Data-driven stability analysis and near-wake jet control for the vortex-induced vibration of a sphere

2021 ◽  
Vol 33 (4) ◽  
pp. 044104
Author(s):  
Amir Chizfahm ◽  
Rajeev Jaiman
Keyword(s):  
Stability Analysis ◽  
Data Driven ◽  
Near Wake ◽  
Vortex Induced Vibration ◽  
Jet Control

A Double Birkhoff Wake Oscillator for the Modeling of Vortex-Induced Vibration

2011 ◽  
Author(s):  
R. H. M. Ogink
Keyword(s):  
Free Vibration ◽  
Added Mass ◽  
Mass Force ◽  
Near Wake ◽  
Vibration Measurements ◽  
Vortex Induced Vibration ◽  
Fluid Forces ◽  
Wake Oscillator ◽  
Model Equations ◽  
Far Wake

A double Birkhoff wake oscillator for the modeling of vortex-induced vibration is presented in which the oscillating variables are assumed to be associated with the boundary layer/near wake and the far wake. The fluid forces are assumed to consist of a potential added mass force and a force due to vortex shedding. In the limit of vanishing incoming flow velocity, the model equations reduce to a form similar to the Morison equation. The results of the double wake oscillator have been compared with forced vibration measurements and free vibration measurements over a range of mass and damping ratios. The model is capable of describing the most important trends in both the forced and free vibration experiments. Specifically, the double wake oscillator is able to model both the upper and lower branch of free vibration.

Stability analysis of data-driven local model networks

2013 ◽  
Vol 20 (3) ◽  
pp. 224-247 ◽  
Author(s):  
Christoph Hametner ◽  
Christian H. Mayr ◽  
Martin Kozek ◽  
Stefan Jakubek
Keyword(s):  
Stability Analysis ◽  
Data Driven ◽  
Local Model ◽  
Local Model Networks ◽  
Model Networks

On the origin of the secondary vortex street

2012 ◽  
Vol 711 ◽  
pp. 641-666 ◽  
Author(s):  
Bhaskar Kumar ◽  
Sanjay Mittal
Keyword(s):  
Stability Analysis ◽  
Linear Stability ◽  
Vortex Shedding ◽  
Linear Stability Analysis ◽  
Broad Band ◽  
Vortex Street ◽  
Secondary Vortex ◽  
Primary Vortex ◽  
Near Wake ◽  
Far Wake

AbstractThe origin of the secondary vortex street, observed in the far wake in the flow past a circular cylinder, is investigated. The Reynolds number, based on the diameter of the cylinder, is 150. The von Kármán vortex street, which originates in the near wake, decays exponentially downstream of the cylinder. Beyond the region of decay, a broad band of frequencies are selectively amplified, leading to the formation of a secondary vortex street consisting of packets of large-scale vortex structures. The streamwise location of the onset of the instability, frequency of the generation of packets and their convection speed are estimated via direct numerical simulation (DNS). Global linear stability analysis of the time-averaged flow reveals the presence of unstable convective modes that travel at almost the same speed and have a structure similar to the packet-like disturbances as observed in the DNS. Sensitivity analysis of the global convective modes to structural perturbations is carried out to locate the region of the wake that is most significant in generating the modes responsible for the appearance of the secondary vortex street. This information is utilized to control the flow. By placing a ‘slip’ splitter plate along the wake centre line, in the overlap region of the direct and the adjoint modes, the oscillations in the far wake are significantly reduced, though the oscillations related to the primary vortex shedding in the near wake are not. It is also found that suppression of the primary vortex shedding leads to annihilation of the secondary vortex street as well. Linear stability analysis of the steady-state flow does not yield any modes that can explain the appearance of the secondary vortex street. The steady and time-averaged wake profiles, for the $\mathit{Re}= 150$ flow, are compared to bring out the differences in the two. The effect of free-stream oscillations on the evolution of the secondary vortex street is investigated. By reducing the amplitude of inlet excitation, a gradual transition from ordered shedding in the far wake to the appearance of a broad-band spectrum of frequencies, as in the unforced wake, is observed. All the computations have been carried out using a stabilized finite element method.

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