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.

Large eddy simulation of flow over a twisted cylinder at a subcritical Reynolds number

2014 ◽  
Vol 759 ◽  
pp. 579-611 ◽  
Author(s):  
Jae Hwan Jung ◽  
Hyun Sik Yoon
Keyword(s):  
Reynolds Number ◽  
Large Eddy Simulation ◽  
Shear Layer ◽  
Vortex Shedding ◽  
Vortex Formation ◽  
The Body ◽  
Recirculation Region ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Drag And Lift

AbstractWe consider a twisted cylinder that was designed by rotating the elliptic cross-section along the spanwise direction, resulting in a passive control. The flow over the twisted cylinder is investigated at a subcritical Reynolds number (Re) of 3000 using large eddy simulation based on the finite volume method. For comparison, the flow past smooth and wavy cylinders is also calculated. The twisted cylinder achieves reductions of approximately 13 and 5 % in mean drag compared with smooth and wavy cylinders, respectively. In particular, the root mean square (r.m.s.) value of the lift fluctuation of the twisted cylinder shows a substantial decrease of approximately 96 % compared with the smooth cylinder. The shear layer of the twisted cylinder covering the recirculation region is more elongated than those of the smooth and wavy cylinders, and vortex shedding from the twisted cylinder is considerably suppressed. Consequently, the elongation of the shear layer from the body and the near disappearance of vortex shedding in the near wake with weak vortical strength contributes directly to the reduction of drag and lift oscillation. Various fundamental mechanisms that affect the flow phenomena, three-dimensional separation, pressure coefficient, vortex formation length and turbulent kinetic energy are examined systematically to demonstrate the effect of the twisted cylinder surface. In addition, for the twisted cylinder at $\mathit{Re}=3000$, the effect of the cross-sectional aspect ratio is investigated from 1.25 to 2.25 to find an optimal value that can reduce the drag and lift forces. Moreover, the effect of the Reynolds number on the aerodynamic characteristics is investigated in the range of $3\times 10^{3}\leqslant \mathit{Re}\leqslant 1\times 10^{4}$. We find that as Re increases, the mean drag and the r.m.s. lift coefficient of the twisted cylinder increase, and the vortex formation length decreases.

Numerical investigation of flow around cylinder at Reynolds number = 3900 with large eddy simulation technique: Effect of spanwise length and mesh resolution

2018 ◽  
Vol 233 (2) ◽  
pp. 417-427 ◽  
Author(s):  
Niaz Bahadur Khan ◽  
Zainah Ibrahim ◽  
Ahmad Badarudin Bin Mohamad Badry ◽  
Mohammed Jameel ◽  
Muhammad Faisal Javed
Keyword(s):  
Reynolds Number ◽  
Large Eddy Simulation ◽  
Near Field ◽  
Spanwise Direction ◽  
Wake Region ◽  
Eddy Simulation ◽  
Flow Around Cylinder ◽  
Large Eddy ◽  
Mesh Resolution ◽  
Recirculation Length

Flow around a cylinder at a Reynolds number of 3900 was studied using large eddy simulation with ICEM CFD and Fluent tools for meshing and analysis, respectively. Although this issue has been explored by numerous researchers, a discrepancy still exists in the results, particularly in calculating the angle of separation, recirculation length, and statistics in the wake region behind the cylinder. In addition, the effect of spanwise grid and near-field grid resolution on the wake region needs to be addressed. This study reviews previous work and performs analyses according to the literature recommendations. The effect of spanwise length (4D, 8D, and 16D), mesh resolution in the spanwise direction (1, 10, 20, 40, 60, 80, and 160 elements), and near-field grid on calculating recirculation length, angle of separation, and wake characteristics is investigated. Hydrodynamic values and pressure distribution around the cylinder are analyzed. The wake behind the cylinder is investigated within 10 diameters. This study concluded that compared with spanwise length, mesh resolution in the spanwise direction and near-field grid are more important factors for good-quality results.

Large eddy simulation study of turbulent flow around smooth and rough domes

2013 ◽  
Vol 227 (12) ◽  
pp. 2686-2700 ◽  
Author(s):  
N Kharoua ◽  
L Khezzar
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flow ◽  
Flow Behavior ◽  
Pressure Coefficient ◽  
Horseshoe Vortex ◽  
Scale Model ◽  
Stream Velocity ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Large Eddy

Large eddy simulation of turbulent flow around smooth and rough hemispherical domes was conducted. The roughness of the rough dome was generated by a special approach using quadrilateral solid blocks placed alternately on the dome surface. It was shown that this approach is capable of generating the roughness effect with a relative success. The subgrid-scale model based on the transport of the subgrid turbulent kinetic energy was used to account for the small scales effect not resolved by large eddy simulation. The turbulent flow was simulated at a subcritical Reynolds number based on the approach free stream velocity, air properties, and dome diameter of 1.4 × 105. Profiles of mean pressure coefficient, mean velocity, and its root mean square were predicted with good accuracy. The comparison between the two domes showed different flow behavior around them. A flattened horseshoe vortex was observed to develop around the rough dome at larger distance compared with the smooth dome. The separation phenomenon occurs before the apex of the rough dome while for the smooth dome it is shifted forward. The turbulence-affected region in the wake was larger for the rough dome.

Large Eddy Simulation of the Flow Around a Diffuser-Equipped Bluff Body in Ground Effect

2011 ◽  
Author(s):  
Lara Schembri Puglisevich ◽  
Gary Page
Keyword(s):  
Large Eddy Simulation ◽  
Bluff Body ◽  
Vortex Formation ◽  
Ground Effect ◽  
Vortical Flow ◽  
Navier Stokes ◽  
Flow Structures ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Features

Unsteady Large Eddy Simulation (LES) is carried out for the flow around a bluff body equipped with an underbody rear diffuser in close proximity to the ground, representing an automotive diffuser. The goal is to demonstrate the ability of LES to model underbody vortical flow features at experimental Reynolds numbers (1.01 × 106 based on model height and incoming velocity). The scope of the time-dependent simulations is not to improve on Reynolds-Averaged Navier Stokes (RANS), but to give further insight into vortex formation and progression, allowing better understanding of the flow, hence allowing more control. Vortical flow structures in the diffuser region, along the sides and top surface of the bluff body are successfully modelled. Differences between instantaneous and time-averaged flow structures are presented and explained. Comparisons to pressure measurements from wind tunnel experiments on an identical bluff body model shows a good level of agreement.

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