Flow-structure interactions of two tandem inverted flags in a water tunnel

Hu, Yao-Wei; Feng, Li-Hao; Wang, Jinjun

doi:10.1063/5.0012544

Cited by 9 publications

(5 citation statements)

References 35 publications

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“…Recently, the concurrent operation of two or more inverted flags has started to gain attention, with two main configurations being considered: side-by-side (see Figure 1 b) [ 45 , 46 , 47 , 48 , 49 , 50 , 51 ] and tandem (see Figure 1 b) [ 51 , 52 , 53 ] configurations within the horizontal plane. Huertas-Cerdeira et al [ 45 ] experimentally studied the dynamic response of side-by-side inverted flags, with a transverse distance larger than double the length of the flag, demonstrating that the maximum angular amplitude is 36% higher than that of a single flag.…”

Section: Introductionmentioning

confidence: 99%

“…On the other hand, Huang et al [ 52 ] investigated the tandem configuration and found through numerical simulations that a destructive vortex merging reduces the flapping amplitude of the downstream inverted flag by 50% compared to a single flag. However, using an experimental approach, Hu et al [ 53 ] demonstrated that the downstream inverted flag can extract energy from the trailing edge vortex of the upstream flag at a critical flow velocity and a short streamwise distance, leading to increased angular amplitude of the downstream flag. This finding was found to be consistent with the behavior of tandem conventional flags observed by Jia and Yin [ 54 ] and Ristroph and Zhang [ 55 ].…”

Section: Introductionmentioning

confidence: 99%

“…To the best of the authors' knowledge, there has not been an in-depth study into multiple flags arranged side-by-side on the same pole, hence creating the motivation for this work. Our aim is, therefore, to study the coupling interaction between inverted flags in a Recently, the concurrent operation of two or more inverted flags has started to gain attention, with two main configurations being considered: side-by-side (see Figure 1b) [45][46][47][48][49][50][51] and tandem (see Figure 1b) [51][52][53] configurations within the horizontal plane. Huertas-Cerdeira et al [45] experimentally studied the dynamic response of sideby-side inverted flags, with a transverse distance larger than double the length of the flag, demonstrating that the maximum angular amplitude is 36% higher than that of a single flag.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Wind Energy Harvesting with Vertically Aligned Piezoelectric Inverted Flags

Yang,

Cioncolini,

Revell

et al. 2023

Sensors

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Wind-energy-harvesting generators based on inverted flag architecture are an attractive option to replace batteries in low-power wireless electronic devices and deploy-and-forget distributed sensors. This study examines two important aspects that have been overlooked in previous research: the interaction between an inverted flag and a neighboring solid boundary and the interaction among multiple contiguous inverted flags arranged in a vertical row. Systematic tests have been carried out with metal-only ‘baseline’ flags as well as a ‘harvester’ variant, i.e., the baseline metal flag covered with PVDF (polyvinylidene difluoride) piezoelectric polymer elements. In each case, dynamic response and power generation were measured and assessed. For baseline metal flags, the same qualitative trend is observed when the flag approaches an obstacle, whether this is a wall or another flag. As the gap distance reduces, the wind speed range at which flapping occurs gradually shrinks and shifts towards lower velocities. The increased damping introduced by attaching PVDF elements to the baseline metal flags led to a considerable narrowing of the flapping wind speed range, and the wall-to-flag or flag-to-flag interaction led to a power reduction of up to one order of magnitude compared to single flags. The present findings highlight the strong dependence of the power output on the flapping frequency, which decreases when the flag approaches a wall or other flags mounted onto the same pole. Minimum flag-to-flag and flag-to-wall spacing values are suggested for practical applications to avoid power reduction in multi-flag arrangements (2-3H and 1-2H respectively, where H is flag height).

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Wind Energy Harvesting with Vertically Aligned Piezoelectric Inverted Flags

Yang,

Cioncolini,

Revell

et al. 2023

Sensors

View full text Add to dashboard Cite

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“…The four-wings model or Model B (Figures 1b 2b 3b) exploits an wing-wing interaction phenomenon named 'clap-and-peel' for generating thrust. There has been a surge of interest in the recent years to study the interaction of multiple bodies in a fluid flow [25] [26] [27]. Deb et al(2020) [26] observed in-phase and out-of-phase oscillations in a couple of rigid plates which are oriented one beside another, through wind tunnel experiments.…”

Section: Introductionmentioning

confidence: 99%

Thrust Enhancement and Degradation Mechanisms due to Self-Induced Vibrations in Bio-inspired Flying Robots

Deb¹,

Huang²,

Verma³

et al. 2023

Preprint

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Bio-inspired flying robot (BIFR) which flies by flapping their wings experience continuously oscillating aerodynamic forces. These oscillations in the driving force cause vibrations in the motion of the body around the mean trajectory. That is, a BIFR hovering in place is not exactly stationary in space, rather it is oscillating in almost all directions about the hovering point in space. These oscillations affect the aerodynamic performance of the flier. Assessing the effect of these oscillations on particularly thrust generation in two-wings and four-wings BIFRs is the main objective of this work. To achieve such a goal two experimental setups were considered to measure the average thrust for the two BIFRs. The average thrust is measured over the flapping cycle of the BIFR. In the first experimental setup, the BIFR is installed at the end of a pendulum rod, in place of the pendulum mass. While flapping, the model creates a thrust force which raises the model along the circular trajectory of the pendulum mass to a certain angular position, which is an equilibrium point and it is also stable. Measuring the weight of the BIFR and the equilibrium angle it obtains, it is straightforward to estimate the average thrust by moment balance about the pendulum hinge. This pendulum setup allows the BIFR model to freely oscillate back and forth along the circular trajectory about the equilibrium position. As such, the estimated average thrust includes the effects of these self-induced vibrations. In contrast, we use another setup that relies on a load cell to measure thrust where the model is completely fixed. The thrust measurement of both the BIFRs using the above mentioned setups exhibited an interesting trend. The load cell or the fixed test lead to a higher thrust than the pendulum or the oscillatory test for the two-wings model, showing an opposite behavior for the four-wings model. That is self induced vibration have different effects on the two BIFR models. Note that the aerodynamic mechanisms of thrust generation for two-wings and four-wings are fundamentally different. A two-wings BIFR generates thrust through traditional flapping mechanisms whereas a four-wings model enjoys clapping effect and wing-wing interaction. In the present work, we use motion capture system, aerodynamic modeling and flow visualization to study the underlying physics of the observed different behaviors of the two flapping models.

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“…1 b, 2 b, 3 b) exploits a wing-wing interaction phenomenon named ’clap-and-peel’ for generating thrust. There has been a surge of interest in recent years to study the interaction of multiple bodies in a fluid flow 27 – 29 . Deb et al 28 observed in-phase and out-of-phase oscillations in a couple of rigid plates which are oriented one beside the other, through wind tunnel experiments.…”

Section: Introductionmentioning

confidence: 99%

Thrust enhancement and degradation mechanisms due to self-induced vibrations in bio-inspired flying robots

Deb,

Huang,

Verma

et al. 2023

Sci Rep

View full text Add to dashboard Cite

Bio-inspired flying robots (BIFRs) which fly by flapping their wings experience continuously oscillating aerodynamic forces. These oscillations in the driving force cause vibrations in the motion of the body around the mean trajectory. In other words, a hovering BIFR does not remain fixed in space; instead, it undergoes oscillatory motion in almost all directions around the stationary point. These oscillations affect the aerodynamic performance of the flier. Assessing the effect of these oscillations, particularly on thrust generation in two-winged and four-winged BIFRs, is the main objective of this work. To achieve such a goal, two experimental setups were considered to measure the average thrust for the two BIFRs. The average thrust is measured over the flapping cycle of the BIFRs. In the first experimental setup, the BIFR is installed at the end of a pendulum rod, in place of the pendulum mass. While flapping, the model creates a thrust force that raises the model along the circular trajectory of the pendulum mass to a certain angular position, which is an equilibrium point and is also stable. Measuring the weight of the BIFR and the equilibrium angle it obtains, it is straightforward to estimate the average thrust, by moment balance about the pendulum hinge. This pendulum setup allows the BIFR model to freely oscillate back and forth along the circular trajectory about the equilibrium position. As such, the estimated average thrust includes the effects of these self-induced vibrations. In contrast, we use another setup with a load cell to measure thrust where the model is completely fixed. The thrust measurement revealed that the load cell or the fixed test leads to a higher thrust than the pendulum or the oscillatory test for the two-winged model, showing the opposite behavior for the four-winged model. That is, self-induced vibrations have different effects on the two BIFR models. We felt that this observation is worth further investigation. It is important to mention that aerodynamic mechanisms for thrust generation in the two and four-winged models are different. A two-winged BIFR generates thrust through traditional flapping mechanisms whereas a four-winged model enjoys a clapping effect, which results from wing-wing interaction. In the present work, we use a motion capture system, aerodynamic modeling, and flow visualization to study the underlying physics of the observed different behaviors of the two flapping models. The study revealed that the interaction of the vortices with the flapping wing robots may play a role in the observed aerodynamic behavior of the two BIFRs.

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Flow-structure interactions of two tandem inverted flags in a water tunnel

Cited by 9 publications

References 35 publications

Wind Energy Harvesting with Vertically Aligned Piezoelectric Inverted Flags

Wind Energy Harvesting with Vertically Aligned Piezoelectric Inverted Flags

Thrust Enhancement and Degradation Mechanisms due to Self-Induced Vibrations in Bio-inspired Flying Robots

Thrust enhancement and degradation mechanisms due to self-induced vibrations in bio-inspired flying robots

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