@misc{10481/100665,
year = {2020},
month = {11},
url = {https://hdl.handle.net/10481/100665},
abstract = {We present a numerical study on the fluid–structure interaction of an incompressible
laminar flow around a slender blunt-based body implementing a rear cavity of flexible
plates. The study focuses on the use of this type of device to control the wake dynamics
and the aerodynamic forces acting on the body, as well as to harvest energy from
the flow. To that aim, the effects on the plates flow-induced vibrations (FIV) and on
the dynamics of the flow of three control parameters, namely the reduced velocity,
0 ≤ U^∗ < 12, the mass ratio, m^∗ = [500, 1000] and the cavity height h_c , are evaluated at
Reynolds number Re = 500. Four different branches are identified in terms of dynamic
response, as U^∗ increases, regardless of the values of hc and m^∗. At low values of U^∗,
an initial branch with a local peak of moderate amplitude response is observed, where
the plates oscillate in counter-phase, in a varicose mode, with a frequency f_p that is
synchronized with the second harmonic of the vortex shedding frequency, 2 f_{vs}, and
similar to the natural frequency of the solid, f_n ≃ f_{1,n}. For intermediate values of U^∗,
a transition towards a sinuous mode of oscillation occurs, where the plate frequency is
synchronized with the vortex shedding frequency, f_p = f_{vs}. Initially, after such transition,
the oscillation frequency is lower than the natural frequency of the plates f_p < f_{1,n}, so
that a weak response defines a lower branch in the amplitude response curve. When
U_∗ increases, a lock-in regime develops with f_p = f_{vs} = f_{1,n}, that is characterized by a
response amplification, giving rise to the emergence of the upper branch, where the
FIV amplitude of plates is the highest. Finally, a fourth desynchronization branch of
moderate amplitude appears for larger values of U^∗, where the plates present a complex,
multi-mode regime, characterized by the vibration at multiple frequencies within the
range 5 f_{1,n} < f_p < 6.5 f_{1,n}. The analysis of the plates deformation through POD analysis
reveals that they mainly oscillate following the first Euler–Bernoulli mode for the first
three branches, and a combination of the second and first Euler–Bernoulli modes for
the desynchronization branch. The effect of increasing the mass ratio is to mitigate
the response at higher values of U^∗, while reducing the cavity height h_c leads to the
fostering of oscillations within the upper and desynchronization branches. In general,
the FIV response of plates alters the wake dynamics and the force coefficient, especially
within the lock-in regime, where the drag is strongly amplified, although the fluctuations
of the lift are attenuated (nearly a 40% reduction). Besides, reductions of the drag of
approximately 2% are obtained within the initial and lower branches. Finally, a simple
quantification of the energy transfer from the plates, through a linearized Euler–Bernoulli},
organization = {Spanish MICINN and European Funds under Project DPI2017-89746-R},
keywords = {Drag reduction},
keywords = {Bluff body},
keywords = {Passive control},
keywords = {Flexible flap},
keywords = {Self-adaptive flap},
keywords = {Fluid-structure interaction},
title = {Numerical analysis of the flow-induced vibrations in the laminar wake behind a blunt body with rear flexible cavities},
doi = {https://doi.org/10.1016/j.jfluidstructs.2020.103194},
author = {García-Baena, Carlos and Jiménez-González, José Ignacio and Gutiérrez-Montes, Cándido and Martínez-Bazán, Carlos},
}