Vortex shedding from circular and noncircular bodies at high angles of attack

1979 ◽  
Author(s):  
M. MENDENHALL ◽  
S. SPANGLER ◽  
S. PERKINS, JR.
Keyword(s):  
Vortex Shedding ◽  
High Angles Of Attack

A computational study of vortex shedding from a NACA-0012 airfoil at high angles of attack

2018 ◽  
Vol 6 (1) ◽  
pp. 1 ◽  
Author(s):  
Mohamed Y. Zakaria ◽  
Mostafa M. Ibrahim ◽  
Saad Ragab ◽  
Muhammad R. Hajj
Keyword(s):  
Vortex Shedding ◽  
Computational Study ◽  
Naca 0012 ◽  
High Angles Of Attack

scholarly journals Development of a second-order dynamic stall model

2020 ◽  
Vol 5 (2) ◽  
pp. 577-590 ◽  
Author(s):  
Niels Adema ◽  
Menno Kloosterman ◽  
Gerard Schepers
Keyword(s):  
Vortex Shedding ◽  
Turbine Blades ◽  
Second Order ◽  
Dynamic Stall ◽  
Small Scale ◽  
Wind Turbine Blades ◽  
Extreme Loads ◽  
Cost Efficient ◽  
Improved Model ◽  
High Angles Of Attack

Abstract. Dynamic stall phenomena carry the risk of negative damping and instability in wind turbine blades. It is crucial to model these phenomena accurately to reduce inaccuracies in predicting design driving (fatigue and extreme) loads. Some of the inaccuracies in current dynamic stall models may be due to the fact that they are not properly designed for high angles of attack and that they do not specifically describe vortex shedding behaviour. The Snel second-order dynamic stall model attempts to explicitly model unsteady vortex shedding. This model could therefore be a valuable addition to a turbine design software such as Bladed. In this paper the model has been validated with oscillating aerofoil experiments, and improvements have been proposed for reducing inaccuracies. The proposed changes led to an overall reduction in error between the model and experimental data. Furthermore the vibration frequency prediction improved significantly. The improved model has been implemented in Bladed and tested against small-scale turbine experiments at parked conditions. At high angles of attack the model looks promising for reducing mismatches between predicted and measured (fatigue and extreme) loading, leading to possible lower safety factors for design and more cost-efficient designs for future wind turbines.

Vortex Shedding Lock-In due to Stream-Wise Oscillation of a 2-D Wind Turbine Blade Section at High Angles of Attack

2014 ◽  
Author(s):  
Alberto Pellegrino ◽  
Craig Meskell
Keyword(s):  
Wind Turbine ◽  
Turbine Blade ◽  
Vortex Shedding ◽  
Bluff Body ◽  
Oscillation Amplitude ◽  
Wind Turbine Blade ◽  
Sst Turbulence Model ◽  
Blade Section ◽  
Lock In ◽  
High Angles Of Attack

The unsteady, incompressible flow around a translating two-dimensional wind turbine blade section (NREL S809) in the stream-wise direction has been simulated using unsteady RANS with the transition SST turbulence model. The Reynolds number is Re = 106 referred to a chord length of 1 m. A prescribed sinusoidal stream-wise motion has been applied at a fixed amplitude of 0.25 m for a range of high angles of attack [30° < α < 150°]. At these incidences, the airfoil will behave more like a bluff body and may experience periodic vortex shedding. It is well known that oscillations can lead to a synchronization (lock-in) of the vortex shedding frequency, fv, with the body’s motion frequency, fs, in bluff body flows. In order to investigate the susceptibility of the wind turbine blade section to lock-in, a parametric study has been conducted varying the frequency ratio r, (r = fs/fv0), in a range around r = 1 and r = 0.5. The lock-in region boundaries have been proposed and an analysis of the effect of the oscillation amplitude has been conducted. The synchronization map obtained suggests that, for the vibration amplitude considered, the risk of vortex-induced vibration is more significant in the regions of α = 35° and α = 145°. Furthermore, it has been found that for some stream-wise amplitudes, increasing the oscillation amplitude, lock-in appears to be unexpectedly suppressed in the vicinity of r = 1.

scholarly journals Vortex Shedding Lock-In due to Pitching Oscillation of a Wind Turbine Blade Section at High Angles of Attack

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Craig Meskell ◽  
Alberto Pellegrino
Keyword(s):  
Wind Turbine ◽  
Turbine Blade ◽  
Vortex Shedding ◽  
Bluff Body ◽  
Oscillation Amplitude ◽  
Wind Turbine Blade ◽  
Wake Oscillator ◽  
Sst Turbulence Model ◽  
Lock In ◽  
High Angles Of Attack

The unsteady flow around a pitching two-dimensional airfoil section (NREL S809) has been simulated using unsteady RANS with the transition SST turbulence model. This geometry is chosen to represent a wind turbine blade in a standstill configuration. The Reynolds number is Re=106 based on a chord length of 1 m. A prescribed sinusoidal pitching motion has been applied at a fixed amplitude of 7° for a range of high angles of attack 30°<α<150°. At these incidences, the airfoil will behave more like a bluff body and may experience periodic vortex shedding. It is well known that, in bluff body flows, oscillations can lead to a lock-in (lock-in) of the vortex shedding frequency, fv, with the body’s motion frequency, fp. In order to investigate the susceptibility of airfoil to lock-in, the frequency ratio r (r=fp/fv0) has been varied around r=1. The lock-in region boundaries have been proposed, and an analysis of the effect of the oscillation amplitude has been conducted. The lock-in map obtained suggests that, for the vibration amplitude considered, the risk of vortex-induced vibration is more significant in the regions of α≈40° and α≈140°, i.e., for shallower characteristic lengths. Finally, a lumped parameter wake oscillator model has been proposed for pitching airfoils. This simple model is in qualitative agreement with the CFD results.

A computational study of vortex shedding from a NACA-0012 airfoil at high angles of attack

2018 ◽  
Vol 6 (1) ◽  
pp. 1
Author(s):  
Saad Ragab ◽  
Muhammad R. Hajj ◽  
Mostafa M. Ibrahim ◽  
Mohamed Y. Zakaria
Keyword(s):  
Vortex Shedding ◽  
Computational Study ◽  
Naca 0012 ◽  
High Angles Of Attack

scholarly journals Development of a Second Order Dynamic Stall Model

2019 ◽  
Author(s):  
Niels Adema ◽  
Menno Kloosterman ◽  
Gerard Schepers
Keyword(s):  
Vortex Shedding ◽  
Turbine Blades ◽  
Fatigue Loading ◽  
Second Order ◽  
Dynamic Stall ◽  
Small Scale ◽  
Wind Turbine Blades ◽  
Cost Efficient ◽  
Improved Model ◽  
High Angles Of Attack

Abstract. Dynamic stall phenomena bring risk for negative damping and instability in wind turbine blades. It is crucial to model these phenomena accurately to reduce inaccuracies in predicting design driving (fatigue) loads. Inaccuracies in current dynamic stall models may be due to the facts that they are not properly designed for high angles of attack, and that they do not specifically describe vortex shedding behaviour. The Snel second order dynamic stall model attempts to explicitly model unsteady vortex shedding. This model could therefore be a valuable addition to DNV GL's turbine design software Bladed. In this thesis the model has been validated with oscillating airfoil experiments and improvements have been proposed for reducing inaccuracies. The proposed changes led to an overall reduction in error between the model and experimental data. Furthermore the vibration frequency prediction improved significantly. The improved model has been implemented in Bladed and tested against small scale turbine experiments at parked conditions. At high angles of attack the model looks promising for reducing mismatches between predicated and measured (fatigue) loading. Leading to possible lower safety factors for design and more cost efficient designs for future wind turbines.

Evolution of unstable system.

2015 ◽  
Vol 9 (3) ◽  
pp. 2487-2502 ◽  
Author(s):  
Igor V. Lebed
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Stokes Flow ◽  
Stable Solution ◽  
The State ◽  
Unstable System ◽  
Unstable Flow ◽  
Unstable Solutions ◽  
Vortex Shedding Modes ◽  
Hydrodynamics Equations

Scenario of appearance and development of instability in problem of a flow around a solid sphere at rest is discussed. The scenario was created by solutions to the multimoment hydrodynamics equations, which were applied to investigate the unstable phenomena. These solutions allow interpreting Stokes flow, periodic pulsations of the recirculating zone in the wake behind the sphere, the phenomenon of vortex shedding observed experimentally. In accordance with the scenario, system loses its stability when entropy outflow through surface confining the system cannot be compensated by entropy produced within the system. The system does not find a new stable position after losing its stability, that is, the system remains further unstable. As Reynolds number grows, one unstable flow regime is replaced by another. The replacement is governed tendency of the system to discover fastest path to depart from the state of statistical equilibrium. This striving, however, does not lead the system to disintegration. Periodically, reverse solutions to the multimoment hydrodynamics equations change the nature of evolution and guide the unstable system in a highly unlikely direction. In case of unstable system, unlikely path meets the direction of approaching the state of statistical equilibrium. Such behavior of the system contradicts the scenario created by solutions to the classic hydrodynamics equations. Unstable solutions to the classic hydrodynamics equations are not fairly prolonged along time to interpret experiment. Stable solutions satisfactorily reproduce all observed stable medium states. As Reynolds number grows one stable solution is replaced by another. They are, however, incapable of reproducing any of unstable regimes recorded experimentally. In particular, stable solutions to the classic hydrodynamics equations cannot put anything in correspondence to any of observed vortex shedding modes. In accordance with our interpretation, the reason for this isthe classic hydrodynamics equations themselves.

Some modeling issues on trailing-edge vortex shedding

AIAA Journal ◽  
2001 ◽  
Vol 39 ◽  
pp. 787-793
Author(s):  
Wei Ning ◽  
Li He
Keyword(s):  
Vortex Shedding ◽  
Trailing Edge ◽  
Edge Vortex
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