The Experts below are selected from a list of 204 Experts worldwide ranked by ideXlab platform
Bohuš Kysela - One of the best experts on this subject based on the ideXlab platform.
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Local velocity scaling in upward flow to tooth impeller in a Fully Turbulent Region
EPJ Web of Conferences, 2019Co-Authors: Radek Šulc, I Fořt, Pavel Ditl, Darina Jasikova, Michal Kotek, Vaclav Kopecky, Bohuš KyselaAbstract:The hydrodynamics and flow field were measured in an agitated vessel using 2-D Time Resolved Particle Image Velocimetry (2-D TR PIV). The experiments were carried out in a Fully baffled cylindrical flat bottom vessel 400 mm in inner diameter agitated by a tooth impeller 133 mm in diameter. Distilled water was used as the agitated liquid. The velocity fields were investigated in the upward flow to the impeller for three impeller rotation speeds – 300 rpm, 500 rpm and 700 rpm, corresponding to a Reynolds number in the range 94 000 < Re < 221 000. This means that Fully-developed Turbulent flow was reached. This Re range secures the Fully-developed Turbulent flow in an agitated liquid. In accordance with the theory of mixing, the dimensionless mean and fluctuation velocities in the measured directions were found to be constant and independent of the impeller Reynolds number. On the basis of the test results the spatial distributions of dimensionless velocities were calculated. The axial turbulence intensity was found to be in the majority in the range from 0.4 to 0.7, which corresponds to the middle level of turbulence intensity.
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Local velocity scaling in an impeller discharge flow in T400 vessel agitated by tooth impeller in a Fully Turbulent Region
EPJ Web of Conferences, 2018Co-Authors: Radek Šulc, I Fořt, Pavel Ditl, Darina Jasikova, Michal Kotek, Vaclav Kopecky, Bohuš KyselaAbstract:Hydrodynamics and flow field were measured in an agitated vessel using 2-D Time Resolved Particle Image Velocimetry (2-D TR PIV). The experiments were carried out in a Fully baffled cylindrical flat bottom vessel 400 mm in inner diameter agitated by a tooth impeller 133 mm in diameter. The velocity fields were measured in the impeller discharge flow for impeller rotation speeds from 300 rpm to 700 rpm and three liquids of different viscosities (i.e. (i) distilled water, ii) a 28% vol. aqueous solution of glycol, and iii) a 43% vol. aqueous solution of glycol), corresponding to the impeller Reynolds number in the range 68 000 < Re < 221 000. This Re range secures the Fully-developed Turbulent flow of agitated liquid. In accordance with the theory of mixing, the dimensionless mean and fluctuation velocities in the measured directions were found to be constant and independent of the impeller Reynolds number. On the basis of the test results the spatial distributions of dimensionless velocities were calculated. The radial turbulence intensity was found to be in the majority in the range from 0.3 to 0.9, which corresponds to the high level of this quantity.
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local velocity scaling in t400 vessel agitated by rushton turbine in a Fully Turbulent Region
EPJ Web of Conferences, 2017Co-Authors: Radek Šulc, I Fořt, Pavel Ditl, Darina Jasikova, Michal Kotek, Vaclav Kopecky, Bohuš KyselaAbstract:The hydrodynamics and flow field were measured in an agitated vessel using 2-D Time Resolved Particle Image Velocimetry (2-D TR PIV). The experiments were carried out in a Fully baffled cylindrical flat bottom vessel 400 mm in inner diameter agitated by a Rushton turbine 133 mm in diameter. The velocity fields were measured in the zone in upward flow to the impeller for impeller rotation speeds from 300 rpm to 850 rpm and three liquids of different viscosities (i.e. (i) distilled water, ii) a 28% vol. aqueous solution of glycol, and iii) a 43% vol. aqueous solution of glycol), corresponding to the impeller Reynolds number in the range 50 000 < Re < 189 000. This Re range secures the Fully-developed Turbulent flow of agitated liquid. In accordance with the theory of mixing, the dimensionless mean and fluctuation velocities in the measured directions were found to be constant and independent of the impeller Reynolds number. On the basis of the test results the spatial distributions of dimensionless velocities were calculated. The axial turbulence intensity was found to be in the majority in the range from 0.388 to 0.540, which corresponds to the high level of turbulence intensity.
Lars Davidson - One of the best experts on this subject based on the ideXlab platform.
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Natural convection boundary layer in a 5:1 cavity
Physics of Fluids, 2007Co-Authors: Darioush Gohari Barhaghi, Lars DavidsonAbstract:The natural convection boundary layer in a tall cavity with an aspect ratio of AR=5 is studied numerically. The Rayleigh number based on the width of the cavity is RaW=4.028×108. The large eddy simulation method together with different subgrid scale models are used to study the near-wall behavior of the boundary layer and the turbulence structure. It is found that the dynamic subgrid scale model is the most accurate model in terms of predicting the transition location. Results also indicate that the conventional grid resolutions expressed in viscous units that are used for forced convection flows are not appropriate in the case of the natural convection flows and higher grid resolutions are necessary. The turbulence statistics are studied in both the Turbulent and the transition Regions. Although the results of the Fully Turbulent Region show no important grid dependency, it is found that the accuracy of the results in the transition Region is highly grid dependent, suggesting that the subgrid scale fluct...
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Prediction of the Flow Around an Airfoil Using a Reynolds Stress Transport Model
Journal of Fluids Engineering, 1995Co-Authors: Lars DavidsonAbstract:A second-moment Reynolds Stress Transport Model (RSTM) is used in the present work for computing the flow around a two-dimensional airfoil. An incompressible SIMPLEC code is used, employing a non-staggered grid arrangement. A third-order QUICK scheme is used for the momentum equations, and a second-order, bounded MUSCL scheme is used for the Turbulent quantities. As the RSTM is valid only for Fully Turbulent flow, an eddy viscosity, one-equation model is used near the wall. The two models are matched along a preselected grid line in the Fully Turbulent Region. Detailed comparisons between calculations and experiments are presented for an angle of attack of α = 13.3 deg. The RSTM predictions agree well with the experiments, and approaching stall is predicted for α = 17 deg, which agrees well with experimental data. The results obtained with a two-layer k − e model show poor agreement with experimental data; the velocity profiles on the suction side of the airfoil show no tendency of separation, and no tendency of stall is predicted
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Reynolds stress transport modelling of shock-induced separated flow
Computers & Fluids, 1995Co-Authors: Lars DavidsonAbstract:Abstract Predicting the interaction process in transonic flow between the inviscid free stream and the Turbulent boundary layer is a challenging task for numerical simulation, which involves complex physical phenomena. In order to capture the physics, a turbulence model capable of accounting for physical phenomena such as streamline curvature, strong non-local effects and history effects, and large irrotational strains should be used. In the present work a second-moment Reynolds Stress Transport Model (RSTM) is used for computing transonic flow in a plane channel with a bump. An explicit time-marching Runge-Kutta code is used for the mean flow equations. The convecting terms are discretized using a third-order scheme (QUICK), and no explicit dissipation is added. For solving the transport equations for the Reynolds stresses u 2 , v 2 , and uv as well as k and ϵ an implicit solver is used which—unlike the Runge-Kutta solver—proved to be very stable and reliable for solving source dominated equations. Second-order discretization schemes are used for the convective terms. As the RSTM is valid only for Fully Turbulent flow, a one-equation model is used near the wall. The two models are matched along a pre-selected grid line in the Fully Turbulent Region. The agreement between predictions and measurements is, in general, good.
Greg F. Naterer - One of the best experts on this subject based on the ideXlab platform.
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Near-wall velocity profile with adaptive shape functions for Turbulent forced convection☆
International Communications in Heat and Mass Transfer, 2005Co-Authors: P.s. Glockner, Greg F. NatererAbstract:Abstract This article applies Reichardt's velocity profile to Turbulent convection analysis. In contrast to a conventional law-of-the-wall formulation with three Regions, a single profile represents the entire Region from the viscous sublayer to the Fully Turbulent Region. Special shape functions are developed for this profile in a hybrid finite element/volume formulation, together with dissipation rate boundary conditions, which are consistent with the velocity profile modeling. Applications to Turbulent channel flow are successFully predicted with a k − ɛ turbulence model.
Suo Shuangfu - One of the best experts on this subject based on the ideXlab platform.
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Numerical Study of the Plasma Region of High Velocity Wire-Arc Spray
China Surface Engineering, 2006Co-Authors: Suo ShuangfuAbstract:With the application of Fluent, the jet flow field of a wire-arc spraying gun was simulated and computed, which could be characterized by four Regions: plasma Region, core Region, entrainment Region and the Fully Turbulent Region. The results showed that the plasma Region had very limited effect on the other Regions. It only caused 20~40 degree rising of the temperature on the axis of jet flow. But in the plasma Region itself, the velocity and temperature were severely fluctuated, up to 1 600 m/s and 6 800 K respectively. From anode to cathode, the average temperature was gradually reduced from 4250 K to 538 K.
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Studies of Computational Fluid Dynamics in the Flow Field of a High Velocity Wire Arc Spray Gun
China Surface Engineering, 2005Co-Authors: Suo ShuangfuAbstract:The fluid dynamics in the jet field of a high velocity wire arc spray gun is one of the key factors to coating qualities. With the application of Fluent, the jet flow dynamics of a spray gun is simulated and computed, which concludes that the jet field could be characterized by three Regions: the core Region, the entrainment Region, and the Fully Turbulent Region. Influenced by the intersecting and reflecting of shock waves, the velocity distribution of the jet is non-homogeneous and asymmetric, and the axis velocity is severely fluctuated. Moreover, The flow in the wire plane is more divergent than that in the wires’ vertical plane. Therefore, it’s an important way to improve spray quality with appropriate spray distance and a special designed cap.
John L. Lumley - One of the best experts on this subject based on the ideXlab platform.
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Turbulence measurements in axisymmetric jets of air and helium. I - Air jet. II - Helium jet
Journal of Fluid Mechanics, 1993Co-Authors: N. R. Panchapakesan, John L. LumleyAbstract:A Turbulent round jet of air discharging into quiescent air was studied experimentally. Some × -wire hot-wire probes mounted on a moving shuttle were used to eliminate rectification errors due to flow reversals in the intermittent Region of the jet. Moments of velocity fluctuations up to fourth order were measured to characterize Turbulent transport in the jet and to evaluate current models for triple moments that occur in the Reynolds stress equations. Fourth moments were very well described in terms of second moments by the quasi-Gaussian approximation across the entire jet including the intermittent Region. Profiles of third moments were found to be significantly different from earlier measurements: 〈uv2〉, 〈uw2〉 and 〈u2v〉 are found to be negative near the axis of the jet. The Basic triple moment model that included Turbulent production and models for the dissipation and the return-to-isotropy part of the pressure correlations was found to be unsatisfactory. When mean-strain production and a model for rapid pressure correlations were also included, predictions were satisfactory in the Fully Turbulent Region. The consistency of the measurements with the equations of motion was assessed: momentum flux across the jet was found to be within ±5% of the nozzle input and the integral of radial diffusive flux of Turbulent kinetic energy across the jet calculated from the measured third moments was found to be close to zero.
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Turbulence measurements in axisymmetric jets of air and helium. Part 2. Helium jet
Journal of Fluid Mechanics, 1993Co-Authors: N. R. Panchapakesan, John L. LumleyAbstract:A Turbulent round jet of helium was studied experimentally using a composite probe consisting of an interference probe of the Way–Libby type and an × -probe. Simultaneous measurements of two velocity components and helium mass fraction concentration were made in the x/d range 50–120. These measurements are compared with measurements in an air jet of the same momentum flux reported in Part 1. The jet discharge Froude number was 14000 and the measurement range was in the intermediate Region between the non-buoyant jet Region and the plume Region. The measurements are consistent with earlier studies on helium jets. The mass flux of helium across the jet is within ±10% of the nozzle input. The mean velocity field along the axis of the jet is consistent with the scaling expressed by the effective diameter but the mean concentration decay constant exhibits a density-ratio dependence. The radial profiles of mean velocity and mean concentration agree with earlier measurements, with the half-widths indicating a Turbulent Schmidt number of 0.7. Significantly higher intensities of axial velocity fluctuations are observed in comparison with the air jet, while the intensities of radial and azimuthal velocity fluctuations are virtually identical with the air jet when scaled with the half-widths. Approximate budgets for the Turbulent kinetic energy, scalar variance and scalar fluxes are presented. The ratio of mechanical to scalar timescales is found to be close to 1.5 across most of the jet. Current models for triple moments involving scalar fluctuations are compared with measurements. As was observed with the velocity triple moments in Part 1, the performance of the Full model that includes all terms except advection was found to be very good in the Fully Turbulent Region of the jet.
