21. Wake-induced response of vibro-impacting systems

Rohit Chawla, Aasifa Rounak, Chandan Bose, Vikram Pakrashi

https://doi.org/10.1063/5.0236147

The effects of a rigid barrier on the stability of the structure while it is undergoing phase-locked motions due to the surrounding fluid–structure interactions, are studied. The primary structure and the near wake dynamics are modeled as a harmonic oscillator and a Van der Pol oscillator, respectively, and are weakly coupled via acceleration coupling. Qualitative changes in the dynamical behavior of this system are investigated in the context of discontinuity-induced bifurcations that result from the interaction of fluid flow and nonsmoothness from the impact of the primary structure. Phenomenological behaviors like the co-existence of attractors and period-adding cascades of limit cycles separated by chaotic orbits are observed. The behavior of orbits in the local neighborhood of the discontinuity boundary is defined using a higher-order transverse discontinuity map, and the corresponding stability analysis is carried out using Floquet theory. The derived mapping is implemented to obtain the respective Lyapunov exponents. Results obtained using the mapping are demonstrated to accurately predict both the stable and chaotic regimes, as observed from the corresponding numerical bifurcation diagrams.

20. Effect of sweep angle on three-dimensional vortex dynamics over plunging wings

Alex Cavanagh, Chandan Bose , Kiran Ramesh

https://doi.org/10.1063/5.0227012

The effects of sweep angle and reduced frequency on the leading-edge vortex (LEV) structure over flapping swept wings in the Reynolds number (Re) range of O(10^4) are yet to be completely understood. With increasing interest in designing bio-inspired micro-air-vehicles, understanding LEV dynamics in such scenarios is imperative. This study investigates the effects of three different sweep angles (Λ = 0° 30°, and 60°) on LEV dynamics through high-fidelity improved delayed detached eddy simulation to analyze the underlying flow physics. Plunge ramp kinematics at two different reduced frequencies (k = 0.05 and 0.4) are studied to investigate the unsteady motion effects on LEV characteristics. The leading-edge suction parameter concept is applied to determine LEV initiation, and the results are verified against flow field visualization for swept-wing geometries. The force partitioning method is used to investigate the spanwise lift distribution resulting from the LEV. Distinct peaks in the lift coefficient occur for the high reduced frequency case due to the impulse-like plunging acceleration. This causes the LEV to detach from the leading edge more quickly and convect faster, significantly affecting the lift generated by the wing. As reduced frequency increases, the LEV breakdown mechanism switches from vortex bursting to LEV leg-induced instabilities. These results provide insights into the complex vortex structures surrounding swept wings at Re = 20000, and the impact both sweep angle and reduced frequency have on the lift contribution of these flow features

19. Effect of a fixed downstream cylinder on the flow-induced vibration of an elastically supported primary cylinder

Junlei Wang, Shenfang Li, Daniil Yurchenko, Hongjun Zhu, Chandan Bose

https://doi.org/10.1063/5.0207136

This paper numerically investigates the influence of a fixed downstream control cylinder on the flow-induced vibration of an elastically supported primary cylinder. These two cylinders are situated in a tandem arrangement with small dimensionless center-to-center spacing (L/D, L is the intermediate spacing and D is the cylinder diameter). The present two-dimensional (2D) simulations are carried out in the low Reynolds number (Re) regime. The primary focus of this study is to reveal the underlying flow physics behind the transition from vortex-induced vibration to galloping in the response of the primary cylinder due to the presence of another fixed downstream cylinder. Two distinct flow field regimes, namely, steady flow and alternate attachment regimes, are observed for different L/D and Re values. Depending on the evolution of the near-field flow structures, four different wake patterns, “2S,” “2P,” “2C,” and “aperiodic,” are observed. The corresponding vibration response of the upstream cylinder is characterized as interference galloping and extended vortex-induced vibration. As the L/D ratio increases, the lift enhancement due to flow-induced vibration is seen to be weakened. The detailed correlation between the force generation and the near-wake interactions is investigated. The present findings will augment our understanding of vibration reduction or flow-induced energy harvesting of tandem cylindrical structures.

18. Controlling the chaotic wake of a flapping foil by tuning its chordwise flexibility

Chhote Lal Shah, Dipanjan Majumdar, Chandan Bose , Sunetra Sarkar

https://doi.org/10.1016/j.jfluidstructs.2024.104134

Effects of chord-wise flexibility as an instrument to control chaotic transitions in the wake of a flexible flapping foil have been studied here using an immersed boundary method-based in-house fluid–structure-interaction solver. The ability of the flapping foil at an optimum level of flexibility to inhibit chaotic transition, otherwise encountered in a similar but rigid configuration, has been highlighted. The rigid foil manifests chaotic transition through a quasi-periodic-intermittency route at high dynamic plunge velocities; whereas, increasing the level of flexibility gradually regularises the aperiodic behaviour through a variety of interesting wake patterns. If flexibility is increased beyond an optimum level, aperiodicity sets in again and robust chaos is restored at very high flexibility levels. The mechanisms of triggering the order-to-chaos transition are different between the rigid and the high flexibility cases. Along the route to order and back to chaos, the flexible foil exhibits different flow-field behaviours, including far-wake switching, primary & secondary vortex streets, bifurcated wakes and interactive vortices between the bifurcated wakes. The underlying interaction mechanisms of the flow-field vortices responsible for the associated dynamical signatures of the wake have been closely tracked. This study further examines the optimum propulsive performance range of the flexible flapper and investigates its connection with the periodicity/regularity of the system.

17. Passive Suppression of Vortex-Induced Vibrations Using a Nonlinear Energy Sink - Numerical and Analytical Perspective

Abraham Thomas Chirathalattu*; Santhosh B; Chandan Bose , Rony Philip; Bipin Balaram

https://doi.org/10.1016/j.ymssp.2022.109556

This study investigates the suppression mechanism of instabilities induced by fluid-structure interactions (FSI) using passive vibration absorption devices, such as nonlinear energy sink (NES). The present FSI framework comprises a low-order phe- nomenological model, wherein the wake effect is modelled using the classical Van der Pol oscillator. The structure is represented as a cylindrical bluff body with degree-of- freedom along the cross-flow direction. The response of the NES-augmented struc- ture exhibits specific relaxation type oscillations, referred to as strongly modulated response (SMR), passively suppressing the high amplitude vortex-induced vibrations (VIV). The underlying mechanism of SMR is studied using an analytical approach based on the Complexification-Averaging (CXA) technique.

16. Chordwise flexible aft-tail suppresses jet-switching by reinstating wake periodicity in a flapping foil

Chhote Lal Shah, Dipanjan Majumdar, Chandan Bose , Sunetra Sarkar

https://doi.org/10.1017/jfm.2022.591

The effect of a chordwise flexible aft-tail of a rigid heaving aerofoil on the dynamical transitions of the trailing-wake is studied here. The two-way coupled fluid–solid dynamics is simulated using an in-house fluid–structure interaction (FSI) platform, comprising a discrete forcing immersed boundary method based incompressible Navier–Stokes solver, weakly coupled with a finite difference method based structural solver. The FSI dynamics is studied in comparison to the corresponding rigid tail configuration. For the latter, mild jet-switching due to quasi-periodic movement of the wake vortices gives way to vigorous jet-switching as the dynamics transitions to a state of intermittency, where the quasi-periodic behaviour gets interspersed with chaotic windows. Introduction of a moderately flexible tail regularises this intermittent dynamics, eliminating jet-switching. The wake exhibits a deflected reverse Kármán pattern with fluctuating angles, governed by quasi-periodicity. With a highly flexible tail (very low rigidity), the wake shows almost a symmetric reverse Kármán street as periodicity is restored. Flexibility of the aft-tail is next controlled by changing its length, and flow is regularised and periodicity retained for moderate rigidity for increased length. Different dynamical states are established through robust nonlinear dynamical tools. The underlying flow-field behaviour, instrumental in suppressing the jet-switching phenomenon, is identified through a detailed investigation of the near-field vortex interactions dictated by the dynamics. A suite of measures has also been derived from the unsteady flow field to quantify the interactions of the key near-field vortices with a view to understanding the mechanism of switching and its subsequent suppression through flexibility.

15. Transition boundaries and an order-to-chaos map for the flow-field past a flapping foil

Dipanjan Majumdar, Chandan Bose , Sunetra Sarkar

https://doi.org/10.1017/jfm.2022.385

The present study focuses on identifying the dynamical transition boundaries and presents an order-to-chaos map for the unsteady flow-field of a flapping foil in the low Reynolds number regime. Two new non-dimensional measures - maximum effective angle-of-attack and a leading-edge amplitude-based Strouhal number are proposed here, which can capture the physical effect of the parametric variations on the wake dynamics. The study also proposes generalised transition boundaries and an order-to-chaos map through a transitional regime in terms of these two newly proposed parameters.

14. Numerical investigation of discontinuity-induced bifurcations in an aeroelastic system with coupled non-smooth nonlinearities

Sai Vishal Gali*, Ashwad Raaj*, Chandan Bose , Venkatramani Jagadish, Grigorios Dimitriadis

https://link.springer.com/article/10.1007/s11071-022-07352-3

The present study focuses on investigating the bifurcation characteristics of a pitch-plunge aeroelastic system possessing coupled non-smooth nonlinearities, both in structural and aerodynamic fronts. At low airspeeds, the dynamical transitions occur predominantly due to the structural freeplay nonlinearity while the flow remains attached to the surface of the wing. However, beyond a critical value of airspeed, the system response is dominated by high amplitude pitch-dominated limit-cycle oscillations, which can be attributed to stall flutter. It is demonstrated that the freeplay gap plays a key role in combining the effects of structural and aerodynamic nonlinearities. At higher values of the freeplay gap, interesting discontinuity-induced bifurcation scenarios, such as grazing and boundary equilibrium bifurcations arise due to coupled nonlinear interactions, which can significantly impact the safety of the aeroelastic system.

13. Experimental Investigation on the Synchronization Characteristics of a Pitch-Plunge Aeroelastic System Exhibiting Stall Flutter

Dheeraj Tripathi*, R. Shreenivas*, Chandan Bose , Sirshendu Mondal, J Venkatramani

https://doi.org/10.1063/5.0096213

This study focuses on characterizing the bifurcation scenario and the underlying synchrony behaviour in a nonlinear aeroelastic system under deterministic as well as stochastic inflow conditions. Wind tunnel experiments arecarried out for a canonical pitch-plunge aeroelastic system subjected to dynamic stall conditions. We observe intermittent phase synchronization between pitch and plunge modes near the fold point; whereas, synchronization via phase trappingis observed near the Hopf point. Repeating the experiments under stochastic inflow conditions, we observe two different aeroelastic responses; low amplitude noise-induced random oscillations (NIROs) and high amplitude random LCOs (RLCOs) during stall flutter. The present study shows asynchrony between pitch and plunge modesin the NIRO regime. At the onset of RLCOs, asynchrony persists even though the relative phase distribution changes. With the further increase in flow velocity, we observe intermittent phase synchronization in the flutter regime.

12. Stall-induced fatigue damage analysis of nonlinear aeroelastic systems subjected to randomly fluctuating inflow

Dheeraj Tripathi*, Sai Vishal*, Chandan Bose , J Venkatramani

https://doi.org/10.1016/j.ijnonlinmec.2022.104003

This study focuses on characterizing the fatigue damage accumulated in nonlinear aeroelastic systems subjected to stochastic input flows. The response dynamics and the associated fatigue damage of the aeroelastic system, possessing different sources of nonlinearities, are systematically investigated under isolated cases of deterministic and stochastic input flows. It is observed that different time scales and intensities of the oncoming flow fluctuation play a pivotal role in dictating the fatigue damage in aeroelastic systems. Fatigue damage is observed to be significantly higher for torsionally dominant oscillations in the dynamical stall regime compared to the oscillations at the attached flow regime.

11. Routes to Synchronization in a pitch-plunge aeroelastic system with coupled structural and aerodynamic nonlinearities

Sai Vishal Gali*, Ashwad Raaj*, Chandan Bose , Venkatramani Jagadish

https://doi.org/10.1016/j.ijnonlinmec.2021.103766

In this study, we investigate the response characteristics of a pitch-plunge aeroelastic system possessing coupled non-smooth nonlinearities, namely free-play in the structure and dynamic stall in the flow. We demonstrate the need to present a one-one relationship between the dynamic stall behavior with respect to the output aeroelastic response. We systematically demonstrate the different routes to synchronization in the nonlinear aeroelastic problem and use the same to heuristically demarcate coupled mode flutter against stall flutter.

10. Enhancing Piezoelectric Energy Harvesting from the Flow-Induced Vibration of a Circular Cylinder Using Dual Splitters

Junlei Wang; Shanghao Gu; Abdessattar Abdelkefi; Chandan Bose

https://doi.org/10.1088/1361-665X/abefb5

This study is focused on enhancing the piezoelectric energy harvesting from the flow-induced vibration of a circular cylinder by using two symmetric splitters in different relative angular positions with respect to the oncoming uniform flow. Both wind tunnel experiments and numerical simulations are carried out to study the effect of different installation angles of the dual splitters on the energy harvesting efficiency with the increasing flow velocity. This study systematically carries out the performance analysis of the vortex-induced vibration-based energy harvester with multiple splitters and directly contributes to the optimized design of an innovative wind energy harvester.

9. Dynamic interlinking between near and far-field wakes behind a pitching-plunging airfoil

Chandan Bose ; Sayan Gupta; Sunetra Sarkar

https://doi.org/10.1063/5.0024084

This study establishes a dynamic link between the near and far-field wake transitions and investigates the role of aperiodic jet-switching in ushering in chaos in the wake of a pitch-plunge flapping system. The mechanism of jet-switching and the role of leading-edge vortex are also revealed in this paper.

8. Effect of gusty inflow on the jet-switching characteristics of a plunging foil

Dipanjan Majumdar; Chandan Bose ; Sunetra Sarkar

https://doi.org/10.1063/5.0024084

This study investigates the effect of stochastic inflow fluctuations on the jet-switching characteristics of a harmonically plunging elliptic foil, in comparison to steady- uniform inflow, at a low Reynolds number regime. Numerical simulations are performed with an Immersed Boundary Method (IBM)-based in-house flow solver and the temporal inflow fluctuations are generated by an Ornstein-Uhlenbeck process - a stationary Gauss- Markov process with a chosen correlation function.

7. Capturing the Dynamical Transitions in the Flow-field of a Flapping Foil using Immersed Boundary Method

Dipanjan Majumdar; Chandan Bose ; Sunetra Sarkar

https://doi.org/10.1016/j.jfluidstructs.2020.102999

This study explores the scope of body non-conformal mesh methods in comparison to body-fitted approaches in capturing complex flow topologies, especially, during aperiodic transition in the unsteady flow-field of a flapping foil.

6. Transition to chaos in the flow-induced vibration of a pitching-plunging airfoil at low Reynolds numbers : Ruelle-Takens-Newhouse scenario

Chandan Bose ; Sayan Gupta; Sunetra Sarkar

DOI: 10.1016/j.ijnonlinmec.2018.11.012

This study reports a Ruelle-Takens-Newhouse quasi-periodic route during the transition from periodic to chaotic dynamics in the fluid-elastic response of a 2-dof flexibly-mounted airfoil with very low solid-to-fluid added mass ratio through robust nonlinear dynamic analysis.

5. Investigating chaotic wake dynamics past a flapping airfoil and the role of vortex interactions behind the chaotic transition

Chandan Bose ; Sunetra Sarkar

DOI: 10.1063/1.5019442

This study revealed that slightly erratic leading edge separation could trigger a complete chaotic breakdown of the wake of a flapping wing that mimics natural flyers like birds and insects. Fundamental vortex interaction mechanism that sustains chaos in the wake have also been identified in the study.

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4. Dynamical behaviour of unsteady flow-field of an elastically mounted flapping airfoil

Chandan Bose ; Sayan Gupta; Sunetra Sarkar

DOI: 10.2514/1.J056664

The present study reports the quasi-periodic flow dynamics behind a spanwise flexible flapping airfoil. In the qualitative transition in the unsteady flowfield, the trailing-edge wake loses its periodicity beyond a critical wind velocity and becomes quasi-periodic (QP) in nature at a regime of comparable solid and fluid added mass (μ = 5). The correlation coefficient of the vorticity field and the reconstructed phase space, frequency spectra, Poincaré sections, and recurrence plots of the aerodynamic loads establish the presence of quasi-periodicity in the flow topology conclusively. The loss of periodicity is shown to lead to variability in the aerodynamic loads at the corresponding flow regimes, implying the potential requirement of feedback control mechanisms for stable operations at these flow regimes.

3. Transient and stable chaos in dipteran flight inspired flapping flight

Chandan Bose ; Vikas Reddy; Sayan Gupta; Sunetra Sarkar

DOI: 10.1115/1.4038447

This paper deals with the nonlinear fluid structure interaction (FSI) dynamics of a Dipteran flight motor inspired flapping system in an inviscid fluid. In the present study, the FSI effects are incorporated to an existing forced Duffing oscillator model to gain a clear understanding of the nonlinear dynamical behavior of the system in the presence of aerodynamic loads. The present FSI framework employs a potential flow solver to determine the aerodynamic loads. Interesting dynamical behavior including period doubling, chaotic transients, periodic windows, and finally an intermittent transition to stable chaotic attractor have been observed in the response with an increase in the bifurcation parameter.

2. Investigations on a vortex induced vibration based energy harvester

S Krishna Kumar; Chandan Bose ; Shaikh Faruque Ali; Sayan Gupta; Sunetra Sarkar

DOI: 10.1063/1.5001863

This study investigates energy harvesting from vortex induced vibrations of a flexible cantilevered flapper placed in the wake of a rigid circular cylinder. The effect of the gap between the cylinder and the flapper on the energy harvested is investigated through wind tunnel experiments and numerical simulations. As the flow speed is varied, a transition in the flapper dynamics is observed, which in turn affects the power extracted by the harvester. Numerical investigations reveal that the flapper dynamics is different depending on whether the vortices are shed ahead or behind the flapper. This study concludes that the choice of the gap influences the energy harvesting potential of such harvesters.

1. Identifying the route to chaos in the flow past a flapping airfoil

Sandeep Badrinath; Chandan Bose; Sunetra Sarkar

DOI: 10.1016/j.euromechflu.2017.05.012

This paper focuses on analyzing the dynamics and identifying the route to chaos in the wake of a plunging airfoil. The intermittency route to chaos is conclusively established using techniques from time series analysis, such as phase space reconstruction and recurrence plots. A qualitative analysis of the patterns in the recurrence plots is used to identify the type of intermittency to be Type I. Moreover, the implication of Type I intermittency into the flow dynamics has been studied through various vortex interaction mechanisms and its effect on the thrust generation.