Flexible Fin Research Articles

Analysis of power law fluid-structure interaction in an open trapezoidal cavity

The present paper investigates the mixed convection heat transfer of non-Newtonian fluid-structure interaction (FSI) inside an open trapezoidal cavity. The base of the cavity is fixed at constant temperature while the other walls are adiabatic. The flow passes over the open side of the cavity through a parallel-plate channel. An elastic fin is dangled from the top wall of the channel and stand facing the open cavity. The current model presents a two- dimensional incompressible laminar flow and unsteady-state conditions using the non-Newtonian power- law fluids. Numerical simulation is achieved using finite element method with arbitrary Lagrangian–Eulerian (ALE) scheme. The effects of Cauchy number, Reynolds number, Richardson number and the index of power law fluid are examined with ranges of (Ca = 10−20–10−3, Re = 100–300, Ri = 0.01–10 and n = 0.5–1.5). The results show that at Re = 300, Nusselt number of a stiff fin is 2.6% and 7% higher than that of softer flexible fin for n = 0.5 and 1.5, respectively. For low Ri number, shear-thickening fluid manifests higher Nusselt number while for high Ri number, the shear-thinning fluid has the higher values. It is found also that the fluttering phenomenon of the fin takes place at the highest Ri and Re numbers with shear-thinning fluid and Newtonian fluid as well.

Computational investigation on a self-propelled pufferfish driven by multiple fins

Based on experimental measurements of a live fish, a numerical model is established for a pufferfish driven by the locomotion of its multiple flexible fins. The self-propelled motion of the fish is investigated under unsteady swimming conditions, including the accelerating and subsequent quasi-steady stages, to analyse the motion mechanisms of a real fish model with multiple flexible fins. Present numerical approach combines Computational Fluid Dynamics (CFD) and Multi-Body Dynamics (MBD), which allows for the analysis of the interaction between fluid and a fish with multiple fins. Benefitting from the available experimental data of the live fish, the deformation of each fin surface can be prescribed, and we name this condition as flexible in this paper. To elucidate the impact of flexible fins on the propulsion performance of fish swimming, simulations are also performed for rigid fins with the same kinematic motion profiles imposed on the leading edge of fin surfaces. With the developed tool, unsteady hydrodynamic forces, vortex interaction between body and fins associated with MPF swimming mode are numerically predicted. The obtained results highlight the effect of flexibility of fins on thrust generation and efficiency improvement for fish undergoing free swimming.

Mixed convection heat transfer by nanofluids in a cavity with two oscillating flexible fins: A fluid–structure interaction approach

This study investigated the effects of two oscillating fins on the heat transfer rate and flow characteristics of a nanofluid inside a square enclosure. Both fins were attached to the hot wall and both fins oscillated at the same frequencies and amplitudes. The finite element method implemented in the arbitrary Lagrangian–Eulerian (ALE) technique was used to solve the equations describing the interactions and movements of the nanofluid and fins. Comparisons of our results and those reported in previous studies demonstrated that the modeling and numerical investigations were valid and reliable. The results showed that the increase in the heat transfer rate was due to the oscillation of the fins. In addition, the increasing trend in the heat transfer rate due to the oscillating fins decreased as the ratio of the thermal conductivity of the fins relative to the nanofluid increased. Increasing the thermal conductivity and viscosity parameters enhanced and weakened the heat transfer rate, respectively.

Theoretical and numerical studies on a five-ray flexible pectoral fin during labriform swimming

Natural fish have evolved with an excellent swimming performance after millions of years. Based on the flexible features of the pectoral fin, this paper focuses on the kinematics and hydrodynamics of the fin when fish are swimming stably in still water in labriform mode. The locomotion mechanism based on the morphology of the pectoral fin is applied to establish a kinematic model composed of five rays and membranes, which is adopted to control the pectoral fin to reach deformation in approximately the same way as the labriform mode. A semi-empirical theoretical model based on the kinematics is proposed to calculate the hydrodynamic force. In order to study the flow field, the numerical simulation of fluid–structure interaction is carried out and the results are validated by the present semi-empirical model, which also verifies the feasibility of the semi-empirical theoretical model for describing the dynamics of the pectoral fin under a complex water environment. In addition, the relationship between propulsion performance and locomotion parameters (e.g. frequency of motion, amplitude of flapping and rowing angle, and phase lag between flapping and rowing) of the multi-degree of freedom flexible pectoral fin is also revealed. It is found that the frequency and amplitude of the flapping angle have a significant influence on the hydrodynamic thrust, while the rowing angle and phase lag have little effect. The established models and the results provide effective tools and significant reference for the design of bionic pectoral fins.

Digging with ‘hands’: observations of food capture in the flying gurnard Dactylopterus volitans (Linnaeus, 1758)

ABSTRACT Videofilms of a foraging flying gurnard (Dactylopterus volitans) were collected at Itaipu, Niterói, RJ, Brazil. Analysis revealed details of the use of anterior parts of the pectoral fins which act as digging ‘hands’ to access infaunal prey items that are subsequently captured by oral suction feeding. Each pectoral fin has two distinct sections articulated separately on the pectoral girdle. The digging ‘anterior pectoral fin’ mainly consists of segmented and flexible fin rays but has an anterior robust unsegmented ray that provides an edge to the ‘hand’, allowing penetration of the substratum. The huge ‘posterior pectoral fins’ are supported by unsegmented rays. Most digging episodes involved one ‘hand’ and consisted of 1–7 cycles of movement with frequencies 1.15–3.74 cycles s−1. During a cycle, the ‘hand’ is moved forwards and medially above the substratum, then is twisted medially and simultaneously depressed so that the anterior unsegmented ray impacts and enters the substratum. The hand is then drawn backwards and laterally to disturb the substratum. To prevent upward pitching of the head during digging, the ‘posterior pectoral fins’ are both moved anteriorly and laterally to shift the centre of gravity forwards while the caudal and second dorsal fins continue to provide propulsive force.

A fluid–structure interaction solver for the study on a passively deformed fish fin with non-uniformly distributed stiffness

Research on fish locomotion has made extensive progress towards a better understanding of how fish control their flexible body and fin for propulsion and maneuvering. Although the biologically flexible fish fins are believed to be one of the most important features to achieve optimal swimming performance, due to the limitations of the existing numerical modeling tool, studies on a deformable fin with a non-uniformly distributed stiffness are rare. In this work, we present a fully coupled fluid–structure interaction solver which can cope with the dynamic interplay between flexible aquatic animal and the ambient medium. In this tool, the fluid is resolved by solving Navier–Stokes equations based on the finite volume method with a multi-block grid system. The solid dynamics is solved by a nonlinear finite element method. A sophisticated improved IQN-ILS coupling algorithm is employed to stabilize solution and accelerate convergence. To demonstrate the capability of the developed Fluid–Structure-Interaction solver, we investigated the effect of five different stiffness distributions on the propulsive performance of a caudal peduncle-fin model. It is shown that with a non-uniformly distributed stiffness along the surface of the caudal fin, we are able to replicate similar real fish fin deformation. Consistent with the experimental observations, our numerical results also indicate that the fin with a cupping stiffness profile generates the largest thrust and efficiency whereas a heterocercal flexible fin yields the least propulsion performance but has the best maneuverability.

Development and testing of the re-deployable radiator for deep space explorer

This paper reports the design, fabrication, and testing of a reversible thermal panel breadboard model (RTP-BBM). RTP is a flexible, re-deployable radiator that autonomously controls the temperature of a heat source. It promotes heat dissipation by deploying the radiator surface when the heat source is at a high temperature. Conversely, in a cold case, heat dissipation is conserved by stowing the radiator surface. Herein, deployment/stowing and thermal vacuum tests were conducted herein to evaluate the validity of the design, and model correlations were conducted via thermal analysis. The RTP-BBM comprises high thermal conductivity graphite sheets as the flexible fin, and shape-memory alloys (SMA) as a temperature sensitive passive actuator. The deployment/stowing test was conducted in a thermal constant bath, confirming that the fin was deployed and stowed according to the SMA temperature. However, temperature hysteresis of up to +60 °C was confirmed between heating and cooling cycles. In the thermal vacuum test, power step and power cycle tests were conducted. Results showed that the fin deployed and stowed according to the temperature of the onboard equipment while autonomously regulating the temperature. Additionally, the thermal analysis model correlated with the experimental results, showing good agreement within ±6 °C.

Dynamic Analysis of a Robotic Fish Propelled by Flexible Folding Pectoral Fins

SUMMARYBiological fish can create high forward swimming speed due to change of thrust/drag area of pectoral fins between power stroke and recovery stroke in rowing mode. In this paper, we proposed a novel type of folding pectoral fins for the fish robot, which provides a simple approach in generating effective thrust only through one degree of freedom of fin actuator. Its structure consists of two elemental fin panels for each pectoral fin that connects to a hinge base through the flexible joints. The Morison force model is adopted to discover the relationship of the dynamic interaction between fin panels and surrounding fluid. An experimental platform for the robot motion using the pectoral fin with different flexible joints was built to validate the proposed design. The results express that the performance of swimming velocity and turning radius of the robot are enhanced effectively. The forward swimming velocity can reach 0.231 m/s (0.58 BL/s) at the frequency near 0.75 Hz. By comparison, we found an accord between the proposed dynamic model and the experimental behavior of the robot. The attained results can be used to design controllers and optimize performances of the robot propelled by the folding pectoral fins.

Effect of Nonuniform Flexibility on Hydrodynamic Performance of Pitching Propulsors

Many aquatic animals propel themselves efficiently through the water by oscillating flexible fins. These fins are, however, not homogeneously flexible, but instead their flexural stiffness varies along their chord and span. Here, we develop a simple model of these functionally graded materials where the chordwise flexibility of the foil is modeled by one or two torsional springs along the chord line. The torsional spring structural model is then strongly coupled to a boundary element fluid model to simulate the fluid–structure interactions. We show that the effective flexibility of the combined fluid–structure system scales with the ratio of the added mass forces acting on the passive portion of the foil and the elastic forces defined by the torsional spring hinge. Importantly, by considering this new scaling of the effective flexibility, the propulsive performance is then detailed for a foil with a flexible hinge that is actively pitching about its leading edge. The scaling allows for the resonance frequency of the fluid–structure system and the bending pattern of the propulsor to be independently varied by altering the effective flexibility and the location of a single torsional spring along the chord, respectively. It is shown that increasing the flexion ratio, by moving the spring away from the leading edge, leads to enhanced propulsive efficiency, but compromises the thrust production. Proper combination of two flexible hinges, however, can result in a gain in both the thrust production and propulsive efficiency.

Side-swimming plankton snail flaps shell like a fin

Amy Maas, Ferhat Karakas and David Murphy never know what they're going to turn up when they go trawling for zooplankton. ‘We work on the swimming of various sea butterfly species’, says Murphy, adding that unlike true butterflies, sea butterflies are miniscule snails that live at depth and swim to the surface at night, propelled by minute wings like flying insects. But one day in September 2017, the trio was in for a surprise. In addition to their usual haul of sea butterflies, Karakas and Maas turned up a pair of tiny heteropod snails, Atlanta selvagensis. ‘I had never heard of heteropods before’, admits Murphy. As virtually nothing was known about these rare aquatic molluscs, the trio rushed them back to Murphy's high-tech zooplankton movie set in the lab, in the hope of catching them in the act of swimming.Describing the tank, Murphy says, ‘Our filming system consists of three synchronized high-speed cameras pointed at a tiny aquarium from three different directions’. Liberating the plankton into the tank, Karakas kept his fingers crossed that the heteropods would swim precisely through the centre of the three cameras’ field of view so that he could accurately reconstruct their movements in three dimensions. And, after staying up all night, his patience was rewarded when one of the minute snails flapped into view. But it wasn't waving its foot alone, like a miniature paddle; it was also moving its shell like an additional wing in time with the foot. ‘My mind was completely blown when Ferhat showed me the video’, says Murphy, as the shell had been thought to stabilise the mollusc like a ship's keel. ‘We … realised that the existing (very cursory) description of its swimming behaviour was completely different from what we had captured’.Painstakingly reconstructing their 3D trajectory, Murphy saw that the snails appeared to be swimming like birds that were flying on their sides, with the ‘wing’ structures meeting on the left and right of the animal. After closer inspection, he saw that the mollusc held the shell and foot fin together on one side of its body at the start of a wing beat and then peeled the front edges of the appendages apart before sweeping them above and below the body in an arc. Near the end of the first half of a wing beat (the power stroke), the snail curved the front edges of the foot fin and shell in toward each other, before snapping the rear edges of the structures together on the opposite side of its body. Then it repeated the whole process in reverse. In addition, the 2.2 mm long snails completed almost 10 wing beats per second and reached an impressive speed of 53.1 mm s−1 midway through the power-generating half of the wing beat. He also suspects that the swimming snails get two bangs for every wing-beat buck, generating a tiny region of spinning low-pressure above each flapping structure as they peel the wings apart at the beginning of both halves of the full wing beat to propel themselves through the water. However, the bulky shell is less manoeuvrable than the flexible foot fin, sweeping through 170 deg, in contrast to the fin, which sweeps over a colossal 220 deg. ‘We think that this is the largest stroke amplitude ever measured in the animal kingdom’, says Murphy.Having revealed the heteropod's unconventional mode of transport, Murphy and his colleagues are keen to go on more voyages of plankton discovery to learn how fluid flowing around the minute aquanauts propels them to the surface.

Physics of unsteady thrust and flow generation by a flexible surface flapping in the absence of a free stream

Inspired by the flexible wings and fins of flying and swimming animals, we investigate the flow induced by the interaction between a flapping flexible surface and the surrounding fluid for the limiting case of Strouhal numberSt→∞(zero free-stream speed). The model selected for this purpose is a two-dimensional sinusoidally pitching rigid symmetric foil to which is attached at the trailing edge a thin chordwise flexible surface (along the chord line). The flow so generated is a coherent jet aligned along the foil centreline, containing a reverse Bénard–Kármán vortex street and delivering a corresponding unidirectional thrust. We analyse the flow and thrust generation process. The measured velocity field suggests that the flow and thrust generation mainly occurs during the phases when the trailing edge is near the centreline. Flexibility of the surface is important in accelerating the near-wake flow and in transferring momentum and energy to the fluid. We present a detailed account of when and where the momentum and energy are added to the fluid. This study shows that the deformations of the flexible surface are responsible for generating a favourable pressure gradient along the jet direction, and for the observed unsteady actuator disc-type action.

Using spanwise flexibility of caudal fin to improve swimming performance for small fishlike robots

This paper examines the beneficial effects of the spanwise flexibility of the caudal fin for the improvement of the swimming performance for small fishlike robots. A virtual swimmer is adopted for controlled numerical experiments by varying the spanwise flexible trajectories and the spanwise flexible size of the caudal fin while keeping the body kinematics fixed. 3-D Navier-Stokes equations are used to compute the viscous flow over the robot. Elliptical, parabolic and hyperbola trajectories are chosen to describe the spanwise flexible profile of the caudal fin. According to the sign (positive or negative) of the phase difference of the swinging motion, the spanwise flexibility can be divided into the fin surface of “bow” and the fin surface of “scoop”. It is observed that for both the fin surface of “bow” and the fin surface of “scoop”, the spanwise elliptical trajectory has the optimal swimming velocity, thrust, lateral force, and efficiency. With comparisons, using the flexible caudal fin with the fin surface of “bow”, the lateral force and the power consumption can be reduced effectively and the swimming stability can be increased while reducing little the swimming velocity and thrust. Meanwhile, using the flexible caudal fin with the fin surface of “scoop” can greatly improve the swimming velocity, thrust, and efficiency while increasing part of the lateral force and the power consumption. Three-dimensional flow structures clearly indicate the evolution process around the swimming robot. It is suggested that the fish, the dolphin, and other aquatic animals may benefit their hydrodynamic performance by the spanwise flexibility of the caudal fin.

Forced convection heat transfer from a circular cylinder with a flexible fin

Forced convection heat transfer from a circular cylinder with a flexible fin in laminar flow with Re = 200 and Pr = 0.7 is investigated numerically. The two-dimensional incompressible Navier-Stokes equations and energy equation are coupled with the Euler-Bernoulli beam equation to describe the flow-induced vibration (FIV) of the flexible fin considering the convection heat transfer process. The modified characteristic-based split scheme, Galerkin finite element method, semi-torsional spring analogy method and loosely coupled partitioned approach are employed irrespectively for the flow and convection heat transfer, fin vibration, mesh movement and fluid–structure interaction. The accuracy and stability of the proposed numerical method are validated using three benchmark models including the forced convection heat transfer from a stationary cylinder, forced convection heat transfer from a transversely oscillating cylinder and FIV of a flexible plate behind a square cylinder. Finally, forced convection heat transfer characteristics from a circular cylinder with a flexible fin with fin length l = 0.5D–1.5D (D is the cylinder diameter) and elastic modulus E = 104 - 5 × 105 are analyzed in detail. The numerical results show that, when the vortex shedding frequency approaches the natural frequency of the flexible fin, the FIV frequency is locked on the natural frequency and the fin exhibits large-amplitude vibration. As a result, the ‘dead water’ region behind the cylinder is reduced and the convection heat transfer is improved. In the combinations of parameters considered, a maximum of 11.07% enhancement in heat transfer is obtained by the flexible fin.

Effect of flexural stiffness distribution of a fin on propulsion performance

Experimental investigations on biomimetic mechanical fins have been carried out by researchers to study and mimic the behaviour of fish. Flexible fins are proven to be better than rigid fins in terms of thrust force generation and efficiency when the degree of flexibility is chosen appropriately. It is observed that fishes can modulate their fin stiffness by muscle coactivation. Also, fins of different variety of fishes are developed with different stiffnesses through natural evolution to cope up with different living conditions. Inspired by the natural design of fish fins with varying flexural stiffness along the chord, in this work, a search-based numerical optimization study is conducted to investigate on the optimal flexural stiffness distribution yielding maximum thrust force. For this, a dynamic model of a flexible fin is developed through multi-body dynamics approach by considering the flexible fin as multiple rigid segments connected with torsion springs. Blade element method is utilized to compute the hydrodynamic forces acting on the fin segments. Based on the design optimizations several flat plate fins of trapezoidal geometry are developed with varied distribution of stiffness. Experiments are conducted with the fabricated fins to validate the optimization results for maximized propulsion performance.

Mechatronic Design and Manufacturing of the Intelligent Robotic Fish for Bio-Inspired Swimming Modes

This paper presents mechatronic design and manufacturing of a biomimetic Carangiform-type autonomous robotic fish prototype (i-RoF) with two-link propulsive tail mechanism. For the design procedure, a multi-link biomimetic approach, which uses the physical characteristics of a real carp fish as its size and structure, is adapted. Appropriate body rate is determined according to swimming modes and tail oscillations of the carp. The prototype is composed of three main parts: an anterior rigid body, two-link propulsive tail mechanism, and flexible caudal fin. Prototype parts are produced with 3D-printing technology. In order to mimic fish-like robust swimming gaits, a biomimetic locomotion control structure based on Central Pattern Generator (CPG) is proposed. The designed unidirectional chained CPG network is inspired by the neural spinal cord of Lamprey, and it generates stable rhythmic oscillatory patterns. Also, a Center of Gravity (CoG) control mechanism is designed and located in the anterior rigid body to ensure three-dimensional swimming ability. With the help of this design, the characteristics of the robotic fish are performed with forward, turning, up-down and autonomous swimming motions in the experimental pool. Maximum forward speed of the robotic fish can reach 0.8516 BLs-1 and excellent three-dimensional swimming performance is obtained.

Passive locomotion of freely movable flexible fins near the ground

We numerically examine the hydrodynamic interaction between a flexible fin and surrounding fluid near the ground when four relevant parameters of initial position, bending rigidity, mass ratio and Reynolds number are varied. The leading edge of the fin is fixed in the streamwise direction, whereas the lateral motion is freely movable by the fluid–flexible body interaction near the ground. When the fin is initially positioned far from the ground, the fin passively migrates toward another wall-normal position near the ground for an equilibrium state due to larger positive deflection angle for the fin than the negative angle by the effects of vorticity generated by the lateral velocity gradient near the ground. In addition, as the flapping amplitude of the fin is small for large bending rigidity and small mass ratio, the great asymmetry between the positive and negative deflection angles reduces the transient time of the fin to reach the equilibrium position near the ground, and thus the fins can quickly take the hydrodynamic benefits with low drag at an equilibrium state without any energy consumption for lift force due to local balance between the flapping motion and the ground. The most important observation is that the equilibrium position of the fin is invariant to the initial position, bending rigidity and mass ratio of the fin. However, the equilibrium position of the fin is dramatically affected by the Reynolds number. The present results provide new insights into the functional role of the relevant parameters in passively flapping-based locomotion near the ground.

A multi-body dynamics based numerical modelling tool for solving aquatic biomimetic problems

In this paper, a versatile multi-body dynamic algorithm is developed to integrate an incompressible fluid flow with a bio-inspired multibody dynamic system. Of particular interest to the biomimetic application, the algorithm is developed via four properly selected benchmark verifications. The present tool has shown its powerful capability for solving a variety of biomechanics fish swimming problems, including self-propelled multiple degrees of freedom with a rigid undulatory body, multiple deformable fins and an integrated system with both undulatory fish body and flexible fins. The established tool has paved the way for future investigation on more complex bio-inspired robots and live fish, for either propulsion or manoeuvring purposes.

The evolution of underwater flight: The redistribution of pectoral fin rays, in manta rays and their relatives (Myliobatidae)

Batoids are a diverse clade of flat cartilaginous fishes that occur primarily in benthic marine habitats. The skates and rays typically use their flexible pectoral fins for feeding and propulsion via undulatory swimming. However, two groups of rays have adopted a pelagic or bentho-pelagic lifestyle and utilize oscillatory swimming-the Myliobatidae and Gymnuridae. The myliobatids have evolved cephalic lobes, anteriorly extended appendages that are optimized for feeding, while their pectoral fins exhibit several modifications that likely arose in association with functional optimization of pelagic cruising via oscillatory flight. Here, we examine variation in fin ray distribution and ontogenetic timing of fin ray development in batoid pectoral fins in an evolutionary context using the following methods: radiography, computed tomography, dissections, and cleared and stained specimens. We propose an index for characterizing variation in the distribution of pectoral fin rays. While undulatory swimmers exhibit symmetry or slight anterior bias, we found a posterior shift in the distribution of fin rays that arose in two distinct lineages in association with oscillatory swimming. Undulatory and oscillatory swimmers occupy nonoverlapping morphospace with respect to fin ray distribution illustrating significant remodeling of pectoral fins in oscillatory swimmers. Further, we describe a derived skeletal feature in anterior pectoral fins of the Myliobatidae that is likely associated with optimization of oscillatory swimming. By examining the distribution of fin rays with clearly defined articulation points, we were able to infer evolutionary trends and body plan remodeling associated with invasion of the pelagic environment. Finally, we found that the number and distribution of fin rays is set early in development in the little skate, round stingray, and cownose ray, suggesting that fin ray counts from specimens after birth or hatching are representative of adults and therefore comparable among species.

Hydrodynamics of flexible fins propelled in tandem, diagonal, triangular and diamond configurations

A fish may gain hydrodynamic benefits from being a member of a school. Inspired by fish schools, a two-dimensional simulation was performed for flexible fins propelled in tandem, diagonal, triangular and diamond configurations. The flow-mediated interactions between the flexible fins were analysed by using an immersed boundary method. A transverse heaving motion was prescribed on the leading edge of each fin, and other posterior parts passively adapted to the surrounding fluid as a result of the fluid–flexible-body interaction. The flexible fins were allowed to actively adjust their relative positions in the horizontal direction. The four basic stable configurations are spontaneously formed and self-sustained purely by the vortex–vortex and vortex–body interactions. The hydrodynamic benefits depend greatly on the local positions of the members. For the same heaving motion prescribed on the leading edge, the input power of the following fin in the stable tandem and diagonal configurations is lower by 14 % and 6 %, respectively, than that of the leading fin. The following fin in the diagonal formation can keep pace with the leading fin even for reduced heaving amplitudes because of the help of the leader via their shared fluid environment, where its required input power is reduced by 21 %. The heaving amplitudes of the trailing fins are reduced to optimize the propulsive efficiency, and the average efficiencies in the triangular and diamond configurations increase by up to 14 % and 19 %, respectively, over that of the isolated swimmer. The propulsive efficiencies are enhanced by 22 % for the fins in the second row and by 36 % for the fin in the third row by decreasing the heaving amplitude in the diamond formation.

MHD mixed convection in a nanofluid filled vertical lid-driven cavity having a flexible fin attached to its upper wall

In this study, fluid flow and heat transfer in a vertical lid-driven CuO–water nanofluid filled square cavity with a flexible fin attached to its upper wall under the influence of an inclined magnetic field are numerically investigated. The left vertical wall of the cavity is colder than right vertical wall, and it moves in + y direction with constant speed. Horizontal walls of the cavity are insulated. The governing equations are solved with finite element method. The arbitrary Lagrangian–Eulerian method is used to describe the fluid motion within the cavity for the flexible fin in the fluid-structure interaction model. The influence of Richardson number (between 0.01 and 100), Hartmann number (between 0 and 50), inclination angle of the magnetic field (between 0 and 90%), nanoparticle volume fraction (between 0 and 0.05) and Young’s modulus of flexible fin (between 250 and 5000) on the flow and heat transfer were numerically studied. It is observed that the presence of the elastic fin affects the flow field and thermal characteristics of the cavity. The local and average heat transfer enhance as the Richardson number, solid volume fraction of the nanoparticle increase whereas deteriorate as the value of the Hartmann number and inclination angle of the magnetic field increases due to the dampening of the fluid motion with Lorentz forces. The addition of the nanoparticles is more effective along the lower part of the right vertical wall where the heat transfer process is effective. The average heat transfer increases by 28.96% for solid volume fraction of 0.05% compared to base fluid when the flexible fin is attached to the upper wall. The average heat transfer deteriorates by 10.10% for cavity with and without fin at Hartmann number of 50 compared to the case without magnetic field. The average heat transfer enhances as the Young’s modulus of the flexible fin decreases and the average Nusselt number increases by 13.24% for Young’s modulus of 250 compared to configuration for the cavity having the Young’s modulus of 5000.