“…It should be noted that the low porosity of the perforations () resulted in minimal changes to the backward flow region where , in contrast to the significant backward flow region reduction observed in plates with high porosity (Jin et al. 2020). Figure 6.Measured time-averaged streamwise velocity fields around the (solid), and flexible plates under , 5 and 8 m s.…”
Section: Resultsmentioning
confidence: 94%
“…Additionally, the aspect ratio of the plate, and , minimizes the influence of the Poisson ratio (Jin et al. 2020).…”
Section: Experimental Set-upmentioning
confidence: 99%
“…The gravitational and elastic restoring forces ratio, (Luhar & Nepf 2011; Jin et al. 2020), show some gravitational effect on the plate deformation. We characterized the aerodynamic force and reconfiguration of each plate at 16 incoming velocities, , ranging from 2 to 10 m s at intervals of m s.…”
Section: Experimental Set-upmentioning
confidence: 99%
“…The minimum drag scenario had an uncertainty of approximately 3 % (Jin et al. 2020). To capture the deformation and vibration of the plates, a two-dimensional particle tracking velocimetry (PTV) technique was employed on 20 fiducial points equally distributed on the side of each acrylic plate.…”
The effect of single perforations and their location on the drag and reconfiguration of flexible plates was explored through laboratory experiments and direct numerical simulations. The plates were subjected to uniform flows with negligible turbulence, and the perforations had a square cross-section resulting in a low porosity ratio of
$\gamma \approx 0.028$
. Rigid plates with and without perforations and flexible plates without perforations served as the baseline cases. The perforated plates exhibited distinct jets through the openings in the wake, significantly impacting the aerodynamic force and plate deformation. The velocity and position of the centre jet velocity in relation to downwind distance were influenced by both the incoming flow and the location of the perforations. The centre jet velocity profiles were normalized using an effective velocity and corrected perforation half-width, revealing their dependence on these factors. A simple first-order formulation was developed to predict the change in drag for various perforated plates under a wide range of incoming velocities. This formulation was supported by numerical simulations across a wider range of Cauchy number to confirm the proposed model and separate the effect of the Cauchy and Reynolds numbers. The results of this study may inform the design of flexible structures, define effective porosity and serve as an initial step towards modelling the complex interaction between flow and structures with low porosity.
“…It should be noted that the low porosity of the perforations () resulted in minimal changes to the backward flow region where , in contrast to the significant backward flow region reduction observed in plates with high porosity (Jin et al. 2020). Figure 6.Measured time-averaged streamwise velocity fields around the (solid), and flexible plates under , 5 and 8 m s.…”
Section: Resultsmentioning
confidence: 94%
“…Additionally, the aspect ratio of the plate, and , minimizes the influence of the Poisson ratio (Jin et al. 2020).…”
Section: Experimental Set-upmentioning
confidence: 99%
“…The gravitational and elastic restoring forces ratio, (Luhar & Nepf 2011; Jin et al. 2020), show some gravitational effect on the plate deformation. We characterized the aerodynamic force and reconfiguration of each plate at 16 incoming velocities, , ranging from 2 to 10 m s at intervals of m s.…”
Section: Experimental Set-upmentioning
confidence: 99%
“…The minimum drag scenario had an uncertainty of approximately 3 % (Jin et al. 2020). To capture the deformation and vibration of the plates, a two-dimensional particle tracking velocimetry (PTV) technique was employed on 20 fiducial points equally distributed on the side of each acrylic plate.…”
The effect of single perforations and their location on the drag and reconfiguration of flexible plates was explored through laboratory experiments and direct numerical simulations. The plates were subjected to uniform flows with negligible turbulence, and the perforations had a square cross-section resulting in a low porosity ratio of
$\gamma \approx 0.028$
. Rigid plates with and without perforations and flexible plates without perforations served as the baseline cases. The perforated plates exhibited distinct jets through the openings in the wake, significantly impacting the aerodynamic force and plate deformation. The velocity and position of the centre jet velocity in relation to downwind distance were influenced by both the incoming flow and the location of the perforations. The centre jet velocity profiles were normalized using an effective velocity and corrected perforation half-width, revealing their dependence on these factors. A simple first-order formulation was developed to predict the change in drag for various perforated plates under a wide range of incoming velocities. This formulation was supported by numerical simulations across a wider range of Cauchy number to confirm the proposed model and separate the effect of the Cauchy and Reynolds numbers. The results of this study may inform the design of flexible structures, define effective porosity and serve as an initial step towards modelling the complex interaction between flow and structures with low porosity.
“…18,19 In particular, the observations of Vogel 20,21 demonstrated that the deformation of some parts of plants leads to lower values of drag force F x and showed that the relationship between drag and velocity follows the scaling F x / U 2þc , where c is a negative exponent. The reconfiguration of flexible structures has been extensively analyzed in applications concerning thin plates and filaments placed transversely to the flow stream, [22][23][24][25][26][27][28] where the reduction of the drag is associated with the streamlining of the bodies and the reduction of the exposed area. In view of these studies, the use of flexible structures, able to adapt to the flow, seems an interesting solution if a quasi-static streamlining of blunt bodies is sought.…”
We investigate the quasi-static reconfiguration of rear parallel flexible plates on the drag coefficient of a blunt body. The drag coefficient, plates deformation, and main features of the turbulent wake are characterized experimentally in a towing tank. It is found that increasing the flexibility of plates leads to an important drag reduction, induced by the progressive streamlining of the trailing edge due to plates deformation. The study of the Vogel exponent is adopted here to evaluate the limit on the potential drag reduction at large values of the Cauchy number, which is shown to be mainly caused by the growth in the vibrating amplitude response of plates. The plates deformation is analyzed by means of image processing, showing that their shapes mainly follow the first modal form of a cantilever beam deflection, although a slight concavity develops toward the plates tip for large Cauchy numbers. To further analyze this process, the empirical flow loading along the plates is estimated by a modified beam theory assuming a distributed load given by a power law. The experimental fitting shows that for large flexibility, the load diminishes at the rear tip. Besides, the progressive deformation of plates is shown to weaken the shedding of vortices and reduce the size of the recirculation bubble. Finally, an affine direct relationship between recirculation bubble aspect ratio and drag coefficient has been proposed in order to quantify the linkage between near wake modifications and hydrodynamic improvement provided by the trailing edge streamlining.
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