scholarly journals RANS and SRS simulations of the flow around a smooth cylinder

2020 ◽  
Vol 310 ◽  
pp. 00031
Author(s):  
Ivan Kološ ◽  
Lenka Lausová ◽  
Vladimíra Michalcová
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Simulation Models ◽  
Computational Domain ◽  
3D Mesh ◽  
Smooth Cylinder ◽  
Flow Around Circular Cylinder ◽  
2D And 3D

The paper focuses on the numerical simulation of the flow around circular cylinder with Reynolds number 2∙104. The 2D and 3D mesh is used for the computational domain. RANS turbulence model SST k-ω is used for the 2D task. The 3D task is solved using Scale-Resolving Simulation models LES, SAS, DES. Drag coefficient, lift coefficient, pressure coefficient and velocity field in the wake are evaluated.

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.

Shear versus vortex-induced lift force on a rigid sphere at moderate Re

2002 ◽  
Vol 473 ◽  
pp. 379-388 ◽  
Author(s):  
P. BAGCHI ◽  
S. BALACHANDAR
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Shear Flow ◽  
Lift Force ◽  
Lift Coefficient ◽  
Rigid Sphere ◽  
Free Rotation ◽  
Rigid Spheres ◽  
Linear Shear ◽  
Strong Lift

The lift forces on rigid spheres entrained in a vortex and a linear shear flow are computed using a direct numerical simulation. The sphere Reynolds number is in the range 10 to 100. The lift coefficient in a vortex is shown to be nearly two orders of magnitude higher than that in a shear flow. The inviscid mechanism is shown to be inadequate to account for the enhanced lift force. The effect of free rotation of the sphere is also shown to be too small to account for the enhanced lift force. Flow structure around the sphere is studied to explain the generation of the strong lift force in a vortex.

Phase-Lag-Induced Fluctuating Lift Forces on Two Tandem Bluff Bodies

2015 ◽  
Author(s):  
Md. Mahbub Alam ◽  
Ma Zhe
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Vortex Dynamics ◽  
Lift Coefficient ◽  
Nonlinear Function ◽  
Local Maximum ◽  
Circular Cylinders ◽  
Bluff Bodies ◽  
Phase Lag ◽  
Spacing Ratio

A numerical simulation at a Reynolds number Re = 200 is conducted to find how flow-induced forces on two tandem circular cylinders is connected to the phase lag between vortex sheddings from the cylinders. The spacing ratio L* (= L/D) is varied from 2 to 9, where L is the cylinder center-to-center spacing and D is the cylinder diameter. Here we mainly focus on fluctuating lift coefficient CLf of the upstream cylinder, vortex dynamics in the gap between cylinders, and phase lag ϕ between the vortex sheddings from the two cylinders for L* larger than the critical where the co-shedding flow prevails. ϕ is indeed nonlinear function of L*, Strouhal number (St) and convection velocity of vortices in the gap between the cylinders. We unearth that the upstream cylinder CLf is affected by both L* and ϕ. While the contribution of L* to CLf diminishes rapidly with L*, that of ϕ makes the L*-dependent CLf variation damped-sinusoidal, persisting in the L* range examined. The inphase and antiphase flows respectively correspond to a local maximum and minimum CLf. How CLf is correlated with L* and ϕ can be deduced as, C L f = A e −α L * + B e −β L * sin ϕ + π 2 + C , where A, α, B, β and C are constants. The physics behind the damped-sinusoidal variation in CLf is discussed.

Wavelet Analysis of Reynolds Number Effect on 3-D Vorticity in a Turbulent Near Wake

2003 ◽  
Author(s):  
M. W. Yiu ◽  
H. Li ◽  
Y. Zhou
Keyword(s):  
Reynolds Number ◽  
Large Scale ◽  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Vortex Formation ◽  
Small Scale ◽  
Stream Velocity ◽  
Near Wake ◽  
Scale Structures ◽  
Three Components

When Reynolds number, Re (≡U∞d/v, where U∞ is the free stream velocity, d is the cylinder diameter and v is the kinematic viscosity of the fluid), is in the range of 103 to 104, there is a large variation in the near-wake formation region in terms of the base pressure coefficient, the fluctuating lift coefficient, the vortex formation length, which have previously been connected to the generation of small-scale Kelvin-Helmholtz vortices. This work aims to investigate how this Re variation affects the three components of vorticity in terms of time-averaged and small-scale structures and also to provide a relatively complete set of 3-D vorticity data. All three components of vorticity data were simultaneously measured in the intermediate region of the turbulent wake using a multi-wire vorticity probe. It is observed that the root-mean-square (rms) values of the three vorticity components increase with Re, especially the streamwise component, which shows a large jump from Re = 5×103 to 104. At the central frequencies of f0 and 2f0, the contributions from the large-scale and intermediate-scale structures of ωzi2/(ωz2)max decreases 13% and 16% respectively as the Re. increases. However, at the central frequency of 16f0, the contribution of the small-scale structure of ωzi2/(ωz2)max dramatic suddenly 7% increase at Re = 5×103 to 104. The result suggest the generation of small-scale Kelvin-Helmholtz vortices in the spanwise structure. The effect of Re on vorticity signals, spectra, contributions from the wavelet components to the vorticity variances are also examined.

Computational Investigation of Full-Scale Tethered Underwater Kite

2018 ◽  
Author(s):  
Amirmahdi Ghasemi ◽  
David J. Olinger ◽  
Gretar Tryggvason
Keyword(s):  
Numerical Simulation ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Simulation Models ◽  
Slip Boundary Condition ◽  
Full Scale ◽  
Grid Resolution ◽  
Ocean Current ◽  
Computational Domain ◽  
Fixed Structure

In this paper, a numerical simulation of three-dimensional motion of tether undersea kites (TUSK) for power generation is studied. TUSK systems includes a rigid-winged kite, or glider, moving in an ocean current in which a tethered kite is connected by a flexible tether to a fixed structure. Kite hydrodynamic forces are transmitted through the tether to an electrical generator on the fixed structure. The numerical simulation models the flow field in a three-dimensional domain near the rigid undersea kite wing by solving the full Navier-Stokes equations. In order to resolve the boundary layer near the kite surface, adequate grid resolution is needed which increases the computational run time drastically especially in 3D simulations. Therefore, in this study a slip boundary condition is implemented at the kite interface to accurately predict the total drag, with lower grid resolution. In order to reduce the numerical run times, a moving computational domain method is also used. A PID controller is used to adjuste the kite pitch, roll and yaw angles during power (tether reel-out) and retraction (reel-in) phases. A baseline simulation study of a full-scale TUSK system is conducted in which the expected cross-current, figure-8 motions during a kite reel-out phase is captured. The effect of the tether drag on the kite motion and resulting power output is also investigated and compared with the results of the baseline simulation.

Simulation of Tethered Underwater Kites Moving in Three Dimensions for Power Generation

2017 ◽  
Author(s):  
Amirmahdi Ghasemi ◽  
David J. Olinger ◽  
Gretar Tryggvason
Keyword(s):  
Numerical Simulation ◽  
Power Generation ◽  
Stokes Equations ◽  
Simulation Models ◽  
Three Dimensions ◽  
Ocean Current ◽  
Design Parameters ◽  
Immersed Boundary ◽  
Computational Domain ◽  
Flow Equations

In this paper, a numerical simulation of tether undersea kites (TUSK) used for power generation is undertaken. The effect of varying key design parameters in these systems is studied. TUSK systems consist of a rigid-winged kite, or glider, moving in an ocean current. One proposed TUSK concept uses a tethered kite which is connected by a flexible tether to a support structure with a generator on a surface buoy. The numerical simulation models the flow field in a three-dimensional domain near the rigid undersea kite wing by solving the full Navier-Stokes equations. A moving computational domain method is used to reduce the computational run times. A second-order corrector-predictor method, along with Open Multi-Processing (OpenMP), is employed to solve the flow equations. In order to track the rigid kite, which is a rectangular planform wing with a NACA 0021 airfoil, an immersed boundary method is used. The tension force in the elastic tether is modeled by a simple Hooke’s law, and the effect of tether damping is added. PID control methods are used to adjust the kite pitch, roll and yaw angles during power (tether reel-out) and retraction (reel-in) phases to obtain the desired kite trajectories. During the reel-out phase the kite moves in successive cross-current motions in a figure-8 pattern, the tether length increases and power is generated. During reel-in the kite motion is along the tether, and kite hydrodynamic forces are reduced so that net positive power is produced. The effects of different key design parameters in TUSK systems, such as the ratio of tether to current velocity, and tether retraction velocity, are then further studied. System power output, kite trajectories, and vorticity flow fields for the kite are also determined.

scholarly journals Study of the Drag Reduction Characteristics of Circular Cylinder with Dimpled Surface

Water ◽  
2021 ◽  
Vol 13 (2) ◽  
pp. 197
Author(s):  
Fei Yan ◽  
Haifeng Yang ◽  
Lihui Wang
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Drag Reduction ◽  
Skin Friction ◽  
Vortex Shedding ◽  
Pressure Coefficient ◽  
Reduction Rate ◽  
Skin Friction Coefficient ◽  
Pressure Drag ◽  
Smooth Cylinder

To reduce the drag of a cylinder, numerical simulations and experiments for both smooth cylinder and circular cylinder with the dimpled surface are carried out in this paper. The numerical simulation focuses on the variation of pressure coefficient, skin friction coefficient, and vortex shedding strength of the smooth cylinder and the circular cylinder with the dimpled surface. It is found that the dimpled structure can effectively reduce the drag of the cylinder within a specific range of Reynolds number, and the maximum drag reduction rate reaches up to 19%. Another conclusion is that the pressure drag and skin friction drag have an essential influence on the total drag of the circular cylinder with the dimpled surface. On the other hand, the strength of vortex shedding also decreases with the decrease of cylinder drag. Then, the flow field of both cylinders is measured using the particle image velocimetry (PIV) technique, confirming that the dimpled structure can affect the velocity field, the release of vortices and the scale of the vortex. More specifically, the velocity recovery of the circular cylinder with the dimpled surface is faster than that of the smooth cylinder, and the dimpled structure delays the release of the vortex at a specific range of Reynolds number.

scholarly journals Large Eddy Simulation of Flow over Wavy Cylinders with Different Twisted Angles at a Subcritical Reynolds Number

2019 ◽  
Vol 7 (7) ◽  
pp. 227 ◽  
Author(s):  
Chunyu Guo ◽  
Hang Guo ◽  
Jian Hu ◽  
Kewei Song ◽  
Weipeng Zhang ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Large Eddy Simulation ◽  
Vortex Structure ◽  
Pressure Coefficient ◽  
Vortex Formation ◽  
Spanwise Direction ◽  
Offshore Platforms ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Smooth Cylinder

The deformation of the cylinder has been proved to greatly reduce the fluctuation of lift and the vortex-induced vibration. In this article, a new form of deformation mode for the smooth cylinder is proposed in order to reduce the vortex-induced vibrations, which can be applied to marine risers and submarine pipelines to ensure the working performance and safety of offshore platforms. Large eddy simulation (LES) is adopted to simulate the turbulent flow over wavy cylinders with three different twisted angles at a subcritical Reynolds number Re = 28,712. Comparing with the results of smooth cylinder, the maximum drag and lift reduction of wavy cylinder A3 with α = 40° can reach 17% and 84%, respectively, and the corresponding vortex formation length increases significantly, while the turbulence intensity decreases relatively. Meanwhile, the circumferential minimum pressure coefficient is greater than that of the smooth cylinder, which also provides a greater drag reduction for the cylinder. The surface separation line, turbulent kinetic energy distribution, and wake vortex structure indicate that the elongation of separated shear layer and wake shedding position is larger than that of the smooth cylinder, and the vorticity value in the near wake region decreases. A periodic vortex structure is generated along the spanwise direction, and a weaker and more stable Karman vortex street is reformed at a further downstream position, which ultimately leads to the reduction of drag and fluctuating lift of the wavy cylinder.

scholarly journals The concept of roughness in fluvial hydraulics and its formulation in 1D, 2D and 3D numerical simulation models

2008 ◽  
Vol 46 (2) ◽  
pp. 191-208 ◽  
Author(s):  
Hervé Morvan ◽  
Donald Knight ◽  
Nigel Wright ◽  
Xiaonan Tang ◽  
Amanda Crossley
Keyword(s):  
Numerical Simulation ◽  
Simulation Models ◽  
3D Numerical Simulation ◽  
Fluvial Hydraulics ◽  
2D And 3D

scholarly journals The effects of the axis ratio on the flow and heat transfer characteristics around a drop-shaped tube

2021 ◽  
Vol 2057 (1) ◽  
pp. 012001
Author(s):  
R Deeb ◽  
D V Sidenkov
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Coefficient ◽  
Maximum Velocity ◽  
Computational Domain ◽  
Heat Transfer Characteristics ◽  
Axis Ratio ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Shaped Tube

Abstract Flow and heat transfer characteristics around single drop-shaped tubes with different axis ratio (L/D) in cross-flow are studied numerically for values of Reynolds number in the range 1.3×103 to 20×103. The results are obtained using the commercial software ANSYS Fluent for a two-dimensional (2D) computational domain. The axis ratio of the studied tubes is varied from 1 to 4, when L/D =1, the tube is circular. The simulation results agree well with the available literature. The distribution of local coefficients of pressure and friction over half of the tube’s surface is plotted and analysed. It found that the drop-shaped tubes delay the separation of the boundary layer from the tube wall. The results confirm that the minimum value of pressure coefficient decreases as L/D decreases, and the maximum value of the friction coefficient gradually increases with the growth of L/D. The result of the numerical simulation indicates the superior overall performance of drop-shaped tube with L/D=4 over the rest of the tubes. Correlations of the average Nusselt number and the friction factor in terms of Reynolds number, calculated by the maximum velocity in the minimum free cross-section, and axis ratios for the studied cases are proposed.

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