The effect of externally applied rotational oscillations on FIV characteristics of tandem circular cylinders for different spacing ratios

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Amir Hossein Rabiee ◽  
Mostafa Esmaeili
Keyword(s):  
Lift Coefficient ◽  
Oscillation Amplitude ◽  
Circular Cylinders ◽  
Feedback Signal ◽  
Flow Induced Vibration ◽  
Content Type ◽  
Spacing Ratio ◽  
Rotational Oscillations ◽  
Fluid Solid Interaction ◽  
Active Control Strategy

Purpose This study aims to explore an active control strategy for attenuation of in-line and transverse flow-induced vibration (FIV) of two tandem-arranged circular cylinders. Design/methodology/approach The control system is based on the rotary oscillation of cylinders around their axis, which acts according to the lift coefficient feedback signal. The fluid-solid interaction simulations are performed for two velocity ratios (V_r = 5.5 and 7.5), three spacing ratios (L/D = 3.5, 5.5 and 7.5) and three different control cases. Cases 1 and 2, respectively, deal with the effect of rotary oscillation of front and rear cylinders, while Case 3 considers the effect of applied rotary oscillation to both cylinders. Findings The results show that in Case 3, the FIV of both cylinders is perfectly reduced, while in Case 2, only the vibration of rear cylinder is mitigated and no change is observed in the vortex-induced vibration of front cylinder. In Case 1, by rotary oscillation of the front cylinder, depending on the reduced velocity and the spacing ratio values, the transverse oscillation amplitude of the rear cylinder suppresses, remains unchanged and even increases under certain conditions. Hence, at every spacing ratio and reduced velocity, an independent controller system for each cylinder is necessary to guarantee a perfect vibration reduction of front and rear cylinders. Originality/value The current manuscript seeks to deploy a type of active rotary oscillating (ARO) controller to attenuate the FIV of two tandem-arranged cylinders placed on elastic supports. Three different cases are considered so as to understand the interaction of these cylinders regarding the rotary oscillation.

Dynamic stall of an airfoil with different mounting angle of gurney flap

2020 ◽  
Vol 92 (7) ◽  
pp. 1037-1048
Author(s):  
Mehran Masdari ◽  
Milad Mousavi ◽  
Mojtaba Tahani
Keyword(s):  
Lift Coefficient ◽  
Oscillation Amplitude ◽  
Vertical Axis ◽  
Aerodynamic Performance ◽  
Dynamic Stall ◽  
Content Type ◽  
Naca0012 Airfoil ◽  
Gurney Flap ◽  
Stall Angle ◽  
Axis Length

Purpose One of the best methods to improve wind turbine aerodynamic performance is modification of the blade’s airfoil. The purpose of this paper is to investigate the effects of gurney flap geometry and its oscillation parameters on the pitching NACA0012 airfoil. Design/methodology/approach This numerical solution has been carried out for different cases of gurney flap mounting angles, heights, reduced frequencies and oscillation amplitudes, then the results were compared to each other. The finite volume method was used for the discretization of the governing equations, and the PISO algorithm was used to solve the equations. Also, the “SST” was adopted as the turbulence model in the simulation. Findings In this paper, the different parameters of gurney flap were investigated. The results showed that the best range of gurney flap height are between 1 and 3.2% of chord and the best ratio of lifting to drag coefficient is achieved in gurney flap with an angle of 90° relative to the chord direction. The dynamic stall angle of the airfoil with gurney flap decreases were compared to without gurney flap. Earlier LEV formation can be one of the main reasons for decreasing the dynamic stall angle of the airfoil with gurney flap. Increasing the reduced frequency and oscillation amplitude causes rising of maximum lift coefficient and consequently lift curve slope. Moreover, gurney flap with mounting angle has a lower hinge moment than the gurney flap without mounting angle but with the same vertical axis length. So, there is more complexity in structural design concerning the gurney flap without mounting angle. Practical implications Improving aerodynamic efficiency of airfoils is vital for obtaining more output power in VAWTs. Gurney flaps are one of the best mechanisms to increase the aerodynamic performance of the airfoil and increases the efficiency of VAWTs. Originality/value Investigating the hinge moment on the connection point of the airfoil, gurney flap and try to compare the gurney flap with and without angle.

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.

scholarly journals Numerical Investigation on Vortex-Induced Vibration Energy Extraction Efficiency of Double Circular Cylinders In Tandem Arrangement at Low Reynolds Number

2018 ◽  
Vol 153 ◽  
pp. 05001
Author(s):  
Wu Junwu ◽  
Yin Zhongjun
Keyword(s):  
Reynolds Number ◽  
Bluff Body ◽  
Extraction Efficiency ◽  
Low Flow ◽  
Circular Cylinders ◽  
Energy Extraction ◽  
Flow Induced Vibration ◽  
Spacing Ratio ◽  
Mass Coefficient ◽  
Simulated Flow

Vortex shedding from a bluff body results in fluctuating forces acting on the bluff body, which may induce vibration of the bluff body when the bluff body is elastically mounted or deformable. Researchers put forward an idea that we can ex-tract energy from the water flow based on VIV at low flow velocity. Although plenty of researches on parameters of VIV are already presented, however, the improvement of energy extraction efficiency still needs further study. According to the previous research, this essay has simulated flow-induced vibration of tandem double circular cylinders when Reynolds number is 100. Working condition has been considered as the fixed upstream cylinder and the free vibration of the downstream cylinder. The influence of the mass coefficient and the two cylinders spacing ratio on the downstream cylinder’s energy obtained from the fluid is studied. Analysis results show that, the maximum value of the energy extraction efficiency is before the frequency locked range. In the case of large spacing ratio (L/D=7~9), the phenomenon of "beat vibration" appears on the downstream cylinder. The results of this work could provide reference for the improvement of energy extraction efficiency and the design of VIV converter.

Two-degree-of-freedom flow-induced vibration of two circular cylinders with constraint for different arrangements

2021 ◽  
Vol 225 ◽  
pp. 108806
Author(s):  
Qunfeng Zou ◽  
Lin Ding ◽  
Rui Zou ◽  
Hao Kong ◽  
Haibo Wang ◽  
...  
Keyword(s):  
Degree Of Freedom ◽  
Circular Cylinders ◽  
Flow Induced Vibration ◽  
Two Degree Of Freedom

scholarly journals Buoyancy Effect on the Flow Pattern and the Thermal Performance of an Array of Circular Cylinders

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Francesco Fornarelli ◽  
Antonio Lippolis ◽  
Paolo Oresta
Keyword(s):  
Nusselt Number ◽  
Flow Pattern ◽  
Richardson Number ◽  
Near Field ◽  
Circular Cylinders ◽  
Momentum Exchange ◽  
Force Coefficients ◽  
The Earth ◽  
Spacing Ratio ◽  
Oscillatory Character

In this paper, we found, by means of numerical simulations, a transition in the oscillatory character of the flow field for a particular combination of buoyancy and spacing in an array of six circular cylinders at a Reynolds number of 100 and Prandtl number of 0.7. The cylinders are isothermal and they are aligned with the earth acceleration (g). According to the array orientation, an aiding or an opposing buoyancy is considered. The effect of natural convection with respect to the forced convection is modulated with the Richardson number, Ri, ranging between −1 and 1. Two values of center-to-center spacing (s = 3.6d–4d) are considered. The effects of buoyancy and spacing on the flow pattern in the near and far field are described. Several transitions in the flow patterns are found, and a parametric analysis of the dependence of the force coefficients and Nusselt number with respect to the Richardson number is reported. For Ri=−1, the change of spacing ratio from 3.6 to 4 induces a transition in the standard deviation of the force coefficients and heat flux. In fact, the transition occurs due to rearrangement of the near-field flow in a more ordered wake pattern. Therefore, attention is focused on the influence of geometrical and buoyancy parameters on the heat and momentum exchange and their fluctuations. The available heat exchange models for cylinders array provide a not accurate prediction of the Nusselt number in the cases here studied.

Numerical Simulation for Flow over Two Circular Cylinders in Micro Channel with Lattice Boltzmann Method

2014 ◽  
Vol 670-671 ◽  
pp. 747-750
Author(s):  
Zhi Jun Gong ◽  
Jiao Yang ◽  
Wen Fei Wu
Keyword(s):  
Lattice Boltzmann Method ◽  
Lattice Boltzmann ◽  
Recirculation Zone ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Micro Channel ◽  
Zone Length ◽  
Spacing Ratio ◽  
Boltzmann Method

For indepth study on flow characteristics for fluid bypass obstacles in micro-channel, the Lattice Boltzmann Method (LBM) was used to simulate fluid flow over two circular cylinders in side-by-side arrangement of a micro-channel. The velocity distribution and recirculation zone length under different Reynolds numbers (Re = 0~100) and different spacing ratio (H/D= 0~2.0) were obtained. The results show that the pattern of flow and the size of recirculation zone in the micro-channel depend on the combined effect of Re and H/D.

Experimental study of a pitching and plunging wing

2018 ◽  
Vol 90 (7) ◽  
pp. 1136-1144 ◽  
Author(s):  
Dimitris Gkiolas ◽  
Demetri Yiasemides ◽  
Demetri Mathioulakis
Keyword(s):  
Experimental Data ◽  
Flow Visualization ◽  
Wind Turbine ◽  
Flow Separation ◽  
Flow Behavior ◽  
Lift Coefficient ◽  
Turbine Blades ◽  
Content Type ◽  
Separation Line ◽  
Wing Chord

Purpose The complex flow behavior over an oscillating aerodynamic body, e.g. a helicopter rotor blade, a rotating wind turbine blade or the wing of a maneuvering airplane involves combinations of pitching and plunging motions. As the parameters of the problem (Re, St and phase difference between these two motions) vary, a quasi-steady analysis fails to provide realistic results for the aerodynamic response of the moving body, whereas this study aims to provide reliable experimental data. Design/methodology/approach In the present study, a pitching and plunging mechanism was designed and built in a subsonic closed-circuit wind tunnel as well as a rectangular aluminum wing of a 2:1 aspect-ratio with a NACA64-418 airfoil, used in wind turbine blades. To measure the pressure distribution along the wing chord, a number of fast responding transducers were embedded into the mid span wing surface. Simultaneous pressure measurements were conducted along the wing chord for the Reynolds number of 0.85 × 106 for both steady and unsteady cases (pitching and plunging). A flow visualization technique was used to detect the flow separation line under steady conditions. Findings Elevated pressure fluctuations coincide with the flow separation line having been detected through surface flow visualization and flattened pressure distributions appear downstream of the flow separation line. Closed hysteresis loops of the lift coefficient versus angle of attack were measured for combined pitching and plunging motions. Practical implications The experimental data can be used for improvement of unsteady fluid mechanics problem solvers. Originality/value In the present study, a new installation was built allowing the aerodynamic study of oscillating wings performing pitching and plunging motions with prescribed frequencies and phase lags between the two motions. The experimental data can be used for improvement of computational fluid dynamics codes in case that the examined aerodynamic body is oscillating.

Dual-position excitation technique in flow control over an airfoil at low speeds

2018 ◽  
Vol 30 (9) ◽  
pp. 4141-4154
Author(s):  
Abbas Ebrahimi ◽  
Majid Hajipour ◽  
Kamran Ghamkhar
Keyword(s):  
Flow Control ◽  
Shear Layer ◽  
Control Method ◽  
Lift Coefficient ◽  
Shear Layers ◽  
Control Flow ◽  
Plasma Actuators ◽  
Dbd Plasma ◽  
Surface Shear ◽  
Content Type

PurposeThe purpose of this paper is to control flow separation over a NACA 4415 airfoil by applying unsteady forces to the separated shear layers using dielectric barrier discharge (DBD) plasma actuators. This novel flow control method is studied under conditions which the airfoil angle of attack is 18°, and Reynolds number based on chord length is 5.5 × 105.Design/methodology/approachLarge eddy simulation of the turbulent flow is used to capture vortical structures through the airfoil wake. Power spectral density analysis of the baseline flow indicates dominant natural frequencies associated with “shear layer mode” and “wake mode.” The wake mode frequency is used simultaneously to excite separated shear layers at both the upper surface and the trailing edge of the airfoil (dual-position excitation), and it is also used singly to excite the upper surface shear layer (single-position excitation).FindingsBased on the results, actuations manipulate the shear layers instabilities and change the wake patterns considerably. It is revealed that in the single-position excitation case, the vortices shed from the upper surface shear layer are more coherent than the dual-position excitation case. The maximum value of lift coefficient and lift-to-drag ratio is achieved, respectively, by single-position excitation as well as dual-position excitation.Originality/valueThe paper contributes to the understanding and progress of DBD plasma actuators for flow control applications. Further, this research could be a beneficial solution for the promising design of advanced low speed flying vehicles.

Surface Roughness Effects on Circular Cylinders at High Reynolds Numbers

2002 ◽  
Author(s):  
M. Eaddy ◽  
W. H. Melbourne ◽  
J. Sheridan
Keyword(s):  
Surface Roughness ◽  
Reynolds Numbers ◽  
Circular Cylinders ◽  
Flow Induced Vibration ◽  
Roughness Effects ◽  
Vortex Induced Vibration ◽  
Smooth Cylinder ◽  
Lift Forces ◽  
High Reynolds ◽  
Effect Of Surface

The problem of flow-induced vibration has been studied extensively. However, much of this research has focused on the smooth cylinder to gain an understanding of the mechanisms that cause vortex-induced vibration. In this paper results of an investigation of the effect of surface roughness on the cross-wind forces are presented. Measurements of the sectional RMS fluctuating lift forces and the axial correlation of the pressures for Reynolds numbers from 1 × 105 to 1.4 × 106 are given. It was found that surface roughness significantly increased the axial correlation of the pressures to similar values found at high subcritical Reynolds numbers. There was little effect of the surface roughness on the sectional lift forces. The improved correlation of the vortex shedding means rough cylinders will be subject to larger cross-wind forces and an increased possibility of vortex-induced vibration compared to smooth cylinders.

scholarly journals Effect of Cylinder Gap Ratio on The Wake of a Circular Cylinder Enclosed by Various Perforated Shrouds

CFD letters ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 51-68
Author(s):  
Nurul Azihan Ramli ◽  
Azlin Mohd Azmi ◽  
Ahmad Hussein Abdul Hamid ◽  
Zainal Abidin Kamarul Baharin ◽  
Tongming Zhou
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Vortex Shedding ◽  
Control Method ◽  
Lift Coefficient ◽  
Base Case ◽  
Bluff Bodies ◽  
Ansys Fluent ◽  
Gap Ratio ◽  
Spacing Ratio

Flow over bluff bodies produces vortex shedding in their wake regions, leading to structural failure from the flow-induced forces. In this study, a passive flow control method was explored to suppress the vortex shedding from a circular cylinder that causes many problems in engineering applications. Perforated shrouds were used to control the vortex shedding of a circular cylinder at Reynolds number, Re = 200. The shrouds were of non-uniform and uniform holes with 67% porosity. The spacing gap ratio between the shroud and the cylinder was set at 1.2, 1.5, 2, and 2.2. The analysis was conducted using ANSYS Fluent using a viscous laminar model. The outcomes of the simulation of the base case were validated with existing studies. The drag coefficient, Cd, lift coefficient, Cl and the Strouhal number, St, as well as vorticity contours, velocity contours, and pressure contours were examined. Vortex shedding behind the shrouded cylinders was observed to be suppressed and delayed farther downstream with increasing gap ratio. The effect was significant for spacing ratio greater than 2.0. The effect of hole types: uniform and non-uniform holes, was also effective at these spacing ratios for the chosen Reynolds number of 200. Specifically, a spacing ratio of 1.2 enhanced further the vortex intensity and should be avoided.

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