scholarly journals Numerical Simulation of Flow Control around a Circular Cylinder by Installing a Wedge-Shaped Device Upstream

2019 ◽  
Vol 7 (12) ◽  
pp. 422 ◽  
Author(s):  
Xiaoshuang Han ◽  
Jie Wang ◽  
Bo Zhou ◽  
Guiyong Zhang ◽  
Soon-Keat Tan
Keyword(s):  
Circular Cylinder ◽  
Cavity Mode ◽  
Wake Flow ◽  
Side Length ◽  
Length Ratio ◽  
Drag And Lift Coefficients ◽  
Spacing Ratio ◽  
Wake Patterns ◽  
Drag And Lift ◽  
Sudden Jump

The effect of a triangular wedge upstream of a circular cylinder has been investigated, and the findings are presented herein. The triangular wedge is equilateral in plan form, and the Reynolds number based on the diameter of the main cylinder is approximately 200. Contours of vorticity clearly show that two entirely different wake patterns exist between the wedge and the main cylinder. There also exists a critical spacing ratio and side length ratio at which the wake flow pattern shifts from one within the cavity mode to one within the wake impingement mode. For a relatively small side length ratio of l w / D = 0.20 and 0.27, where the side length refers to the length of one side of the triangular wedge, the drag and lift coefficients decrease monotonically with the spacing ratio. There is a sudden jump of the drag and lift coefficients at larger side length ratios of l w / D = 0.33 and 0.40. This study shows that at a spacing ratio of L/D = 2.8 (where L is the distance between the vertex of the wedge and the center of the cylinder) and a wedge side length of l w / D = 0.40, the reduction of the amplitude of lift and mean drag coefficient on the main cylinder are 71.9% and 60.1%, respectively.

Numerical Simulation of Cross-Flow around Four Square Cylinders in a Square Configuration at Low Reynolds Number

2013 ◽  
Vol 423-426 ◽  
pp. 1700-1704
Author(s):  
Wei Zhang ◽  
Wen Jie Li ◽  
Hui Hua Ye ◽  
Dian Xin Zhang
Keyword(s):  
Cross Flow ◽  
Reynold Number ◽  
Drag And Lift Coefficients ◽  
Square Cylinders ◽  
Spacing Ratio ◽  
Low Reynolds ◽  
Four Square ◽  
Drag And Lift ◽  
Square Configuration ◽  
Volume Method

A two-dimensional finite volume method with unstructured mesh is used to simulate the flow around four square cylinders in a square configuration at low Reynolds numbers.The vorticity field, drag and lift coefficients, and Strouhal number are resolved at different spacing ratios. The vortex-shedding process and fluid-structure interactions of four square cylinders are analyzed at Reynold number of 100. The results show that the spacing ratio has important effect on the drag and lift coefficients. The accuracy of the numerical scheme are validated against other numerical and experimental data.

Interaction of a Steady Approach Flow and a Circular Cylinder Undergoing Forced Oscillation

1997 ◽  
Vol 119 (4) ◽  
pp. 808-813 ◽  
Author(s):  
Jianfeng Zhang ◽  
Charles Dalton
Keyword(s):  
Circular Cylinder ◽  
Vortex Shedding ◽  
Stokes Equations ◽  
Numerical Study ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Large Eddy Simulation Model ◽  
Drag And Lift Coefficients ◽  
Eddy Simulation ◽  
Drag And Lift

This paper presents a numerical study on the interaction of a steady approach flow and the forced transverse oscillation of a circular cylinder. The two-dimensional stream-function/vorticity formulation of the Navier-Stokes equations is solved by a semi-implicit finite-difference scheme. Calculations for flows with different amplitude (a) and frequency (fc) of the oscillation of the cylinder show a strong effect of the oscillation when fc is close to fso, the vortex shedding frequency, of the stationary cylinder. Lock-on of vortex shedding, distinct flow patterns, and increase in both drag and lift coefficients from those of a stationary cylinder are observed for Reynolds number Re = 200, a/R (R is the radius of the cylinder) from 1.0 to 2.0, fc/fso from 0.85 to 1.7. For Re = 855, a/R = 0.26, a large eddy simulation model for turbulent flow is used. The results at Re = 855 and a/R = 0.26 show that lock-on has occurred for fc/fso ≥ 0.85. The behavior of the drag and lift coefficients is seen to be influenced by the lock-on phenomenon.

scholarly journals Numerical Computations for Flow Patterns and Force Statistics of Three Rectangular Cylinders

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Hamid Rahman ◽  
Shams-ul-Islam ◽  
Waqas Sarwar Abbasi ◽  
Raheela Manzoor ◽  
Fazle Amin ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Vortex Shedding ◽  
Lift Coefficient ◽  
Flow Characteristics ◽  
Drag And Lift Coefficients ◽  
Aspect Ratios ◽  
Spacing Ratio ◽  
Drag And Lift ◽  
Rectangular Cylinders

In this work, numerical simulations are performed in order to study the effects of aspect ratio (AR) and Reynolds number (Re) on flow characteristics of three side-by-side rectangular cylinders for fixed spacing ratio ( g ), using the lattice Boltzmann method (LBM). The Reynolds number varies within the range 60 ≤ Re ≤ 180, aspect ratio is between 0.25 and 4, and spacing ratio is fixed at g  = 1.5. The flow structure mechanism behind the cylinders is analyzed in terms of vorticity contour visualization, time-trace analysis of drag and lift coefficients, power spectrum analysis of lift coefficient and variations of mean drag coefficient, and Strouhal number. For different combinations of AR and Re, the flow is characterized into regular, irregular, and symmetric vortex shedding. In regular and symmetric vortex shedding the drag and lift coefficients vary smoothly while reverse trend occurs in irregular vortex shedding. At small AR, each cylinder experiences higher magnitude drag force as compared to intermediate and large aspect ratios. The vortex shedding frequency was found to be smaller at smaller AR and increased with increment in AR.

scholarly journals Control of vortex shedding around a circular cylinder using bubble tabs in the laminar flow regime

2021 ◽  
Vol 39 (4) ◽  
pp. 1108-1116
Author(s):  
E.O. Atofarati ◽  
A.O. Muritala ◽  
B.O. Malomo ◽  
S.A. Adio
Keyword(s):  
Circular Cylinder ◽  
Drag Coefficient ◽  
Vortex Shedding ◽  
Flow Analysis ◽  
Small Diameter ◽  
Ansys Fluent ◽  
Spacing Ratio ◽  
Flow Domain ◽  
Drag And Lift ◽  
Fatigue Failures

Vortex induced vibration (VIV) is the major cause of several catastrophic disasters due to fatigue failures induced by drag and lift forces in aerodynamic systems. This study investigates the control of VIV phenomenon through passive bubble tab(s) having a small diameter (d) relative to the main circular cylinder (D) in a two-dimensional (2-D) flow domain. Using ANSYS Fluent computational software, flow analysis was conducted at a Reynolds number (Re) of 80 for various bubble tab configurations at different spacing ratios (x/D) and diameter ratios (d/D). The drag coefficient, the velocity and pressure contours, along with the flow streamlines in eachcase were studied. The results indicated the optimized tab(s) positions for different spacing ratios, diameter ratios, and  configurations. The study effectively established that passive bubble tabs can potentially control VIV associated with flows around a circular cylinder. Keywords: Vortex Shedding; Drag Coefficient; Circular Cylinder; Bubble Tab(S); Spacing Ratio; Diameter Ratio.

Numerical investigation of the vibration effect of a flexible membrane on the flow behaviour around a circular cylinder

2018 ◽  
Vol 81 (2) ◽  
pp. 21101
Author(s):  
Nabaouia Maktouf ◽  
Ali Ben Moussa ◽  
Saïd Turki
Keyword(s):  
Circular Cylinder ◽  
Strouhal Number ◽  
Bluff Body ◽  
Numerical Study ◽  
Rear Side ◽  
Ansys Fluent ◽  
Flexible Membrane ◽  
Drag And Lift Coefficients ◽  
Vibration Effect ◽  
Drag And Lift

Active control of the flow behind a bluff body is obtained by integrating a vibrating membrane. A numerical study has been conducted to investigate the effect of the vibration of a flexible membrane, stuck to the rear side of a circular cylinder, on the global flow parameters such as the Strouhal number, the drag and lift coefficients. The shape of the membrane is evolving as a vibrating chord using a dynamic mesh. The governing equations of 2D and laminar flow have been solved using ANSYS Fluent 16.0 as a solver and the Gambit as a modeler. The motion of the membrane is managed by two parameters: frequency f and amplitude A. The effect of the flexible membrane motion is studied for the range of conditions as 0.1 Hz ≤ f ≤ 6 Hz and 5 × 10−4 m ≤ A ≤ 10−3 m at a fixed Reynolds number, Re = 150. Three different sizes of the flexible membrane have been studied. Results show that a beat phenomenon affects the drag coefficient. The amplitude does not affect significantly the Strouhal number as well as drag and lift coefficients. By increasing the size of the flexible membrane, we show a lift enhancement by a growth rate equal to 39.15% comparing to the uncontrolled case.

Wake Flow of Single and Multiple Yawed Cylinders

2004 ◽  
Vol 126 (5) ◽  
pp. 861-870 ◽  
Author(s):  
A. Thakur ◽  
X. Liu ◽  
J. S. Marshall
Keyword(s):  
Computational Study ◽  
Three Dimensional ◽  
Side Wall ◽  
Wake Flow ◽  
Upstream Region ◽  
Two Dimensional ◽  
Cylinder Wake ◽  
Dimensional Approximation ◽  
The Face ◽  
Drag And Lift

An experimental and computational study is performed of the wake flow behind a single yawed cylinder and a pair of parallel yawed cylinders placed in tandem. The experiments are performed for a yawed cylinder and a pair of yawed cylinders towed in a tank. Laser-induced fluorescence is used for flow visualization and particle-image velocimetry is used for quantitative velocity and vorticity measurement. Computations are performed using a second-order accurate block-structured finite-volume method with periodic boundary conditions along the cylinder axis. Results are applied to assess the applicability of a quasi-two-dimensional approximation, which assumes that the flow field is the same for any slice of the flow over the cylinder cross section. For a single cylinder, it is found that the cylinder wake vortices approach a quasi-two-dimensional state away from the cylinder upstream end for all cases examined (in which the cylinder yaw angle covers the range 0⩽ϕ⩽60°). Within the upstream region, the vortex orientation is found to be influenced by the tank side-wall boundary condition relative to the cylinder. For the case of two parallel yawed cylinders, vortices shed from the upstream cylinder are found to remain nearly quasi-two-dimensional as they are advected back and reach within about a cylinder diameter from the face of the downstream cylinder. As the vortices advect closer to the cylinder, the vortex cores become highly deformed and wrap around the downstream cylinder face. Three-dimensional perturbations of the upstream vortices are amplified as the vortices impact upon the downstream cylinder, such that during the final stages of vortex impact the quasi-two-dimensional nature of the flow breaks down and the vorticity field for the impacting vortices acquire significant three-dimensional perturbations. Quasi-two-dimensional and fully three-dimensional computational results are compared to assess the accuracy of the quasi-two-dimensional approximation in prediction of drag and lift coefficients of the cylinders.

Simplified Aerodynamic Loading Model for Non-Production Conditions for Floating Wind Systems Design

2021 ◽  
Author(s):  
Armando Alexandre ◽  
Raffaello Antonutti ◽  
Theo Gentils ◽  
Laurent Mutricy ◽  
Pierre Weyne
Keyword(s):  
Wind Speed ◽  
Coupled Model ◽  
Systems Design ◽  
Simplified Model ◽  
Aerodynamic Loads ◽  
Drag And Lift Coefficients ◽  
Aerodynamic Loading ◽  
Yaw Bearing ◽  
Drag And Lift ◽  
Turbine Model

Abstract Floating wind is now entering a commercial-stage, and there are a significant number of commercial projects in countries like France, Japan, UK and Portugal. A floating wind project is complex and has many interdependencies and interfaces. During all stages of the project several participants are expected to use a numerical model of the whole system and not only the part the participant has to design. Examples of this are the mooring and floater designer requiring a coupled model of the whole system including also the wind turbine, the operations team requiring a model of the system to plan towing and operations. All these stakeholders require a coupled model where the hydrodynamics, aerodynamics and structural physics of the system are captured with different levels of accuracy. In this paper, we will concentrate on a simplified model for the aerodynamic loading of the turbine in idling and standstill conditions that can be easily implemented in a simulation tool used for floater, mooring and marine operations studies. The method consists of using a subset of simulations at constant wind speed (ideally close to the wind speed required for the simulations) run on a detailed turbine model on a rigid tower and fixed foundation — normally run by the turbine designer. A proxy to the aerodynamic loads on the rotor and nacelle (RNA) is to take the horizontal yaw bearing loads. The process is then repeated for a range of nacelle yaw misalignments (for example every 15° for 360°). A look-up table with the horizontal yaw bearing load for the range of wind-rotor misalignments investigated is created. The simplified model of the aerodynamic loads on the RNA consists of a fixed blade (or wing) segment located at the hub, where aerodynamic drag and lift coefficients can be specified. Using the look-up tables created using the detailed turbine model, drag and lift coefficients are estimated as a function of the angle between the rotor and the wind direction. This representation of the aerodynamic loading on the RNA was then verified against full-field turbulent wind simulations in fixed and floating conditions using a multi-megawatt commercial turbine. The results for the parameters concerning the floater, mooring and marine operations design were monitored (e.g. tower bottom loads, offsets, pitch, mooring tensions) for extreme conditions and the errors introduced by this simplified rotor are generally lower than 4%. This illustrates that this simplified representation of the turbine can be used by the various parties of the project during the early stages of the design, particularly when knowing the loading within the RNA and on higher sections of the tower is not important.

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