Vortex-Induced Vibration and Frequency Lock-In of an Airfoil at High Angles of Attack

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Fanny M. Besem ◽  
Joshua D. Kamrass ◽  
Jeffrey P. Thomas ◽  
Deman Tang ◽  
Robert E. Kielb
Keyword(s):  
Secondary Flows ◽  
Common Source ◽  
Structural Failure ◽  
Vortex Induced Vibration ◽  
Fluid Instability ◽  
Unsteady Force ◽  
Computational Fluid Dynamics Cfd ◽  
Shedding Frequency ◽  
Lock In ◽  
High Angles Of Attack

Vortex-induced vibration is a fluid instability where vortices due to secondary flows exert a periodic unsteady force on the elastic structure. Under certain circumstances, the shedding frequency can lock into the structure natural frequency and lead to limit cycle oscillations. These vibrations may cause material fatigue and are a common source of structural failure. This work uses a frequency domain, harmonic balance (HB) computational fluid dynamics (CFD) code to predict the natural shedding frequency and lock-in region of an airfoil at very high angles of attack. The numerical results are then successfully compared to experimental data from wind tunnel testings.

Vortex-Induced Vibration and Frequency Lock-In of an Airfoil at High Angles of Attack

2014 ◽  
Author(s):  
Fanny M. Besem ◽  
Joshua D. Kamrass ◽  
Jeffrey P. Thomas ◽  
Deman Tang ◽  
Robert E. Kielb
Keyword(s):  
High Amplitude ◽  
Secondary Flows ◽  
Common Source ◽  
Offshore Platforms ◽  
Vortex Induced Vibration ◽  
Naca0012 Airfoil ◽  
Unsteady Force ◽  
Shedding Frequency ◽  
Lock In ◽  
High Angles Of Attack

Vortex-induced vibration is a fluid instability present in many areas, including offshore platforms, wind turbines, and turbomachinery. The vortices due to secondary flows exert an periodic unsteady force on the elastic structure, leading to potentially dangerous vibrations. Under certain circumstances, the shedding frequency can lock into the structure natural frequency and lead to limit cycle oscillations. These high amplitude vibrations can cause material fatigue, and are a common source of structural failure. This work uses a frequency domain, harmonic balance, CFD code to predict the lock-in of an airfoil at very high angles of attack. The natural shedding frequency is found using a delta phase per iteration method, and the lock-in region is identified by enforcing airfoil motion at different oscillation amplitudes and frequencies. The numerical results are successfully compared to experimental data from wind tunnel testing on a NACA0012 airfoil at deep stall conditions.

Vortex Shedding and Frequency Lock in on Stand Still Wind Turbines: A Baseline Experiment

2017 ◽  
Author(s):  
Matthew Lennie ◽  
Alireza Selahi-Moghaddam ◽  
David Holst ◽  
Georgios Pechlivanoglou ◽  
Christian Navid Nayeri ◽  
...  
Keyword(s):  
Strouhal Number ◽  
Wind Turbines ◽  
Rotor Blades ◽  
Power Spectral ◽  
Vortex Induced Vibrations ◽  
Power Spectral Densities ◽  
Shedding Frequency ◽  
Lock In ◽  
Very High ◽  
High Angles Of Attack

During the commissioning and stand-still cycles of wind turbines, the rotor is often stopped or even locked leaving the rotor blades at a standstill. When the blades are at a stand still, angles of attack on the blades can be very high and it is therefore possible that they experience vortex induced vibrations. This experiment and analysis helps to explain the different regimes of flow at very high angles of attack, particularly on moderately twisted and tapered blades. A single blade was tested at two different flow velocities at a range of angles of attack with flow tuft visualisation and hotwire measurements of the wake. Hotwire wake measurements were able to show the gradual inception and ending of certain flow regimes. The power spectral densities of these measurements were normalized in terms of Strouhal number based on the projected chord to show that certain wake features have a relatively constant Strouhal number. The shedding frequency appears then to be relatively independent of chord taper and twist. Vortex generators were tested but were found to have little influence in this case. Gurney flaps were found to modify the wake geometry, stall onset angles and in some cases the shedding frequency.

Vortex Shedding and Frequency Lock in on Stand Still Wind Turbines—A Baseline Experiment

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Matthew Lennie ◽  
Alireza Selahi-Moghaddam ◽  
David Holst ◽  
George Pechlivanoglou ◽  
Christian Navid Nayeri ◽  
...  
Keyword(s):  
Strouhal Number ◽  
Wind Turbines ◽  
Rotor Blades ◽  
Power Spectral ◽  
Vortex Induced Vibrations ◽  
Power Spectral Densities ◽  
Shedding Frequency ◽  
Lock In ◽  
Very High ◽  
High Angles Of Attack

During the commissioning and stand-still cycles of wind turbines, the rotor is often stopped or even locked leaving the rotor blades at a standstill. When the blades are at a standstill, angles of attack on the blades can be very high, and it is therefore possible that they experience vortex-induced vibrations. This experiment and analysis helps to explain the different regimes of flow at very high angles of attack, particularly on moderately twisted and tapered blades. A single blade was tested at two different flow velocities at a range of angles of attack with flow tuft visualization and hotwire measurements of the wake. Hotwire wake measurements were able to show the gradual inception and ending of certain flow regimes. The power spectral densities of these measurements were normalized in terms of Strouhal number based on the projected chord to show that certain wake features have a relatively constant Strouhal number. The shedding frequency appears then to be relatively independent of chord taper and twist. Vortex generators (VGs) were tested but were found to have little influence in this case. Gurney flaps were found to modify the wake geometry, stall onset angles, and in some cases the shedding frequency.

Vortex-Induced Vibration of Horizontal Circular Cylinder in Uniform Flow

2004 ◽  
Author(s):  
Kentaroh Kokubun ◽  
Yasuhiro Wada
Keyword(s):  
Natural Frequency ◽  
Lift Coefficient ◽  
Vertical Displacement ◽  
Peak Frequency ◽  
Uniform Flow ◽  
Vortex Induced Vibration ◽  
Vortex Shedding Frequency ◽  
Nonlinear Form ◽  
Shedding Frequency ◽  
Lock In

This paper treats Vortex-Induced Vibration (VIV) of a cylinder in uniform flow. The cylinder is aluminum, rigid, circular, and 0.490 m in length, 0.025 m in diameter, and its weight is counterbalanced by buoyancy. The cylinder is horizontally mounted in a two-dimensional tank and allowed to move vertically by hanging through a spring during towing. The equation of motion of the structure is described in the nonlinear form and an approximate solution of the equation is obtained by using a vibrational theory. Lock-in phenomena appear when the vortex shedding frequency approaches to the natural frequency of the structure. Experimental results show that the oscillation of structure has remarkable two frequencies corresponding to the shedding frequency and the natural frequency of the structure. By using amplitude of vertical displacement at the top peak frequency, this paper proposes a way of estimating the transverse force, i.e., lift coefficient during VIV. The estimated lift coefficients are similar to the measured lift coefficients with the vertical displacement restricted to be zero. The estimated lift coefficients seem to be feasible.

CFD SIMULATION OF SHEAR STRESS AND SECONDARY FLOWS IN URETHRA

2007 ◽  
Vol 19 (02) ◽  
pp. 117-127 ◽  
Author(s):  
Yang-Yao Niu ◽  
Ding-Yu Chang
Keyword(s):  
Shear Stress ◽  
Cfd Simulation ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Normal Female ◽  
Urinary System ◽  
Stress Distributions ◽  
Computational Fluid Dynamics Cfd ◽  
Peak Value ◽  
Lower Urinary

In this work, a preliminary numerical simulation of the lower urinary system using Computational Fluid Dynamics (CFD) is performed. Very few studies have been done on the simulation of three-dimensional urine through the lower urinary system. In this study, a simplified lower urinary model with rigid body assumption is proposed. The distributions of urine flow velocity, wall pressure and shear stress along the urethra are simulated based on MRI scanned uroflowmetry of a normal female. Numerical results show that violent secondary flows appear on the cross surface near the end of the urethra when the inflow rate is increased. The oscillative variation of pressure and shear stress distributions are found around the beginning section of the urethra when flow rate is at the peak value.

Vortex Shedding Induced Dynamic Response of Marine Risers

1984 ◽  
Vol 106 (2) ◽  
pp. 214-221 ◽  
Author(s):  
F. Rajabi ◽  
M. F. Zedan ◽  
A. Mangiavacchi
Keyword(s):  
Dynamic Response ◽  
Vortex Shedding ◽  
Equation Of Motion ◽  
Continuous Beam ◽  
Regular Waves ◽  
Empirical Correlations ◽  
Fluid Resistance ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Lock In

An analytical model to predict the dynamic response of a riser in regular waves or in current to vortex shedding-induced lift forces is described. The riser is treated as a continuous beam under tension. A modal superposition scheme is used to solve the linearized equation of motion in the frequency domain. The excitation lift force is represented by a harmonic function with a frequency equal to the dominant vortex shedding frequency. Empirical correlations are used to determine the lift coefficients and shedding frequencies along the riser. Lift amplification is considered at or near the “lock-in” conditions. The fluid resistance to riser oscillations is represented by a Morison’s equation-type expression.

scholarly journals Numerical Study of Flow Characteristics Around Confined Cylinder using OpenFOAM

2018 ◽  
Vol 7 (4.35) ◽  
pp. 617
Author(s):  
P. Mathupriya ◽  
L. Chan ◽  
H. Hasini ◽  
A. Ooi
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Numerical Study ◽  
Vortex Formation ◽  
Plane Channel ◽  
Flow Characteristics ◽  
Strong Interactions ◽  
Two Dimensional ◽  
Computational Fluid Dynamics Cfd ◽  
Shedding Frequency

The numerical study of the flow over a two-dimensional cylinder which is symmetrically confined in a plane channel is presented to study the characteristics of vortex shedding. The numerical model has been established using direct numerical simulation (DNS) based on the open source computational fluid dynamics (CFD) code named OpenFOAM. In the present study, the flow fields have been computed at blockage ratio, β of 0.5 and at Reynolds number, Re of 200 and 300. Two-dimensional simulations investigated on the effects of Reynolds number based on the vortex formation and shedding frequency. It was observed that the presence of two distinct shedding frequencies appear at higher Reynolds number due to the confinement effects where there is strong interactions between boundary layer, shear layer and the wake of the cylinder. The range of simulations conducted here has shown to produce results consistent with that available in the open literature. Therefore, OpenFOAM is found to be able to accurately capture the complex physics of the flow.

Managing Vortex Induced Vibration in Well Jumper Systems

2008 ◽  
Author(s):  
Kenneth Bhalla ◽  
Lixin Gong
Keyword(s):  
Natural Frequency ◽  
Natural Frequencies ◽  
Cross Flow ◽  
Mitigation Measures ◽  
Mode Shapes ◽  
Bottom Current ◽  
Vortex Induced Vibration ◽  
Flow Response ◽  
Out Of Plane ◽  
Lock In

The purpose of this paper is to present a method that has been developed to identify if vortex induced vibration (VIV) occurs in well jumper systems. Moreover, a method has been developed to determine when VIV mitigation measures such as strakes are required. The method involves determining the in-plane and out-of-plane natural frequencies and mode shapes. The natural frequencies are then used, in conjunction with the maximum bottom current expected at a given location to determine if suppression is required. The natural frequency of a jumper system is a function of many variables, e.g. span length, leg height, pipe diameter and thickness, buoyancy placement, buoyancy uplift, buoyancy OD, insulation thickness, and contents of the jumper. The suppression requirement is based upon calculating a lower bound lock-in current speed based upon an assumed velocity bandwidth centered about the lock-in current. The out-of-plane VIV cross-flow response is produced by a current in the plane of the jumper; whereas the in-plane VIV cross-flow response is produced by the out-of-plane current. Typically, the out-of-plane natural frequency is smaller than the in-plane natural frequency. Jumpers with small spans have higher natural frequencies; thus small span jumpers may require no suppression or suppression on the vertical legs. Whereas, larger span jumpers may require no suppression, suppression on the vertical legs or suppression on all the legs. The span of jumper systems (i.e. production, water injection, gas lift/injection ...) may vary in one given field; it has become apparent that not all jumper systems require suppression. This technique has allowed us to recognize when certain legs of a given jumper system may require suppression, thus leading to a jumper design whose safety is not compromised while in the production mode, as well as minimizing downtime and identifying potential savings from probable fatigue failures.

Sign in / Sign up

Export Citation Format

Share Document