests performed on this platform allow the inlet efficiency to be estimated as a function of significant hydraulic and geometrical parameters. A reproduction of these tests through a numerical three-dimensional code (Flow-3D) has been carried out simulating this type of flow by solving the RANS equations. The aim of the work was to reproduce the hydraulic performance of a previously tested grated inlet under several flow and geometric conditions using Flow-3D as a virtual laboratory. This will allow inlet efficiencies to be obtained without previous experimental tests. Moreover, the 3D model allows a better understanding of the hydraulics of the flow interception and the flow patterns approaching the inlet.
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Kocaman, Selahattin, Hasan Güzel, Stefania Evangelista, Hatice Ozmen-Cagatay, and Giacomo Viccione. "Experimental and Numerical Analysis of a Dam-Break Flow through Different Contraction Geometries of the Channel." Water 12, no. 4 (April 15, 2020): 1124. http://dx.doi.org/10.3390/w12041124.
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Dam-break wave propagation usually occurs over irregular topography, due for example to natural contraction-expansion of the river bed and to the presence of natural or artificial obstacles. Due to limited available dam-break real-case data, laboratory and numerical modeling studies are significant for understanding this type of complex flow problems. To contribute to the related field, a dam-break flow over a channel with a contracting reach was investigated experimentally and numerically. Laboratory tests were carried out in a smooth rectangular channel with a horizontal dry bed for three different lateral contraction geometries. A non-intrusive digital imaging technique was utilized to analyze the dam-break wave propagation. Free surface profiles and time variation of water levels in selected sections were obtained directly from three synchronized CCD video camera records through a virtual wave probe. The experimental results were compared against the numerical solution of VOF (Volume of Fluid)-based Shallow Water Equations (SWEs) and Reynolds-Averaged Navier-Stokes (RANS) equations with the k-ε turbulence model. Good agreements were obtained between computed and measured results. However, the RANS solution shows a better correspondence with the experimental results compared with the SWEs one. The presented new experimental data can be used to validate numerical models for the simulation of dam-break flows over irregular topography.
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Li, Liang, Guo-Yan Zhao, Hong-Bo Wang, Ming-Bo Sun, Da-Peng Xiong, Tao Tang, and Ming-Jiang Liu. "A general framework of high-resolution hybrid central/WENO numerical scheme for turbulent compressible simulation." Modern Physics Letters B 35, no. 07 (February 18, 2021): 2150118. http://dx.doi.org/10.1142/s0217984921501189.
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This work presents a general framework of finite-difference hybrid scheme which contains a linear central scheme and a nonl-inear WENO scheme. A new optimal-designed shock sensor is used to distinguish the smoothness of flowfield and a binary-type weighting function is used to switch sub-schemes rationally. Based on the above improvements, the effects of different combinations of each component within the hybrid scheme are characterized in linear advection equation and Euler equations. The maximum reference threshold values are provided. Extensive test cases indicate the hybrid scheme’s numerical robustness, low-dissipation, and superior computational efficiency. Specifically, benefited from the high-resolution shock sensor which can accurately perceive shocks without excessive misidentifications, the hybrid scheme can achieve non-oscillatory solutions, and resolve more vortices in smooth regions compared to the original shock-capturing scheme. Meanwhile, the superiority of the hybrid scheme is further confirmed in the Reynolds-averaged Navier–Stokes equations/Lager Eddy Simulations (RANS/LES) for the DLR scramjet combustor case with viscous terms and/or sub-grid scale models are used. The present hybrid framework can be easily implemented within the existing numerical simulation code framework.
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Hien, Le Thi Thu, and Duong Hoai Duc. "Numerical Simulation of Free Surface Flow on Spillways and Channel Chutes with Wall and Step Abutments by Coupling Turbulence and Air Entrainment Models." Water 12, no. 11 (October 29, 2020): 3036. http://dx.doi.org/10.3390/w12113036.
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Spillways and channel chutes are widely used in hydraulic works. Two kinds of abutment—walls and steps—are usually constructed to dissipate energy; however, they may also cause cavitation at the abutment position. In this study, we used Flow 3D with the Reynolds-averaged Navier–Stokes (RANS) and large eddy simulation (LES) turbulent models which included air entrainment to simulate the free surface flow through the spillway, channel chute and stilling basin of the Ngan Truoi construction to optimize the configuration of walls and dams. We measured the water level, velocity and pressure to estimate the influence of grid size and the turbulent model type used. Our results highlight the need to include air entrainment in the model simulating rapid flow over a hydraulic construction. With adjustments for energy loss, this study shows that walls provide the best results and the optimal distance between two walls is 2.8 m.
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Nazififard, Mohammad. "Computational fluid dynamic simulation of swirl flow in hexagonal rod bundle geometry by split mixing vane grid spacers." Thermal Science 23, no. 5 Part B (2019): 3143–52. http://dx.doi.org/10.2298/tsci171006076n.
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Heat transfer and pressure drop are numerically investigated for turbulent flows through a hexagonal fuel rod bundle. For the purpose of numerical analysis, the geometric and boundary conditions were taken from the VVER-1000. Since VVER-1000 does not have mixing vane on the grid spacer of the fuel assembly, split mixing vane is designed to boost turbulent flow and heat transfer in the rod bundle subchannels. The computational domain including two grid spacers extend from 100 ? Dh upstream of the first grid spacer to 250 ? Dh downstream of the second grid spacer. The steady-state form of the RANS, mass, energy and turbulence equations was discretized and solved using ANSYS-CFX. The standard k-? model is employed to simulate turbulence. The results show a considerable increase in the average heat transfer to ~10 ? Dh downstream of the grid spacer using the mixing vane on the grid spacer of VVER type reactor. As expected, the pressure loss through the grid spacer also increased slightly with the mixing vanes.
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Contreras, Leidy, Omar Lopez, and Santiago Lain. "Computational Fluid Dynamics Modelling and Simulation of an Inclined Horizontal Axis Hydrokinetic Turbine." Energies 11, no. 11 (November 14, 2018): 3151. http://dx.doi.org/10.3390/en11113151.
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In this contribution, unsteady three-dimensional numerical simulations of the water flow through a horizontal axis hydrokinetic turbine (HAHT) of the Garman type are performed. This study was conducted in order to estimate the influence of turbine inclination with respect to the incoming flow on turbine performance and forces acting on the rotor, which is studied using a time-accurate Reynolds-averaged Navier-Stokes (RANS) commercial solver. Changes of the flow in time are described by a physical transient model based on two domains, one rotating and the other stationary, combined with a sliding mesh technique. Flow turbulence is described by the well-established Shear Stress Transport (SST) model using its standard and transitional versions. Three inclined operation conditions have been analyzed for the turbine regarding the main stream: 0° (SP configuration, shaft parallel to incoming velocity), 15° (SI15 configuration), and 30° (SI30 configuration). It was found that the hydrodynamic efficiency of the turbine decreases with increasing inclination angles. Besides, it was obtained that in the inclined configurations, the thrust and drag forces acting on rotor were lower than in the SP configuration, although in the former cases, blades experience alternating loads that may induce failure due to fatigue in the long term. Moreover, if the boundary layer transitional effects are included in the computations, a slight increase in the power coefficient is computed for all inclination configurations.
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Granados-Ortiz, Francisco-Javier, Joaquin Ortega-Casanova, and Choi-Hong Lai. "Two-step numerical simulation of the heat transfer from a flat plate to a swirling jet flow from a rotating pipe." International Journal of Numerical Methods for Heat & Fluid Flow 30, no. 1 (November 18, 2019): 143–75. http://dx.doi.org/10.1108/hff-04-2019-0343.
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Purpose Impinging jets have been widely studied, and the addition of swirl has been found to be beneficial to heat transfer. As there is no literature on Reynolds-averaged Navier Stokes equations (RANS) nor experimental data of swirling jet flows generated by a rotating pipe, the purpose of this study is to fill such gap by providing results on the performance of this type of design. Design/methodology/approach As the flow has a different behaviour at different parts of the design, the same turbulent model cannot be used for the full domain. To overcome this complexity, the simulation is split into two coupled stages. This is an alternative to use the costly Reynold stress model (RSM) for the rotating pipe simulation and the SST k-ω model for the impingement. Findings The addition of swirl by means of a rotating pipe with a swirl intensity ranging from 0 up to 0.5 affects the velocity profiles, but has no remarkable effect on the spreading angle. The heat transfer is increased with respect to a non-swirling flow only at short nozzle-to-plate distances H/D < 6, where H is the distance and D is the diameter of the pipe. For the impinging zone, the highest average heat transfer is achieved at H/D = 5 with swirl intensity S = 0.5. This is the highest swirl studied in this work. Research limitations/implications High-fidelity simulations or experimental analysis may provide reliable data for higher swirl intensities, which are not covered in this work. Practical implications This two-step approach and the data provided is of interest to other related investigations (e.g. using arrays of jets or other surfaces than flat plates). Originality/value This paper is the first of its kind RANS simulation of the heat transfer from a flat plate to a swirling impinging jet flow issuing from a rotating pipe. An extensive study of these computational fluid dynamics (CFD) simulations has been carried out with the emphasis of splitting the large domain into two parts to facilitate the use of different turbulent models and periodic boundary conditions for the flow confined in the pipe.
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Portal-Porras, Koldo, Unai Fernandez-Gamiz, Iñigo Aramendia, Daniel Teso-Fz-Betoño, and Ekaitz Zulueta. "Testing the Accuracy of the Cell-Set Model Applied on Vane-Type Sub-Boundary Layer Vortex Generators." Processes 9, no. 3 (March 11, 2021): 503. http://dx.doi.org/10.3390/pr9030503.
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Vortex Generators (VGs) are applied before the expected region of separation of the boundary layer in order to delay or remove the flow separation. Although their height is usually similar to that of the boundary layer, in some applications, lower VGs are used, Sub-Boundary Layer Vortex Generators (SBVGs), since this reduces the drag coefficient. Numerical simulations of sub-boundary layer vane-type vortex generators on a flat plate in a negligible pressure gradient flow were conducted using the fully resolved mesh model and the cell-set model, with the aim on assessing the accuracy of the cell-set model with Reynolds-Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) turbulence modelling techniques. The implementation of the cell-set model has supposed savings of the 40% in terms of computational time. The vortexes generated on the wake behind the VG; vortical structure of the primary vortex; and its path, size, strength, and produced wall shear stress have been studied. The results show good agreements between meshing models in the higher VGs, but slight discrepancies on the lower ones. These disparities are more pronounced with LES. Further study of the cell-set model is proposed, since its implementation entails great computational time and resources savings.
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Wood, Brian D., Xiaoliang He, and Sourabh V. Apte. "Modeling Turbulent Flows in Porous Media." Annual Review of Fluid Mechanics 52, no. 1 (January 5, 2020): 171–203. http://dx.doi.org/10.1146/annurev-fluid-010719-060317.
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Turbulent flows in porous media occur in a wide variety of applications, from catalysis in packed beds to heat exchange in nuclear reactor vessels. In this review, we summarize the current state of the literature on methods to model such flows. We focus on a range of Reynolds numbers, covering the inertial regime through the asymptotic turbulent regime. The review emphasizes both numerical modeling and the development of averaged (spatially filtered) balances over representative volumes of media. For modeling the pore scale, we examine the recent literature on Reynolds-averaged Navier–Stokes (RANS) models, large-eddy simulation (LES) models, and direct numerical simulations (DNS). We focus on the role of DNS and discuss how spatially averaged models might be closed using data computed from DNS simulations. A Darcy–Forchheimer-type law is derived, and a prior computation of the permeability and Forchheimer coefficient is presented and compared with existing data.
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Strokach, Evgenij, Igor Borovik, and Fang Chen. "Numerical simulation of reacting flow in the combustion chamber and study of the impact of turbulent diffusion coefficients." Advances in Mechanical Engineering 12, no. 9 (September 2020): 168781402095497. http://dx.doi.org/10.1177/1687814020954974.
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A methodology for combustion modeling with complex mixing and thermodynamic conditions, especially in thrusters, is still under development. The resulting flow and propulsion parameters strongly depend on the models used, especially on the turbulence model as it determines the mixing efficiency. In this paper, the effect of the sigma-type turbulent diffusion coefficients arriving in the diffusion term of the turbulence model is studied. This study was performed using complex modeling, considering the conjugate effect of several physical phenomena such as turbulence, chemical reactions, and radiation heat transfer. To consider the varying turbulent Prandtl, an algebraic model was implemented. An adiabatic steady diffusion Flamelet approach was used to model chemical reactions. The P1 differential model with a WSGG spectral model was used for radiation heat transfer. The gaseous oxygen (GOX) and methane (GCH4) operating thruster developed at the Chair of turbomachinery and Flight propulsion of the Technical University of Munich (TUM) is taken as a test case. The studies use the 3D RANS approach using the 60° sector as the modeling domain. The normalized and absolute pressures, the integral and segment averaged heat flux are compared to numerical results. The wall heat fluxes and pressure distributions show good agreement with the experimental data, while the turbulent diffusion coefficients mostly influence the heat flux.
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Goeing, Jan, Hendrik Seehausen, Vladislav Pak, Sebastian Lueck, Joerg R. Seume, and Jens Friedrichs. "Influence of combined compressor and turbine deterioration on the overall performance of a jet engine using RANS simulation and Pseudo Bond Graph approach." Journal of the Global Power and Propulsion Society 4 (December 22, 2020): 296–308. http://dx.doi.org/10.33737/jgpps/131109.
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In this study, numerical models are used to analyse the influence of isolated component deterioration as well as the combination of miscellaneous deteriorated components on the transient performance of a high-bypass jet engine. For this purpose, the aerodynamic impact of major degradation effects in a high-pressure compressor (HPC) and turbine (HPT) is modelled and simulated by using 3D CFD (Computational Fluid Dynamics). The impact on overall jet engine performance is then modelled using an 1D Reduced Order Model (ROM). Initially, the HPC performance is investigated with a typical level of roughness on vanes and blades and the HPT performance with an increasing tip clearance. Subsequently, the overall performance of the jet engines with the isolated and combined deteriorated domains is computed by the in-house 1D performance tool ASTOR (AircraftEngine Simulation for Transient Operation Research). Degradations have a significant influence on the system stability and transient effects. In ASTOR, a system of differential equations including the equations of motion and further ordinary differential equations is solved. Compared to common ROMs, this enables a higher degree of accuracy. The results of temperature downstream of the high-pressure compressor and low-pressure turbine as well as the specific fuel composition and the HP rotational speed are used to estimate the degree and type of engine deterioration. However, the consideration of the system stability is necessary to analyse the characterisation in more detail. Finally, a simplified model which merges two engines with individual deteriorated domains into one combined deteriorated engine, is proposed. The simplified model predicts the performance of an engine which has been simulated with combined deteriorated components.
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Hosseinzadeh, Azin, and Amir Keshmiri. "Computational Simulation of Wind Microclimate in Complex Urban Models and Mitigation Using Trees." Buildings 11, no. 3 (March 11, 2021): 112. http://dx.doi.org/10.3390/buildings11030112.
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Due to a rapid increase in urbanisation, accurate wind microclimate assessment is of crucial importance. Evaluating wind flows around buildings is part of the planning application process in the design of new developments. In this study, computational fluid dynamics (CFD) simulations are carried out for a case study, representing the East Village in the London Olympic Park. Following a validation test against experimental data for a simpler urban configuration, the key input parameters, including appropriate boundary conditions, mesh setting and type of turbulence model, are selected for the Olympic Park model. All the simulations are conducted using the commercial code STARCCM+ under steady-state conditions with the Reynolds-averaged Navier–Stokes (RANS) method. The turbulence is modelled using different common variants of eddy-viscosity models (EVMs) including standard k-ε, realizable k-ε and standard and shear stress transport (SST) k-ω. The results demonstrate that standard and realisable k-ε models correlate very well with the experimental data, while some discrepancies are found with standard and SST k-ω. Following the determination of areas of high velocity, appropriate tree planting is proposed to overcome the effect of corner and downwash acceleration. With the optimised arrangement of trees and using specific types of tree (e.g., birch), wind speeds at the pedestrian level are reduced by 3.5, 25 and 66% in three main regions of interest. Moreover, we investigate the effects of tree heights. The obtained results illustrate that the wind velocity reduces when the crowns of the trees are located closer to the buildings and the ground. Our high-resolution CFD simulation and results offer a quantitative tool for wind microclimate assessment and optimised design and arrangement of trees around buildings to improve pedestrian comfort.
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Driss, Zied, Ghazi Bouzgarrou, Hedi Kchaou, and Mohamed Salah Abid. "Simulation numérique de l’écoulement laminaire induit dans des cuves agitées générées par les mobiles de proximité de type mono et double vis à profils simple et modifié." Mécanique & Industries 12, no. 2 (2011): 109–21. http://dx.doi.org/10.1051/meca/2011011.
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Yuan, Jianping, Yang Chen, Longyan Wang, Yanxia Fu, Yunkai Zhou, Jian Xu, and Rong Lu. "Dynamic Analysis of Cavitation Tip Vortex of Pump-Jet Propeller Based on DES." Applied Sciences 10, no. 17 (August 29, 2020): 5998. http://dx.doi.org/10.3390/app10175998.
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When a pump-jet propeller rotates at high speeds, a tip vortex is usually generated in the tip clearance region. This vortex interacts with the main channel fluid flow leading to the main energy loss of the rotor system. Moreover, operating at a high rotational speed can cause cavitation near the blades which may jeopardize the propulsion efficiency and induce noise. In order to effectively improve the propulsion efficiency of the pump-jet propeller, it is mandatory to research more about the energy loss mechanism in the tip clearance area. Due to the complex turbulence characteristics of the blade tip vortex, the widely used Reynolds averaged Navier–Stokes (RANS) method may not be able to accurately predict the multi-scale turbulent flow in the tip clearance. In this paper, an unsteady numerical simulation was conducted on the three-dimensional full flow field of a pump-jet propeller based on the DES (detached-eddy-simulation) turbulence model and the Z-G-B (Zwart–Gerber–Belamri) cavitation model. The simulation yielded the vortex shape and dynamic characteristics of the vortex core and the surrounding flow field in the tip clearance area. After cavitation occurred, the influence of cavitation bubbles on tip vortices was also studied. The results revealed two kinds of vortices in the tip clearance area, namely tip leakage vortex (TLV) and tip separation vortex (TSV). Slight cavitation at J = 1.02 led to low-frequency and high-frequency pulsation in the TLV vortex core. This occurrence of cavitation promotes the expansion and contraction of the tip vortex. Further, when the advance ratio changes into J = 0.73, a third type of vortex located between TLV and TSV appeared at the trailing edge which runs through the entire rotational cycle. This study has presented the dynamic characteristics of tip vortex including the relationship between cavitation bubbles and TLV inside the pump-jet propeller, which may provide a reference for the optimal design of future pump-jet propellers.
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Li, Chen, Hongming Wang, and Peiting Sun. "Numerical Investigation of a Two-Element Wingsail for Ship Auxiliary Propulsion." Journal of Marine Science and Engineering 8, no. 5 (May 9, 2020): 333. http://dx.doi.org/10.3390/jmse8050333.
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The rigid wingsail is a new type of propulsion equipment which greatly improves the performance of the sailboat under the conditions of upwind and downwind. However, such sail-assisted devices are not common in large ships because the multi-element wingsail is sensitive to changes in upstream flow, making them difficult to operate. This problem shows the need for aerodynamic study of wingsails. A model of two-element wingsail is established and simulated by the steady and unsteady RANS approach with the k-ω SST turbulence model and compared with the known experimental data to ensure the accuracy of the numerical simulation. Then, some key design and structural parameters (camber, the rotating axis position of the flap, angle of attack, flap thickness) are used to characterize the aerodynamic characteristics of the wingsail. The results show that the position of the rotating shaft of the flap has little influence on the lift coefficient at low camber. When stall occurs, the lift coefficient first increases and then decreases as the flap axis moves backward, which also delays the stall angle at a low camber. At the high camber of AOA = 6°, the lift coefficient always increases with the increase of the rotating axis position of the flap; especially between 85% and 95%, the lift coefficient increases suddenly, which is caused by the disappearance of large-scale flow separation on the suction surface of the flap. It reflects the nonlinear coupling effect between camber of wingsail and the rotating axis position of the flap
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Huang, Zongliu, Guangtai Shi, Xiaobing Liu, and Haigang Wen. "Effect of Flow Rate on Turbulence Dissipation Rate Distribution in a Multiphase Pump." Processes 9, no. 5 (May 18, 2021): 886. http://dx.doi.org/10.3390/pr9050886.
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The turbulence dissipation will cause the increment of energy loss in the multiphase pump and deteriorate the pump performance. In order to research the turbulence dissipation rate distribution characteristics in the pressurized unit of the multiphase pump, the spiral axial flow type multiphase pump is researched numerically in the present study. This research is focused on the turbulence dissipation rate distribution characteristics in the directions of inlet to outlet, hub to rim, and in the circumferential direction of the rotating impeller blades. Numerical simulation based on the RANS (Reynolds averaged Navier–Stokes equations) and the k-ω SST (Shear Stress Transport) turbulence model has been carried out. The numerical method is verified by comparing the numerical results with the experimental data. Results show that the regions of the large turbulence dissipation rate are mainly at the inlet and outlet of the rotating impeller and static impeller, while it is almost zero from the inlet to the middle of outlet in the suction surface and pressure surface of the first-stage rotating impeller blades. The turbulence dissipation rate is increased gradually from the hub to the rim of the inlet section of the first-stage rotating impeller, while it is decreased firstly and then increased on the middle and outlet sections. The turbulence dissipation rate distributes unevenly in the circumferential direction on the outlet section. The maximum value of the turbulence dissipation rate occurs at 0.9 times of the rated flow rate, while the minimum value at 1.5 times of the rated flow rate. Four turning points in the turbulence dissipation rate distribution that are the same as the number of impeller blades occur at 0.5 times the blade height at 0.9 times the rated flow rate condition. The turbulence dissipation rate distribution characteristics in the pressurized unit of the multiphase pump have been studied carefully in this paper, and the research results have an important significance for improving the performance of the multiphase pump theoretically.
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Carretta, Yves, Romain Boman, Nicolas Legrand, Maxime Laugier, and J. P. Ponthot. "Numerical Simulations of Asperity Crushing Using Boundary Conditions Encountered in Cold-Rolling." Key Engineering Materials 554-557 (June 2013): 850–57. http://dx.doi.org/10.4028/www.scientific.net/kem.554-557.850.
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The general framework of this paper is in the field of numerical simulation of asperity crushing. Different material forming processes, such as strip-rolling and deep drawing, imply mixed lubrication. In this lubrication regime, two types of contact are present at the same time: a direct contact between the two solids at the asperity level and also valleys filled with pressurized oil. Theses contact conditions have a large influence on friction and wear taking place during the upsetting process. As this mixed type of contact is not yet fully understood from the physics point of view, numerical models are essential to achieve a better understanding. For example, semi-analytical asperity crushing models have been developed by Wilson&Sheu [1] and Sutcliffe [2] to take into account the influence of bulk plastic deformations on asperity crushing. The finite element method has also been used to model asperity crushing. Ike&Makinouchi [3] studied the behavior of 2D triangular-shaped asperities under different boundary conditions. Krozekwa et al. [4] modeled 3D triangular asperities behavior, for various bulk strain directions. More recently, Lu et al. [5] compared experimental results of pyramid-shaped asperity and ridge-shaped asperity crushing with finite element simulation results. As in the three former references mentioned above, it has been decided, to study the interaction between a rigid plane and a simplified geometry asperity without lubricant. In this article, numerical asperity crushing results obtained with Metafor[6], a home made large strains software, will be presented. Those results will illustrate the influence of boundary conditions, contact pressure, large bulk strain and geometry of asperities on the evolution of the contact area. As the asperity crushing behaviour is known to be very sensitive to the boundary conditions, in this article, we will also present results using boundary conditions from a cold rolling model named MetaLub. MetaLub [7-8] is a software developed at the University of Liege in partnership with ArcelorMittal R&D center. It iteratively solves the equations resulting from the discretisation using the slab method of the strip coupled to a mixed lubrication model at the interface. This lubrication model takes into account the evolution of the oil film thickness as well as the asperity crushing along the roll bite. We will compare the evolution of the relative contact area obtained with MetaLub to the results obtained with finite elements simulations using the same boundary conditions. [1] Wilson, W.R.D and Sheu, S. Real area of contact and boundary friction in metal forming. Int. J. Mech. Sci. 1988, 30(7), 475-489. [2] Sutcliffe, M.P.F Surface asperity deformation in metal forming processes. Int. J. Mech. Sci., 1988, 30(11), 847-868. [3] Ike, H. and Makinouchi, A. Effect of lateral tension and compression on plane strain flattening processes of surface asperities lying over a plastically deformable bulk. Wear, 1990, 140, 17-38. [4] Korzekwa, D.A., Dawson, P.R. and Wilson W.R.D., Surface asperity deformation during sheet forming. Int. J. Mech. Sci., 1992, 34(7), 521-539. [5] Lu, C., Wei, D., Jiang, Z., and Tieu, K., Experimental and theoretical investigation of the asperity flattening process under large bulk strain, Proc. Inst. Mech. Eng. J. 222 (2008), 271–278. [6] LTAS-MN2L. ULg. http://metafor.ltas.ulg.ac.be/. [7] Stéphany, A., Contribution à l’étude numérique de la lubrification en régime mixte en laminage à froid. PhD dissertation (in French), Université de Liège (2008) [8] Carretta, Y., Stephany, A., Legrand, N., Laugier, M., and Ponthot, J.-P., MetaLub – A slab method software for the numerical simulation of mixed lubrication regime. Application to cold rolling. In Proceedings of the 4th International Conference on Tribology In Manufacturing Processes (ICTMP), 2010,799-808.
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Tyacke, James, Paul Tucker, Richard Jefferson-Loveday, Nagabushana Rao Vadlamani, Robert Watson, Iftekhar Naqavi, and Xiaoyu Yang. "Large Eddy Simulation for Turbines: Methodologies, Cost and Future Outlooks." Journal of Turbomachinery 136, no. 6 (November 19, 2013). http://dx.doi.org/10.1115/1.4025589.
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Flows throughout different zones of turbines have been investigated using large eddy simulation (LES) and hybrid Reynolds-averaged Navier–Stokes-LES (RANS-LES) methods and contrasted with RANS modeling, which is more typically used in the design environment. The studied cases include low and high-pressure turbine cascades, real surface roughness effects, internal cooling ducts, trailing edge cut-backs, and labyrinth and rim seals. Evidence is presented that shows that LES and hybrid RANS-LES produces higher quality data than RANS/URANS for a wide range of flows. The higher level of physics that is resolved allows for greater flow physics insight, which is valuable for improving designs and refining lower order models. Turbine zones are categorized by flow type to assist in choosing the appropriate eddy resolving method and to estimate the computational cost.
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Yao, Jixian, Steven E. Gorrell, and Aspi R. Wadia. "High-Fidelity Numerical Analysis of Per-Rev-Type Inlet Distortion Transfer in Multistage Fans—Part II: Entire Component Simulation and Investigation." Journal of Turbomachinery 132, no. 4 (May 6, 2010). http://dx.doi.org/10.1115/1.3148479.
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Part I of this paper validated the ability of the unsteady Reynolds-Averaged Navier-Stokes (RANS) solver PTURBO to accurately simulate distortion transfer and generation through selected blade rows of two multistage fans. In this part, unsteady RANS calculations were successfully applied to predict the 1/rev inlet total pressure distortion transfer in the entirety of two differently designed multistage fans. This paper demonstrates that high-fidelity computational fluid dynamics (CFD) can be used early in the design process for verification purposes before hardware is built and can be used to reduce the number of distortion tests, hence reducing engine development cost. The unsteady RANS code PTURBO demonstrated remarkable agreement with the data, accurately capturing both the magnitude and the profile of total pressure and total temperature measurements. Detailed analysis of the flow physics identified from the CFD results has led to a thorough understanding of the total temperature distortion generation and transfer mechanism, especially for the spatial phase difference of total pressure and total temperature profiles. The analysis illustrates that the static parameters are more revealing than their stagnation counterpart and that pressure and temperature rise are more revealing while the pressure and temperature ratio could be misleading. The last stage is effectively throttled by the inlet distortion even though the overall engine throttle remains unchanged. The total temperature distortion generally grows as flow passes through the fan stages.
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El Dabaghi, F., A. El Kacimi, and B. Nakhlé. "Flood simulation via shallow water numerical model based on characteristic method." Revue Africaine de la Recherche en Informatique et Mathématiques Appliquées Volume 5, Special Issue TAM... (October 7, 2006). http://dx.doi.org/10.46298/arima.1874.
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International audience This work deals with the numerical simulation of flood waves propagation. This phenomena can be described by the non conservative form of shallow water or St-Venant equations, in water velocity-depht formulation (u,H). The numerical approximation of the model is based on the Characteristics method for the time discretization. The obtained steady system is of Quasi-Stokes type, and it is resolved by a preconditioned Uzawa conjugated gradient algorithm, combined to P1/P1 finite element for the spatial approximation. Some numerical results describing subcritical flow on various fluid domains are given. Ce travail concerne la simulation numérique de la propagation des crues. Ce phénomène peut être décrit par les équations d'eau peu profonde ou de Saint-Venant, écrites sous forme non conservative en formulation vitesse-hauteur (u,H). L'approximation numérique du modèle repose sur la méthode des caractéristiques pour la discrétisation temporelle. Le système stationnaire obtenu est de type Quasi-Stokes, et il est résolu par un algorithme de gradient conjugué Uzawa préconditionné, basé sur la méthode des éléments finis P1/P1 pour l'approximation spatiale. Des résultats numériques concernant des simulations d'écoulements subcritiques dans plusieurs type de conduites sont présentés.
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Mikuž, Blaž, and Ferry Roelofs. "Flow and Heat Transfer Simulation in a Complete PWR Fuel Assembly Using Wall-Modelled Rans." Journal of Nuclear Engineering and Radiation Science, June 11, 2021. http://dx.doi.org/10.1115/1.4051446.
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Abstract Reproduction of turbulent flow and heat transfer inside a pressurized water reactor (PWR) fuel assembly is a challenging task due to the complex geometry and the huge computational domain. Capability of a wall-modelled RANS approach has been examined, which had already been validated against the measurements of the MATiS-H experiment. The method is here expanded to a larger computational domain aiming to reproduce flow and thermal field in the entire PWR fuel assembly. Namely, in the first part of the present study, wall-modelled RANS is performed in a relatively short section of the representative PWR fuel assembly containing one single mixing grid with an array of 15×15 fuel rods. Linear and nonlinear eddy-viscosity turbulence models have been applied, however no significant difference is observed in the predicted pressure drop in the fuel assembly. The obtained predictions revealed an interesting pattern of swirl flow as well as diagonal cross flow downstream the mixing grid, which is driven by the applied design of split-type mixing vanes. In the second part, the computational model is extended to a domain representative of a complete PWR fuel assembly with ten mixing grids, inlet and outlet sections. Pressure drop and flow field are analysed together with the predicted temperature and potential hot spots. In spite of a relatively coarse spatial resolution of the applied approach, the wall-modelled RANS provided promising results at least for the qualitative prediction of the pressure, flow field and location of hot spots.
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Vilkinis, Paulius, Nerijus Pedišius, and Mantas Valantinavičius. "Investigation of Flow Dynamics Over Transitional-Type Microcavity." Journal of Fluids Engineering 140, no. 7 (March 13, 2018). http://dx.doi.org/10.1115/1.4039159.
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Flow over a transitional-type cavity in microchannels is studied using a microparticle image velocimetry system (μPIV) and commercially available computational fluid dynamics (CFD) software in laminar, transitional, and turbulent flow regimes. According to experimental results, in the transitional-type cavity (L/h1 = 10) and under laminar flow in the channel, the recirculation zone behind the backward-facing step stretches linearly with ReDh until the reattachment point reaches the middle of the cavity at xr/L = (0.5 to 0.6). With further increase in ReDh, the forward-facing step lifts the reattaching flow from the bottom of the cavity and stagnant recirculation flow fills the entire space of the cavity. Flow reattachment to the bottom of the cavity is again observed only after transition to the turbulent flow regime in the channel. Reynolds-averaged Navier–Stokes (RANS) equations and large eddy simulation (LES) results revealed changes in vortex topology, with the flow regime changing from laminar to turbulent. During the turbulent flow regime in the recirculation zone, periodically recurring vortex systems are formed. Experimental and computational results have a good qualitative agreement regarding the changes in the flow topology. However, the results of numerical simulations based on RANS equations and the Reynolds-stress-baseline turbulence model (RSM-BSL), show that computed reattachment length values overestimate the experimentally obtained values. The RSM-BSL model underestimates the turbulent kinetic energy intensity, generated by flow separation phenomena, on the stage of transitional flow regime.
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Kumar, Aishvarya, Ali Ghobadian, and Jamshid Nouri. "Numerical simulation and experimental validation of cavitating flow in a multi-hole diesel fuel injector." International Journal of Engine Research, February 22, 2021, 146808742199863. http://dx.doi.org/10.1177/1468087421998631.
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This study assesses the predictive capability of the ZGB (Zwart-Gerber-Belamri) cavitation model with the RANS (Reynolds Averaged Navier-Stokes), the realizable k-epsilon turbulence model, and compressibility of gas/liquid models for cavitation simulation in a multi-hole fuel injector at different cavitation numbers (CN) for diesel and biodiesel fuels. The prediction results were assessed quantitatively by comparison of predicted velocity profiles with those of measured LDV (Laser Doppler Velocimetry) data. Subsequently, predictions were assessed qualitatively by visual comparison of the predicted void fraction with experimental CCD (Charged Couple Device) recorded images. Both comparisons showed that the model could predict fluid behavior in such a condition with a high level of confidence. Additionally, flow field analysis of numerical results showed the formation of vortices in the injector sac volume. The analysis showed two main types of vortex structures formed. The first kind appeared connecting two adjacent holes and is known as “hole-to-hole” connecting vortices. The second type structure appeared as double “counter-rotating” vortices emerging from the needle wall and entering the injector hole facing it. The use of RANS proved to save significant computational cost and time in predicting the cavitating flow with good accuracy.
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Gaggero, S. "RIM DRIVEN PROPELLERS: OPTIMIZATION BASED DESIGN APPROACH USING RANS CALCULATIONS." Propellers & Impellers: Research, Design, Construction and Application, March 28, 2019. http://dx.doi.org/10.3940/rina.pro.2019.05.
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RIM driven propellers represent an unconventional, but underrated, propulsive solution which hydrodynamic design is still not obvious. In the last years, most of the attention has been devoted to the efficient coupling with electric motors, since only recently the development of permanent magnets allowed for the successful embedding of the driver directly inside the surrounding duct. From the hydrodynamic point of view, however, analysis and, in particular, design strategies are not yet ripe. In the light of the development of advanced design approaches for unconventional geometries, we propose a Simulation-Based Design Optimization tool based on RANS analyses of parametrically described geometries as a part of an automatic, multi-objective optimization loop. The SBDO is used to design a RIM driven propeller with an accelerating type duct, with improved performance simultaneously in terms both of efficiency and cavitation inception at different (design and quasi-bollard pull) functioning conditions.
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Joung, Daero, and Kang Y. Huh. "3D RANS Simulation of Turbulent Flow and Combustion in a 5 MW Reverse-Flow Type Gas Turbine Combustor." Journal of Engineering for Gas Turbines and Power 132, no. 11 (August 11, 2010). http://dx.doi.org/10.1115/1.4000894.
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This study is concerned with 3D RANS simulation of turbulent flow and combustion in a 5 MW commercial gas turbine combustor. The combustor under consideration is a reverse flow, dry low NOx type, in which methane and air are partially mixed inside swirl vanes. We evaluated different turbulent combustion models to provide insights into mixing, temperature distribution, and emission in the combustor. Validation is performed for the models in STAR-CCM+ against the measurement data for a simple swirl flame (http://public.ca.sandia.gov/TNF/swirlflames.html). The standard k-ε model with enhanced wall treatment is employed to model turbulent swirl flow, whereas eddy break-up (EBU), presumed probability density function laminar flamelet model, and partially premixed coherent flame model (PCFM) are tried for reacting flow in the combustor. Independent simulations are carried out for the main and pilot nozzles to avoid flashback and to provide realistic inflow boundary conditions for the combustor. Geometrical details such as air swirlers, vane passages, and liner holes are all taken into account. Tested combustion models show similar downstream distributions of the mean flow and temperature, while EBU and PCFM show a lifted flame with stronger effects of swirl due to limited increase in axial momentum by expansion.
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Li, Jiajia, Ben Yuan, and Pablo M. Carrica. "Modeling Bubble Entrainment and Transport for Ship Wakes: Progress Using Hybrid RANS/LES Methods." Journal of Ship Research, 2019. http://dx.doi.org/10.5957/josr.09180071.
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This article presents progress on modeling bubble entrainment and transport around ships using hybrid Reynolds-averaged Navier–Stokes/large eddy simulation (RANS/LES) methods. Previous results using a Boltzmann-based polydisperse bubbly flow model show that LES perform better than RANS in predicting transport of bubbles to depth, a very important process to predict bubbly wakes. However, standard DES-type models fail to predict proper turbulent kinetic energy (TKE) and dissipation, needed by bubble entrainment, breakup, and coalescence models. We propose different approaches to obtain TKE and dissipation in LES regions and evaluate them for cases of increasing complexity, including decay of isotropic turbulence, a flat plate boundary layer, and the flow in the wake of the research vessel Athena. An exponential weighted average is used to estimate statistics and obtain the averaged quantities in regions with resolved turbulence. The TKE is satisfactorily predicted in the cases tested. A modified #x03C9; equation in the SST model is proposed to implicitly compute the dissipation, showing superior results than the standard DES models, although further improvements are necessary. A hybrid RANS/LES approach is proposed, which focused at conserving total TKE as the flow crosses RANS/LES interfaces, as previously performed for zonal approaches but attempting a DES-like detection of regions suitable for LES, critical for large-scale computations of bubbly flows involving complex geometries. A general form of a dynamic forcing term is derived to transfer the modeled TKE to resolved TKE with a controller to guarantee proper conservation of the energy transferred. It was verified that the model is not sensitive to grid size or time step. Improvements to DDES and the proposed TKE-conserving hybrid RANS/LES method show encouraging results, although remaining challenges are discussed.