URANS Calculations for Smooth Circular Cylinder Flow in a Wide Range of Reynolds Numbers: Solution Verification and Validation

2012 ◽  
Vol 134 (12) ◽  
Author(s):  
Guilherme F. Rosetti ◽  
Guilherme Vaz ◽  
André L. C. Fujarra
Keyword(s):  
Large Range ◽  
Reynolds Numbers ◽  
Uncertainty Estimation ◽  
Wide Range ◽  
Modeling Errors ◽  
Solution Verification ◽  
Sst Turbulence Model ◽  
Validation Procedure ◽  
Cylinder Flow ◽  
Fixed Cylinder

The flow around circular smooth fixed cylinder in a large range of Reynolds numbers is considered in this paper. In order to investigate this canonical case, we perform CFD calculations and apply verification & validation (V&V) procedures to draw conclusions regarding numerical error and, afterwards, assess the modeling errors and capabilities of this (U)RANS method to solve the problem. Eight Reynolds numbers between Re = 10 and Re=5×105 will be presented with, at least, four geometrically similar grids and five discretization in time for each case (when unsteady), together with strict control of iterative and round-off errors, allowing a consistent verification analysis with uncertainty estimation. Two-dimensional RANS, steady or unsteady, laminar or turbulent calculations are performed. The original 1994 k-ω SST turbulence model by Menter is used to model turbulence. The validation procedure is performed by comparing the numerical results with an extensive set of experimental results compiled from the literature.

URANS Calculations for Smooth Circular Cylinder Flow in a Wide Range of Reynolds Numbers: Solution Verification and Validation

2012 ◽  
Author(s):  
Guilherme F. Rosetti ◽  
Guilherme Vaz ◽  
André L. C. Fujarra
Keyword(s):  
Large Range ◽  
Reynolds Numbers ◽  
Data Repository ◽  
Wide Range ◽  
Solution Verification ◽  
Sst Turbulence Model ◽  
Validation Procedure ◽  
Unsteady Rans ◽  
Cylinder Flow ◽  
Fixed Cylinder

The flow around circular smooth fixed cylinder in a large range of Reynolds numbers is considered in this paper. In order to investigate this canonical case, we perform CFD calculations and apply Verification & Validation (V&V) procedures to draw some conclusions regarding numerical error, and afterwards, assess the modelling errors and capabilities of URANS method to solve this problem. Eight Reynolds numbers between Re = 10 and Re = 5×105 will be presented with five geometrically similar grids and five time steps for each case, together with strict control of iterative and round-off errors, allowing a consistent verification analysis with uncertainty estimation. In these calculations, two-dimensional Unsteady RANS calculations were performed making use of the k–ω SST turbulence model. The Validation procedure is performed by comparing the numerical results with an extensive set of experimental results compiled from the literature and also made available in the VIV Data Repository website (http://oe.mit.edu/VIV/).

Modeling Transition for the Cylinder Flow With Verification and Validation

2015 ◽  
Author(s):  
Guilherme F. Rosetti ◽  
Guilherme Vaz ◽  
André L. C. Fujarra
Keyword(s):  
Turbulence Models ◽  
Reynolds Numbers ◽  
Verification And Validation ◽  
Transition Model ◽  
Physical Conditions ◽  
Turbulent Transition ◽  
Solution Verification ◽  
Sst Turbulence Model ◽  
High Reynolds ◽  
Cylinder Flow

The widespread use of Computational Fluid Dynamics (CFD) tools for engineering applications is certainly positive. However, users must also be aware of the physics of the problems being modeled, as well as the shortcomings of turbulence models in use. New state-of-the-art turbulence models are currently being developed with the aim of enhancing the turbulent flow predictions but the laminar-turbulent transition is still out of the scope of most the models. Bearing upon those ideas, this paper investigates the performance of the Local Correlation Transition Model (LCTM) for the cylinder flow with Solution Verification and Validation at high Reynolds numbers. Furthermore, attention is paid to characteristics of the setup, numerics and physical conditions and we study how these features alter the results. We also bring recommendations on the use of the transition model regarding grid, setup and physical conditions. The results show much better comparison of numerical and experimental results regarding drag coefficients than seen with the SST turbulence model, even with the two-dimensional calculations done herein.

Workshop on Verification and Validation of CFD for Offshore Flows

2012 ◽  
Author(s):  
L. Eça ◽  
G. Vaz
Keyword(s):  
Reynolds Numbers ◽  
Verification And Validation ◽  
Test Cases ◽  
Code Verification ◽  
Complex Flow ◽  
Solution Verification ◽  
Manufactured Solution ◽  
Cylinder Flow ◽  
Flow Case ◽  
Paper Submission

This document introduces the Workshop on Verification and Validation (V&V) of CFD for Offshore Flows, to be held during OMAE2012. It presents a brief introduction to the purpose of Verification and Validation with the identification of the goals of code and solution verification and validation. Within this context, three test-cases are proposed: Case-I of code verification, Case-II of solution verification and Case-III of solution verification and validation. Case-I consists on a 3D manufactured solution of an unsteady turbulent flow. Case-II is an exercise on the canonical problem of the infinite smooth circular cylinder flow at different Reynolds numbers. Case-III is a more complex flow around a straked-riser. The participants are asked to perform at least one of these test-cases. The objectives for the three proposed test-cases are presented, together with a detailed description of the numerical settings to be used, and the results to be obtained and sent to the Workshop organization. At the end some considerations on general conditions, paper submission, deadlines, and encouragements are stated.

On the Effects of Turbulence Modeling on the Fluid-Structure Interaction of a Rigid Cylinder

2016 ◽  
Author(s):  
Guilherme Feitosa Rosetti ◽  
Guilherme Vaz ◽  
André Luís Condino Fujarra
Keyword(s):  
Turbulence Modeling ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Reynolds Numbers ◽  
Boundary Layer Separation ◽  
Turbulent Transition ◽  
Moving Cylinder ◽  
Wide Range ◽  
Cylinder Flow ◽  
Laminar Turbulent Transition

The cylinder flow is a canonical problem for Computational Fluid Dynamics (CFD), as it can display several of the most relevant issues for a wide class of flows, such as boundary layer separation, vortex shedding, flow instabilities, laminar-turbulent transition and others. Several applications also display these features justifying the amount of energy invested in studying this problem in a wide range of Reynolds numbers. The Unsteady Reynolds Averaged Navier Stokes (URANS) equations combined with simplifying assumptions for turbulence have been shown inappropriate for the captive cylinder flow in an important range of Reynolds numbers. For that reason, recent improvements in turbulence modeling has been one of the most important lines of research within that issue, aiming at better prediction of flow and loads, mainly targeting the three-dimensional effects and laminar-turbulent transition, which are so important for blunt bodies. In contrast, a much smaller amount of work is observed concerning the investigation of turbulent effects when the cylinder moves with driven or free motions. Evidently, larger understanding of the contribution of turbulence in those situations can lead to more precise mathematical and numerical modeling of the flow around a moving cylinder. In this paper, we present CFD calculations in a range of moderate Reynolds numbers with different turbulence models and considering a cylinder in captive condition, in driven and in free motions. The results corroborate an intuitive notion that the inertial effects indeed play very important role in determining loads and motions. The flow also seems to adapt to the motions in such a way that vortices are more correlated and less influenced by turbulence effects. Due to good comparison of the numerical and experimental results for the moving-cylinder cases, it is observed that the choice of turbulence model for driven and free motions calculations is markedly less decisive than for the captive cylinder case.

Temporal analysis of capillary jet breakup

1995 ◽  
Vol 291 ◽  
pp. 163-190 ◽  
Author(s):  
N. Ashgriz ◽  
F. Mashayek
Keyword(s):  
Linear Theory ◽  
Large Range ◽  
Reynolds Numbers ◽  
Temporal Analysis ◽  
Liquid Jets ◽  
Breakup Mechanism ◽  
Jet Breakup ◽  
Satellite Drops ◽  
Wide Range ◽  
Breakup Time

The temporal instability of a cylindrical capillary jet is analysed numerically for different liquid Reynolds numbers Re, disturbance wavenumbers k, and amplitudes ε0. The breakup mechanism of viscous liquid jets and the formation of satellite drops are described. The results show that the satellite size decreases with decreasing Re, and increasing k and ε0. Marginal Reynolds numbers below which no satellite drops are formed are obtained for a large range of wavenumbers. The growth rates of the disturbances are calculated and compared with those from the linear theory. These results match for low-Re jets, however as Re is increased the results from the linear theory slightly overpredict those from the nonlinear analysis. (At the wavenumber of k = 0.9, the linear theory underpredicts the nonlinear results.) The breakup time is shown to decrease exponentially with increasing the amplitude of the disturbance. The cut-off wavenumber is shown to be strongly dependent on the amplitude of the initial disturbance for amplitudes larger than approximately $\frac13$ of the initial jet radius. The stable oscillations of liquid jets are also investigated. The results indicate that liquid jets with Re ∼ O(1) do not oscillate, and the disturbances are overdamped. However, liquid jets with higher Re oscillate with a period which depends on Re and ε0. The period of the oscillation decreases with increasing Re at small ε0; however, it increases with increasing Re at large ε0. Marginal Reynolds numbers below which the disturbances are overdamped are obtained for a wide range of wavenumbers and ε0 = 0.05.

Turbulent three-dimensional dielectric electrohydrodynamic convection between two plates

2012 ◽  
Vol 696 ◽  
pp. 228-262 ◽  
Author(s):  
A. Kourmatzis ◽  
J. S. Shrimpton
Keyword(s):  
Spatial Data ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Two Dimensions ◽  
Three Dimensions ◽  
Energy Budgets ◽  
Turbulent Regime ◽  
Scalar Flux ◽  
Wide Range ◽  
Scalar Variance

AbstractThe fundamental mechanisms responsible for the creation of electrohydrodynamically driven roll structures in free electroconvection between two plates are analysed with reference to traditional Rayleigh–Bénard convection (RBC). Previously available knowledge limited to two dimensions is extended to three-dimensions, and a wide range of electric Reynolds numbers is analysed, extending into a fully inherently three-dimensional turbulent regime. Results reveal that structures appearing in three-dimensional electrohydrodynamics (EHD) are similar to those observed for RBC, and while two-dimensional EHD results bear some similarities with the three-dimensional results there are distinct differences. Analysis of two-point correlations and integral length scales show that full three-dimensional electroconvection is more chaotic than in two dimensions and this is also noted by qualitatively observing the roll structures that arise for both low (${\mathit{Re}}_{E} = 1$) and high electric Reynolds numbers (up to ${\mathit{Re}}_{E} = 120$). Furthermore, calculations of mean profiles and second-order moments along with energy budgets and spectra have examined the validity of neglecting the fluctuating electric field ${ E}_{i}^{\ensuremath{\prime} } $ in the Reynolds-averaged EHD equations and provide insight into the generation and transport mechanisms of turbulent EHD. Spectral and spatial data clearly indicate how fluctuating energy is transferred from electrical to hydrodynamic forms, on moving through the domain away from the charging electrode. It is shown that ${ E}_{i}^{\ensuremath{\prime} } $ is not negligible close to the walls and terms acting as sources and sinks in the turbulent kinetic energy, turbulent scalar flux and turbulent scalar variance equations are examined. Profiles of hydrodynamic terms in the budgets resemble those in the literature for RBC; however there are terms specific to EHD that are significant, indicating that the transfer of energy in EHD is also attributed to further electrodynamic terms and a strong coupling exists between the charge flux and variance, due to the ionic drift term.

scholarly journals Focusing of Particles in a Microchannel with Laser Engraved Groove Arrays

Biosensors ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 263
Author(s):  
Tianlong Zhang ◽  
Yigang Shen ◽  
Ryota Kiya ◽  
Dian Anggraini ◽  
Tao Tang ◽  
...  
Keyword(s):  
Open Space ◽  
Lateral Displacement ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Particle Sedimentation ◽  
Nanoparticle Separation ◽  
Wide Range ◽  
Fs Laser ◽  
Channel Bottom ◽  
Myoblast Cells

Continuous microfluidic focusing of particles, both synthetic and biological, is significant for a wide range of applications in industry, biology and biomedicine. In this study, we demonstrate the focusing of particles in a microchannel embedded with glass grooves engraved by femtosecond pulse (fs) laser. Results showed that the laser-engraved microstructures were capable of directing polystyrene particles and mouse myoblast cells (C2C12) towards the center of the microchannel at low Reynolds numbers (Re < 1). Numerical simulation revealed that localized side-to-center secondary flows induced by grooves at the channel bottom play an essential role in particle lateral displacement. Additionally, the focusing performance proved to be dependent on the angle of grooves and the middle open space between the grooves based on both experiments and simulation. Particle sedimentation rate was found to critically influence the focusing of particles of different sizes. Taking advantage of the size-dependent particle lateral displacement, selective focusing of micrometer particles was demonstrated. This study systematically investigated continuous particle focusing in a groove-embedded microchannel. We expect that this device will be used for further applications, such as cell sensing and nanoparticle separation in biological and biomedical areas.

The Effect of Pulsed Blowing on the Boundary Layer of a Highly Loaded Low Pressure Turbine Blade

2013 ◽  
Author(s):  
Marion Mack ◽  
Roland Brachmanski ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Mach Number ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Trailing Edge ◽  
Low Pressure Turbine ◽  
Wide Range ◽  
Highly Loaded

The performance of the low pressure turbine (LPT) can vary appreciably, because this component operates under a wide range of Reynolds numbers. At higher Reynolds numbers, mid and aft loaded profiles have the advantage that transition of suction side boundary layer happens further downstream than at front loaded profiles, resulting in lower profile loss. At lower Reynolds numbers, aft loading of the blade can mean that if a suction side separation exists, it may remain open up to the trailing edge. This is especially the case when blade lift is increased via increased pitch to chord ratio. There is a trend in research towards exploring the effect of coupling boundary layer control with highly loaded turbine blades, in order to maximize performance over the full relevant Reynolds number range. In an earlier work, pulsed blowing with fluidic oscillators was shown to be effective in reducing the extent of the separated flow region and to significantly decrease the profile losses caused by separation over a wide range of Reynolds numbers. These experiments were carried out in the High-Speed Cascade Wind Tunnel of the German Federal Armed Forces University Munich, Germany, which allows to capture the effects of pulsed blowing at engine relevant conditions. The assumed control mechanism was the triggering of boundary layer transition by excitation of the Tollmien-Schlichting waves. The current work aims to gain further insight into the effects of pulsed blowing. It investigates the effect of a highly efficient configuration of pulsed blowing at a frequency of 9.5 kHz on the boundary layer at a Reynolds number of 70000 and exit Mach number of 0.6. The boundary layer profiles were measured at five positions between peak Mach number and the trailing edge with hot wire anemometry and pneumatic probes. Experiments were conducted with and without actuation under steady as well as periodically unsteady inflow conditions. The results show the development of the boundary layer and its interaction with incoming wakes. It is shown that pulsed blowing accelerates transition over the separation bubble and drastically reduces the boundary layer thickness.

Predictions of the Effect of Roughness on Heat Transfer From Turbine Airfoils

1998 ◽  
Author(s):  
Anil K. Tolpadi ◽  
Michael E. Crawford
Keyword(s):  
Heat Transfer ◽  
Side Surface ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Surface Finishing ◽  
Transfer Coefficients ◽  
Average Roughness ◽  
Wide Range ◽  
Turbine Airfoils ◽  
Good Agreement

The heat transfer and aerodynamic performance of turbine airfoils are greatly influenced by the gas side surface finish. In order to operate at higher efficiencies and to have reduced cooling requirements, airfoil designs require better surface finishing processes to create smoother surfaces. In this paper, three different cast airfoils were analyzed: the first airfoil was grit blasted and codep coated, the second airfoil was tumbled and aluminide coated, and the third airfoil was polished further. Each of these airfoils had different levels of roughness. The TEXSTAN boundary layer code was used to make predictions of the heat transfer along both the pressure and suction sides of all three airfoils. These predictions have been compared to corresponding heat transfer data reported earlier by Abuaf et al. (1997). The data were obtained over a wide range of Reynolds numbers simulating typical aircraft engine conditions. A three-parameter full-cone based roughness model was implemented in TEXSTAN and used for the predictions. The three parameters were the centerline average roughness, the cone height and the cone-to-cone pitch. The heat transfer coefficient predictions indicated good agreement with the data over most Reynolds numbers and for all airfoils-both pressure and suction sides. The transition location on the pressure side was well predicted for all airfoils; on the suction side, transition was well predicted at the higher Reynolds numbers but was computed to be somewhat early at the lower Reynolds numbers. Also, at lower Reynolds numbers, the heat transfer coefficients were not in very good agreement with the data on the suction side.

CFD Simulation of Fluid Flow Through Porous Media: Application to Decomposed Gases Flow Through Foam Pattern in Lost Foam Casting

Materials ◽  
2003 ◽  
Author(s):  
Sayavur I. Bakhtiyarov ◽  
Ruel A. Overfelt
Keyword(s):  
Cfd Simulation ◽  
Reynolds Numbers ◽  
Phase Flow ◽  
Flow Through Porous Media ◽  
Foam Material ◽  
Element Analysis ◽  
Wide Range ◽  
Flow Through ◽  
Foam Pattern ◽  
Lost Foam

Numerical simulation of decomposed gases through foam pattern was conducted using finite element analysis. A new kinetic model is proposed for gaseos phase flow between molten metal and foam material. The computations were performed for a wide range of Reynolds numbers. The results of the simulations are compared with the experiemental data obtained in this study.

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