Verification Issues Related to CFD Simulations of Flow Around Circular Cylinders

2013 ◽  
Author(s):  
Jose Escobar ◽  
Ismail Celik ◽  
Albio Gutierrez-Amador
Keyword(s):  
Drag Coefficient ◽  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Classical Problem ◽  
Circular Cylinders ◽  
Estimation Methods ◽  
Cylinder Wall ◽  
Two Dimensional ◽  
Cfd Simulations ◽  
Fine Mesh

The classical problem of flow around a stationary smooth circular cylinder is used to evaluate Computational Fluid Dynamics (CFD) transient simulations using two approaches; Body Fitted Grid (BFG) and Immersed Boundary Method (IBM). BFG simulations were performed using a commercial CFD code ANSYS-FLUENT and IBM simulations using an in-house CFD code DREAM. Two dimensional simulations were performed at three different Reynolds numbers; 1 × 103, 1 × 105, and 5 × 105. Each of the cases was simulated using a coarse, medium and fine mesh. CFD simulations were evaluated using the following quantities; drag coefficient, lift coefficient, pressure coefficient, separation angle and the Strouhal number of the first harmonic of the lift coefficient. Average, and amplitude of the evaluation quantities are reported for every case. Simulations showed the grid dependence of the results, e.g. finer meshes captured higher harmonics of the drag coefficient which coarse meshes smeared due the large numerical viscosity. IBM simulations were also affected by the symmetry of the computational grid. Predicted quantities follow previously reported experimental trends fairly well except in the critical flow regime. Two dimensional calculations using turbulence models were performed for the case of Re = 1 × 105, and Re = 5 × 105. Turbulent results showed the importance of the grid resolution near the cylinder wall in capturing the physics of the problem. Three dimensional calculations were also performed and results are compared to those obtained from the two dimensional simulations. As may be expected, discretization error estimation methods using three grid calculations are not satisfactory for this highly unsteady flow problem, especially near the critical regime, 1 × 105 < Re < 5 × 105. This paper dwells on various issues related to verification of calculations for such highly unsteady flows.

scholarly journals A Study of Drag Reduction on Cylinders with Different V-Groove Depths on the Surface

Water ◽  
2021 ◽  
Vol 14 (1) ◽  
pp. 36
Author(s):  
Jiyang Qi ◽  
Yue Qi ◽  
Qunyan Chen ◽  
Fei Yan
Keyword(s):  
Drag Reduction ◽  
Drag Coefficient ◽  
Vortex Structure ◽  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Reynolds Numbers ◽  
Groove Surface ◽  
Smooth Cylinder ◽  
Groove Structure ◽  
Reduction Effect

In this study, the drag reduction effect is studied for a cylinder with different V-groove depths on its surface using a k-ω/SST (Shear Stress Transport) turbulence model of computational fluid dynamics (CFD), while a particle image velocimetry (PIV) system is employed to analyze the wake characteristics for a smooth cylinder and a cylinder with different V-groove depths on its surface at different Reynolds numbers. The study focuses on the characteristics of the different V-groove depths on lift coefficient, drag coefficient, the velocity distribution of flow field, pressure coefficient, vortex shedding, and vortex structure. In comparison with a smooth cylinder, the lift coefficient and drag coefficient can be reduced for a cylinder with different V-groove depths on its surface, and the maximum reduction rates of lift coefficient and drag coefficient are about 34.4% and 16%, respectively. Otherwise, the vortex structure presents a complete symmetry for the smooth cylinder, however, the symmetry of the vortex structure becomes insignificant for the V-shaped groove structure with different depths. This is also an important reason for the drag reduction effect of a cylinder with a V-groove surface.

scholarly journals Numerical Analysis of Fluid Flow on Wall Cylinder Circular with K-ε Modeling for a High Reynolds Rate

2019 ◽  
Vol 1 (3) ◽  
pp. 43-50
Author(s):  
M. Yasep Setiawan ◽  
Wawan Purwanto ◽  
Wanda Afnison ◽  
Nuzul Hidayat
Keyword(s):  
Fluid Flow ◽  
Numerical Study ◽  
General Procedure ◽  
Circular Cylinders ◽  
Cylinder Wall ◽  
Two Dimensional ◽  
Third Order ◽  
Physical Information ◽  
Flow Through ◽  
High Reynolds

This study discusses the numerical study of two-dimensional analysis of flow through circular cylinders. The original physical information entered in the equation governing most of the modeling is transferred into a numerical solution. Fluid flow on two-dimensional circular cylinder wall using high Reynolds k-ε modeling (Re = 106), Here we will do 3 modeling first oder upwind, second order upwind and third order MUSCL by using k-ε standard.  The general procedure for this research is formulated in detail for allocations in the dynamic analysis of fluid computing. The results of this study suggest that MUSCL's third order modeling gives more accurate results better than other models.

scholarly journals The effect of compressibility on the lift of an aerofoil

1928 ◽  
Vol 118 (779) ◽  
pp. 113-119 ◽  
Keyword(s):  
Drag Coefficient ◽  
High Speed ◽  
Lift Coefficient ◽  
Experimental Investigations ◽  
Angle Of Incidence ◽  
Two Dimensional ◽  
Velocity Of Sound ◽  
Similar Calculation ◽  
Incompressible Medium ◽  
Observed Behaviour

At ordinary aeroplane speeds the effect of the compressibility of the air is very small, and there is complete justification for the usual assumption that the air may be regarded effectively as an incompressible medium. This assumption, however, ceases to be valid in the case of high tip-speed airscrews and is not really satisfactory even when the tip speed is no greater than 800 f. p. s. It is important, therefore, to examine, both theoretically and experimentally, the effect of compressibility at high speed on the characteristics of an aerofoil. Experimental investigations are in progress at the Royal Aircraft Establishment in which the aerofoil characteristics are derived by analysing the observed behaviour of high-speed model airscrews, but owing to the complexity both of the experiments and of the analysis it is impossible that the results should have the same accuracy as those obtained from direct tests of an aerofoil at low speed. An attempt has now been made to estimate theoretically the effect of compressibility on the lift of an aerofoil in two-dimensional motion and to indicate the nature of the variation which may be anticipated in the curve of lift coefficient against angle of incidence. It is unfortunately impossible at the present state of knowledge to make any similar calculation for the drag of the aerofoil, but on general grounds we may anticipate that the drag coefficient will rise at an increasing rate until the velocity of sound is reached, and that above this speed the drag coefficient will decrease again, remaining, however, higher than at low speeds.

Wakes of Developed Cavities

1977 ◽  
Vol 21 (04) ◽  
pp. 225-238
Author(s):  
Jean-Marie Michel
Keyword(s):  
Free Surface ◽  
Boundary Conditions ◽  
Drag Coefficient ◽  
Cavity Length ◽  
Lift Coefficient ◽  
Cavity Flow ◽  
Numerical Results ◽  
Two Dimensional ◽  
Flow Configuration ◽  
Wake Model

A linearized wake model with a momentum defect is presented for the two-dimensional cavity flow around a base-vented foil which is placed in a free-surface channel. The numerical results show that, for a given cavity underpressureσ, the boundary conditions on the wake of the cavity have repercussions on the cavity length and the lift coefficient, whereas the drag coefficient is not modified. Similar features can be expected whenever the flow configuration is made strongly asymmetric by the external boundaries, especially by a free surface.

scholarly journals Research on Compressible Flow around Cylinder and Truncated Cone with LES Method

2014 ◽  
Vol 919-921 ◽  
pp. 210-215
Author(s):  
Meng Zhao ◽  
Jun Mao ◽  
Guo Wei Yang
Keyword(s):  
Drag Coefficient ◽  
Compressible Flow ◽  
Bluff Body ◽  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Scale Model ◽  
Windward Side ◽  
Leeward Side ◽  
Filter Function ◽  
Truncated Cone

Numerical simulation with the large eddy simulation, filter function, and Smagorinsky sub-grid scale model is adopted to simulate the compressible flow around a bluff body finite length circular cylinder and truncated cone in high Reynolds number. The law of the drag coefficient, lift coefficient and pressure coefficient obtained from models with various cross-wind speeds was discussed. Process of the vortex generated, shed and dissipated was analyzed and the relationship between the press filed, velocity filed and vortex filed was also analyzed. Average value of the drag coefficient, lift coefficient and pressure coefficient of the circle cylinder in subcritical region are greater than truncated cone. Values of pressure coefficient on the windward side of all the models are consistent. However, it various widely on the leeward side, even on the end face of the cone and cylinder.

The predominant frequency for viscous flow past two tandem circular cylinders of different diameters at low Reynolds number

2019 ◽  
Vol 234 (2) ◽  
pp. 534-546
Author(s):  
Ming-ming Liu
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
Viscous Flow ◽  
Lift Coefficient ◽  
Circular Cylinders ◽  
Predominant Frequency ◽  
Flow Past ◽  
Gap Ratio ◽  
The Mean ◽  
Different Diameters

Viscous flow past two circular cylinders in tandem arrangement is numerically investigated at a typical Reynolds number of 200 which is based on the diameter of the downstream cylinder. The non-dimensional diameter of the downstream cylinder D is fixed to be 1.0, while the non-dimensional diameter of the upstream cylinder d varies from 0.1 to 1.0 with an interval of 0.1. Moreover, the minimal non-dimensional distance between the two cylinders changes from 0.1 to 4.0. The numerical results show that continuous variation of the mean drag coefficient, the lift coefficient, and the lift frequency is observed with the increase in the gap ratio for d/ D = 0.1 and 0.2. Discontinuities are found for the mean drag coefficient, the lift coefficient, and the lift frequency of the downstream cylinder with the increase in gap ratio for d/ D = 0.9 and 1.0. Multiple lift oscillating frequencies of the downstream cylinder can be detected for d/ D = 0.3–0.8 at special gap ratios. Special attention is paid on d/ D = 0.4, which is a typical example for d/ D = 0.3–0.8. The predominant lift frequency of the downstream cylinder is observed to change from fL-1 to fL-2 as the increase in the gap ratio for d/ D = 0.4, which have not been previously detected. However, the predominant drag frequency of the downstream cylinder is found always to be fD-3 in present investigation scope. Moreover, a conclusion that fD-3 =  fL-1 +  fL-2 can be obtained.

The Influence of Rotating Wheels on Vehicle Aerodynamics

2012 ◽  
Vol 246-247 ◽  
pp. 543-547 ◽  
Author(s):  
Ting Li ◽  
Qing Jia ◽  
Zhi Gang Yang
Keyword(s):  
Drag Coefficient ◽  
Lift Coefficient ◽  
Computational Simulation ◽  
Pressure Coefficient ◽  
Flow Characteristics ◽  
Aerodynamic Performance ◽  
Navier Stokes ◽  
Global Flow ◽  
Flow Surface ◽  
Vehicle Aerodynamics

Full scaled simplified model and production vehicle were applied to make a research on the local and global flow characteristics. Two different conditions including stationary and rotation were employed in computational simulation by steady RNS Navier-Stokes calculation. Further, detailed analysis on flow, surface pressure coefficient, drag coefficient and lift coefficient affected by rotating wheel figure out that rotating wheel has a significant influence on the flow around wheel and vehicle. Pressure difference, drag coefficient and lift coefficient are decreased by rotation, which improve aerodynamic performance.

Dynamic Behavior of a Streamwise Oscillating Heated Cylinder

2021 ◽  
Author(s):  
Ussama Ali ◽  
MD Islam ◽  
Isam Janajreh
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Drag Coefficient ◽  
Natural Frequency ◽  
Strouhal Number ◽  
Frequency Ratio ◽  
Lift Coefficient ◽  
Cylinder Wall ◽  
Forcing Function ◽  
Lower Amplitude

Abstract The influence of oscillation and heat transfer on the lift and drag coefficients over a circular cylinder is numerically studied in this work. Temperature difference of 300, 600 and 900 K is used between the cylinder wall and the incoming fluid flow for Reynolds number of 100. Air is used as the fluid and the temperature dependent properties of air are used for the analysis as a significant change in the properties of air incurred. Numerical simulation is done on Ansys/fluent with O-type mesh and the vibration in the circular cylinder is induced using user defined function. The vibration of the cylinder in streamwise direction is induced at a frequency ratio of 0.5, 1, and 2, with the natural frequency of the cylinder being 2.5 Hz marking its Strouhal number. It is observed that for all the induced frequencies, the forcing function interacts with the natural frequency of the system, and the beating phenomenon spectrum is observed, where two distinct frequencies appear which correspond to the sum and difference between the natural and the forcing frequency. At the frequency ratio of 0.5 (1.25 Hz), the spectrum of lift coefficient is characterized with three peaks centered at 2.5 Hz (natural frequency), 3.75 Hz (sum) and 1.25 Hz (difference). Oscillating the isothermal cylinder at a frequency ratio of 0.5 caused a negligible increase in the rms value of the lift coefficient by 2.13%, drag coefficient by 0.17%, and had no effect on the natural frequency of the system, however at a frequency ratio of 2, a drastic increase in the rms value of lift coefficient by 137.4% and drag coefficient by 13.9% occurred, indicating the lock-on regime. As compared to the stationary isothermal cylinder, heating the cylinder 300K above the incoming flow, decreased the rms value of the lift coefficient by 62.7% and the natural frequency by 16%, while increased the drag coefficient by 7.3%. The results show that heating of cylinder in cross-flow is equivalent to running the flow at a reduced Reynolds number and in the laminar region, this is associated with lower Strouhal number and lower amplitude of lift but a higher drag.

Numerical simulation of flow past two circular cylinders in cruciform arrangement

2018 ◽  
Vol 848 ◽  
pp. 1013-1039 ◽  
Author(s):  
Ming Zhao ◽  
Lin Lu
Keyword(s):  
Standard Deviation ◽  
Drag Coefficient ◽  
Flow Pattern ◽  
Vortex Shedding ◽  
Lift Coefficient ◽  
Circular Cylinders ◽  
Local Flow ◽  
Wake Vortices ◽  
Flow Past ◽  
The Mean

Flow past two circular cylinders in cruciform arrangement is simulated by direct numerical simulations for Reynolds numbers ranging from 100 to 500. The study is aimed at investigating the local flow pattern near the gap between the two cylinders, the global vortex shedding flow in the wake of the cylinders and their effects on the force coefficients of the two cylinders. The three identified local flow patterns near the gap: trail vortex (TV), necklace vortex (NV) and vortex shedding in the gap (SG) agree with those found by flow visualization in experimental studies. As for the global wake flow, two modes of vortex shedding are identified: K mode with inclined wake vortices and P mode where the wake vortices are parallel to the cylinders. The K mode occurs when the gap is slightly greater than the boundary gap between the NV and SG. It also coexists with the SG gap flow pattern if the Reynolds number is very small ($Re=100$). The flow pattern affects the force coefficient. The K mode increases the mean drag coefficient and the standard deviation of the lift coefficient at the centre of the upstream cylinder because the wake vortices converge towards the centre. The mean drag coefficient and standard deviation of the lift coefficient of the downstream cylinder decreases because of the shedding effect from the upstream cylinder.

Effects of Masts on the Aerodynamics of Sail Sections

1978 ◽  
Vol 15 (01) ◽  
pp. 35-42
Author(s):  
Jerome H. Milgram
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
Lift Coefficient ◽  
Limited Range ◽  
Cross Sectional Area ◽  
Water Tunnel ◽  
Two Dimensional ◽  
Sectional Area ◽  
Cross Sectional ◽  
Coefficient Versus

The effects of the addition of masts of varying geometries to two different sail-like two-dimensional airfoil sections were determined by water tunnel tests. Thirteen different mast-sail combinations were tested with four of the sections retested at a different time to confirm repeatability of the data. The results were found to be best presented and best understood by means of graphs of drag coefficient versus lift coefficient for fixed values of d/c(mast diameter/sail chord). The additional drag caused by the addition of a mast was found to be substantial, especially as the ratio d/cbecame relatively large. Results were found to be insensitive to changes in Reynolds number of a factor of two for d/cless than 0.3 for round masts, and 0.2 for elliptical masts (d for an elliptical mast is taken as the diameter of a circle having the same cross-sectional area). Elliptical masts with d/c greater than 0.3 gave results which exhibited a sensitivity to Reynolds number and which, over a limited range of lift coefficients, gave an unexpectedly high value of the ratio of lift coefficient/drag coefficient.

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