Flow-induced Vibration Phenomenon Research Articles

Numerical investigation on flow-induced vibration of porous square cylinder and its mechanism research

Focusing on the porous square cylinder model, we employ numerical investigation to explore flow-induced vibration phenomena, influencing factors, and associated mechanisms. Initially, we provide a brief overview of the current research status regarding flow-induced vibration in porous media. Subsequently, we establish a porous square cylinder model and create grid divisions within STAR-CCM+. We conduct comparative analysis with existing research findings to validate the accuracy of the computed results in this study. By altering predefined parameters, we investigate the effects of changes in three influencing factors—porosity of the porous media region ε, the shape of the porous area, and additional sinusoidal motion within the porous area—on the fluid dynamics. This analysis yields flow field characteristics and lift coefficient curves under different conditions. Based on the computational results, we summarize general patterns of flow-induced vibration phenomena in porous column models, providing insights for further research on flow-induced vibration problems in porous media and their practical engineering applications.

Flutter limitation of drag reduction by elastic reconfiguration

Through experiments, we idealize a plant leaf as a flexible, thin, rectangular plate clamped at the midpoint and positioned perpendicular to an airflow. Flexibility of the structure is considered as an advantage at moderate flow speed because it allows drag reduction by elastic reconfiguration, but it can also be at the origin of several flow-induced vibration phenomena at higher flow speeds. A wind tunnel campaign is conducted to identify the limitation to elastic reconfiguration that dynamic instability imposes. Here, we show by increasing the flow speed that the flexibility permits a considerable drag reduction by reconfiguration, compared to the rigid case. However, beyond the stability limit, vibrations occur and limit the reconfiguration. This limit is represented by two dimensionless numbers: the mass number and the Cauchy number. Our results reveal the existence of a critical Cauchy number below which static reconfiguration with drag reduction is possible and above which a dynamic instability with important fluctuating loads is present. The critical dimensionless velocity is dependent on the mass number. Flexibility is related to the critical reduced velocity and allows defining an optimal flexibility for the structure that leads to a drag reduction by reconfiguration while avoiding dynamic instability. Furthermore, experiments show that our flexible structure can exhibit two vibration modes: symmetric and anti-symmetric, depending on its mass number. Because the system we consider is bluff yet aligned with the flow, it is unclear whether the vibrations are due to a flutter instability or vortex-induced vibration or a combination of both phenomena.

Analysis on flow-induced vibration of square cylinders with different vibration forms and the flow energy harvesting capacity

This study numerically investigates the flow-induced vibration (FIV) of a single-degree-of-freedom transverse vibration and pivoted rotation of a square cylinder with the Reynolds number (Re) range of 0.7 × 104 to 6 × 104. Different FIV phenomena with Re increasing are reported. In the vortex-induced vibration (VIV) branch, the amplitude and energy harvest efficiency of the transverse vibration are higher than those of the pivoted rotation, and the situation is opposite in the VIV-galloping transition and galloping branches. Checking the wake vortex indicated that the change in the angle of attack caused by the pivoted rotation of the square cylinder was the cause of these phenomena. The most significant feature was that, at the maximum amplitude, a pair of co-rotating vortices (C mode) shed. The transverse vibration had larger vibration amplitudes and lower aerodynamic force and energy harvest efficiency compared with the pivoted rotation in galloping, and the energy harvest efficiency no longer increased with higher Re. The energy harvest efficiency of the pivoted rotation had two outstanding peaks at maximum pivot angles of θmax = 29° and 41.2°, followed by a decreasing trend. For the transverse vibration, the force induced by the vortices cancels each other out so that the energy harvest efficiency almost does not change. For the pivoted rotation, the amplitude, which does not increase, makes it easier for the wake vortex to interact and interfere with the energy harvest procedure.

Resolvent and dynamic mode analysis of flow past a square cylinder at subcritical Reynolds numbers

Flow-induced vibration (FIV) of bluff bodies can occur at subcritical Reynolds numbers (i.e., below the Re of the vortex shedding from fixed bodies). To analyze the mechanism of this subcritical FIV phenomenon, resolvent and dynamic mode analyses are introduced in this work. For laminar flow past a square cylinder, both resolvent and dynamic modes are extracted and investigated. The results indicate that the dominant dynamic mode decomposition mode and the leading response mode are similar. Both modes lead to vortex shedding at supercritical Reynolds numbers, and they vanish below Re = 19 along with the dominant forcing mode. In addition, the first and second resolvent gains separate near the characteristic flow frequency and overlap at Re = 19, indicating the disappearance of the first-order resolvent mode. The disappearance of these critical modes indicates the lowest Reynolds number of FIV instability for flow past a square cylinder.

Effect of stochastic deformation on the vibration characteristics of a tube bundle in axial flow

Design evaluation of nuclear components using numerical methods has typically been focused on nominal geometries and conditions. In reality, the geometry of reactor components and operating conditions can differ from the design on the drawing table. Increasing understanding and safety of nuclear energy systems requires investigating these more realistic conditions as well. An example is the bow of fuel assemblies, a deformation that occurs after some residence time as a consequence of thermal and irradiation effects. A paradigm shift from purely deterministic simulations toward simulations involving stochastic processes can help to meet this demand.One of the aspects in the design assessment of nuclear reactors is flow-induced vibration (FIV). A lot of experimental effort has already been allocated to FIV phenomena in the past, and more recently also numerical approaches have been applied. However, it was not clear to what extent vibration characteristics would change for a geometry different from the design drawing. In this study the effect of a random bow deformation on the vibration behavior of a flexible tube in a rigid bundle is investigated using fluid–structure interaction simulations. As the (stressless) geometry presumably has a stochastic nature, the modal characteristics should be treated accordingly.For this uncertainty quantification of the modal characteristics, the generalized Polynomial Chaos method was applied. First, only the steady flow through the bundle was considered, without simulating the vibration. This sufficiently reduced the computational cost to apply the Monte Carlo method, which was used to validate the more efficient Polynomial Chaos method. This latter method was found adequate to predict the stochastic modal characteristics of the deformed, flexible tube.

Optimization Study of Marine Energy Harvesting from Vortex-Induced Vibration Using a Response-Surface Method

Vortex-induced vibration (VIV) of bluff bodies is one type of flow-induced vibration phenomenon, and the possibility of using it to harvest hydrokinetic energy from marine currents has recently been revealed. To develop an optimal harvester, various parameters such as mass ratio, structural stiffness, and inflow velocity need to be explored, resulting in a large number of test cases. This study primarily aims to examine the validity of a parameter optimization approach to maximize the energy capture efficiency using VIV. The Box–Behnken design response-surface method (RSM-BBD) applied in the present study, for an optimization purpose, allows for us to efficiently explore these parameters, consequently reducing the number of experiments. The proper combinations of these operating variables were then identified in this regard. Within this algorithm, the spring stiffness, the reduced velocity, and the vibrator diameter are set as level factors. Correspondingly, the energy conversion efficiency was taken as the observed value of the target. The predicted results were validated by comparing the optimized parameters to values collected from the literature, as well as to our simulations using a computational-fluid dynamics (CFD) model. Generally, the optimal operating conditions predicted using the response-surface method agreed well with those simulated using our CFD model. The number of experiments was successfully reduced somewhat, and the operating conditions that lead to the highest efficiency of energy harvesting using VIV were determined.

Modelling and prediction on the modal and harmonic response of helix tube in large-scale spiral-wound heat exchangers

Spiral-wound heat exchangers (SWHEs) have been widely used in chemical production processes. As the equipment becomes larger, the SWHEs start facing the problem of failure caused by the flow-induced vibration (FIV) phenomenon. To assure the safety and reliability of the SWHEs, it is important to understand clearly the natural modes of spirally wound coils in different sizes and their response under external excitation. Therefore, a 3D model of the helix tube is established and the helix tubes are fully investigated. The effects of different geometrical parameters on the frequency and vibration amplitude of the helix tubes are performed at each mode, by using the finite element (FE) method. Then, the vibration amplitude analysis of the helix tube under harmonic excitation is carried out, and the dangerous frequency band of the equipment under different geometrical parameters is obtained, which is mainly around 10 Hz to 40 Hz in current domain. Moreover, sensitivity analysis is presented to have a more in-depth investigation into the effects of vibration deformation and frequency, which shows that the biggest influence factor is the helix angle. Finally, machine learning is used to predict dangerous frequency, then case studies are presented to verify the validity of the regression method in which the random forest (RF) model and extreme gradient boosting (XGBoost) have the smallest error, less than 10%. The results are very important for designing SWHEs on large scale to meet the requirement of industry development.

Modelling of Flow-Induced Vibration of Bluff Bodies: A Comprehensive Survey and Future Prospects

A comprehensive review of modelling techniques for the flow-induced vibration (FIV) of bluff bodies is presented. This phenomenology involves bidirectional fluid–structure interaction (FSI) coupled with non-linear dynamics. In addition to experimental investigations of this phenomenon in wind tunnels and water channels, a number of modelling methodologies have become important in the study of various aspects of the FIV response of bluff bodies. This paper reviews three different approaches for the modelling of FIV phenomenology. Firstly, we consider the mathematical (semi-analytical) modelling of various types of FIV responses: namely, vortex-induced vibration (VIV), galloping, and combined VIV-galloping. Secondly, the conventional numerical modelling of FIV phenomenology involving various computational fluid dynamics (CFD) methodologies is described, namely: direct numerical simulation (DNS), large-eddy simulation (LES), detached-eddy simulation (DES), and Reynolds-averaged Navier–Stokes (RANS) modelling. Emergent machine learning (ML) approaches based on the data-driven methods to model FIV phenomenology are also reviewed (e.g., reduced-order modelling and application of deep neural networks). Following on from this survey of different modelling approaches to address the FIV problem, the application of these approaches to a fluid energy harvesting problem is described in order to highlight these various modelling techniques for the prediction of FIV phenomenon for this problem. Finally, the critical challenges and future directions for conventional and data-driven approaches are discussed. So, in summary, we review the key prevailing trends in the modelling and prediction of the full spectrum of FIV phenomena (e.g., VIV, galloping, VIV-galloping), provide a discussion of the current state of the field, present the current capabilities and limitations and recommend future work to address these limitations (knowledge gaps).

Stability analysis for laminar separation flutter of an airfoil in the transitional flow regime

Laminar separation flutter (LSF) is a type of aeroelastic instability phenomenon characterized by small-amplitude low-frequency pitching oscillations of the airfoil. The present study aims to gain insight into the intrinsic dynamics of LSF via data-driven stability analysis. The proposed data-driven approach relies on the autoregressive with exogenous input (ARX) technique to design reduced-order models (ROMs) of unsteady aerodynamics in a state-space format. First, high-fidelity full-order numerical simulations of the LSF phenomenon are performed using the incompressible Unsteady Reynolds-Averaged Navier–Stokes equations and the Shear-Stress Transport k−ω turbulence model with Low-Reynolds-number correction. The calculated LSF responses show good agreement with previous experimental data in the literature. Then, linear stability analysis (LSA) of the aeroelastic system is carried out to reveal the underlying fluid-structure interaction mechanism. The LSA model is developed by coupling the ROM with the structure motion equation. LSA results indicate that the LSF phenomenon is primarily caused by the instability of the structure mode (SM), which is induced by the mutual repulsion effect between one static fluid mode (FM) and the SM. The presence of laminar separation near the trailing-edge of the airfoil can significantly reduce the stability of the static FM, which ultimately strengthens the fluid-structure coupling effect and leads to LSF. We would like to emphasize that LSF is essentially different from other flow-induced vibration phenomena, such as transonic buffeting of an airfoil and vortex-induced vibration of bluff bodies, for which the instabilities are triggered by the coupling between one dynamic FM and the SM. Finally, the effects of the mass ratio, structural damping ratio, and freestream turbulence intensity on the aeroelastic system are also investigated.

Flow-induced vibrations in long rows of cylinders and their links to convective instabilities

Flows past rows of elastically mounted cylinders display a number of flow-induced vibration phenomena that hitherto have proven difficult to categorise in a way that is independent of the number of cylinders in the row. Here, we investigate the flow past six equispaced but independent elastically-mounted cylinders at Reynolds number Re=200 using direct numerical simulations over a wide range of stiffnesses and for three values of the inter-cylinder spacing or pitch p. We make a first attempt at categorising the responses observed in terms of the framework of flow states linked to convective instabilities in rows of rigidly mounted cylinders recently presented in Hosseini, Griffith and Leontini (2020). We show that regardless of pitch, this framework has some success in explaining and collating the flow-induced vibration response for high to moderate stiffnesses (corresponding to low to moderate reduced velocities U∗). Among others, one phenomenon observed that fits this framework is the fact that for some cases, the first and last cylinders in an array can vibrate, while the rest are almost stationary. However, at low stiffness/high U∗, the arrays behave more like a single flexible structure that exhibits waves, which is an inherent fluid-structure mode with no root in the rigidly mounted case.

Interpretable machine learning for insight extraction from rigid cylinder flow-induced vibration phenomena

As the amount of data from numerical simulations and physical experiments is ever-increasing, machine learning techniques have become a growing paradigm shift for scientific study. Developing advanced data analytics techniques is critical in assessing the similarities and differences among different datasets since they can lead to foundational insight into the physical phenomena. This paper presents a framework that combines machine learning predictions, feature selection, and machine learning interpretation to identify important vortex-induced vibration (VIV) features and quantify their contributions to the variability often observed in VIV response. Examples from rigid cylinder forced vibrations and free vibrations are employed to show the framework's effectiveness. Using this framework, we could quickly identify and summarize the key physical insights for VIV, such as the effect of damping on response amplitude, the role of reduced velocity, and the effect of phase angle in controlling the hydrodynamic coefficients. These extracted insights were general in that they correspond well with several independent flow-induced vibration experiments on flexible cylinders. The insights extracted using the proposed framework could help people better understand the structural dynamics in a fluid environment and check the consistency of VIV prediction models.

An elastic rotative nonlinear vibration absorber (ERNVA) as a passive suppressor for vortex-induced vibrations

Vortex-induced vibration (VIV) is a self-excited and self-limited flow-induced vibration phenomenon of importance for both the academic and the technological communities. Particularly for the offshore engineering scenario, VIV plays an important role in the structural fatigue analysis. Hence, VIV suppression is a relevant topic. Among different solutions for VIV mitigation, this paper focuses on the numerical analysis of an elastic rotative nonlinear vibration absorber (ERNVA) as a device for passive suppression. The ERNVA consists of a mass placed at the tip of an axially elastic beam hinged to the cylinder by means of a linear dashpot. In this paper, the hydrodynamic loads are calculated using a wake-oscillator model, allowing comprehensive parametric studies for assessing the influence of the ERNVA parameters on its efficiency for the whole range of reduced velocities associated with the lock-in. Among other novel results, it is found that ERNVA can lead to a $$25\%$$ decrease in the maximum oscillation amplitude, being significantly more efficient than its counterpart characterized by a rigid rotating arm. Passive suppression is obtained not only for the peak, but within a certain range of reduced velocities. Curves showing the influence of the ERNVA parameters on the force coefficients for different values of reduced velocity are also innovative.

Experimental investigation on flow-induced vibration of flexible multi cylinders in atmospheric boundary layer

Experimental investigations of the flow-induced vibration (FIV) of flexible multi cylinders in tandem, side-by-side and staggered arrangements were conducted in an atmospheric boundary layer wind tunnel over a wide spacing ratio and incidence angles. All cylinders were cantilever supported and allowed to vibrate in cross-flow and inline directions. The vibration characteristics and transition features are identified among different configurations, and the responses dependent on reduced velocity under each configuration are discussed. Four regimes of the FIV of tandem cylinders are classified, where cylinder 1 vibrates divergently similar to galloping in Regime Ⅰ (l < 1.6, α = 0°) but is suppressed in Regime Ⅱ (1.6 ≤ l < 3, α = 0°), cylinder 2 always vibrates obviously in all four regimes, and cylinder 3 has a distinct vibration in only Regimes Ⅱ, Ⅲ (3 ≤ l ≤ 5, α = 0°) and Ⅳ (l >5, α = 0°), in which l is the nondimensional center-to-center distance and α is the incidence angle. There are two regimes for side-by-side cylinders, in which a divergent vibration of cylinder 1 is observed in Regime V (l < 1.6, α = 90°) and only cylinder 3 vibrates significantly in Regime VI (1.6 ≤ l ≤ 3.2, α = 90°). The aerodynamic properties analyzed through a prediction method are used to explain the vibration mechanism, in which the negative aerodynamic damping ratio branches sustain the divergent vibration in Regime I. Based on the comprehensive study above, the FIV phenomenon of flexible multi cylinders can be understood in atmospheric environment with nonuniform inflow, high turbulence intensity and subcritical Reynolds numbers. Finally, the potential of harvesting wind energy via this technique, showing the highest efficiency 52% but limited at Ur≥30, is discussed.

Prediction of flow induced vibration of a flat plate located after a bluff wall mounted obstacle

Accurate prediction of Flow Induced Vibration phenomena is currently a field of major interest due to the use of lightweight materials in the automotive and aerospace industry. This article studies the turbulent flow around a wall-mounted obstacle, and the induced deformations produced by the pressure fluctuations on a plate located downstream the obstacle. The methodology used is a combination of experimental tests and numerical simulations. On one side, experiments were carried out in a wind tunnel test facility equipped with Particle Image Velocimetry to characterize the fluid velocity field, and laser vibro-meter to measure the vibrations of the plate. On the other side, Fluid-Structure Interaction (FSI-one-way) has been calculated by considering different turbulence modeling approximations (RANS and LES). Finally, numerical results have been analyzed and validated against the experiments in terms of main flow structures and the vibroacoustic response of the plate.

Experimental device for the study of Liquid–Solid coupled flutter instability of salt cavern leaching tubing

A salt cavern underground gas storage is typically constructed by water solution mining, in which slender leaching tubings are used as the channel for water injection and brine production. Cavern leaching and well workover operations are accident prone owing to leaching tubings being bended excessively and even ruptured. These accidents are caused primarily by flow-induced vibration of leaching tubings. To investigate these flow-induced vibration phenomena, an in-house laboratory device for liquid–solid coupled flutter instability of salt cavern leaching tubing was developed. This experimental device consists primarily of a recirculating flow system, vertical cantilevered pipe test section, and instruments for parameter measurement. The experimental device can be utilized to investigate multiple factors involved in the flow-induced vibration of the leaching tubing, including flexural rigidity, overhang length, and support conditions of tubing string. To verify the adequacy of this device, two sets of experiments have been performed in the air without external space constraints by using a cantilevered silicon rubber and polycarbonate pipes, respectively. Flutter instability phenomena were observed in these experiments. Furthermore, through the study on the length effect, an asymptotic behavior with the critical flow velocity reaching limiting values as the lengths of the pipes increase, is discovered. The present study is conducive to the subsequent experimental step that considers additional factors. Consequently, the device provides adequate in-house experimental conditions for researching the instability mechanism and safety control measures of the leaching tubing.

The effect of mass ratio on the structural response of a freely vibrating square cylinder oriented at different angles of attack

This study reports on an experimental investigation of the effect of mass ratio on the transverse flow-induced vibration (FIV) response of an elastically mounted square cylinder placed at three different incidence angles: two symmetric with respect to the centreplane, α=0° and 45°; and one asymmetric at 20°. These three angles display different dominant FIV phenomena: transverse galloping and combined vortex-induced vibration (VIV) and galloping for α=0°, VIV for α=45°, and higher branch subharmonic (period-doubled) VIV for α=20° (Nemes et al., 2012). The mass ratio is defined as the ratio of the total oscillating mass (m) to the displaced fluid mass (md), m∗=m∕md. The present results show that the mass ratio (m∗=2.64 – 15.00) has a significant influence on the structural vibration response for all FIV phenomena, and can dictate whether two of these modes exist at all. Three primary observations are presented: for the α=0° case, the combined VIV–galloping response is diminished as the mass ratio is increased, and it ceases to exist for m∗⩾11.31; for the α=45° case, the peak values of the normalised oscillation amplitude during VIV are only reduced marginally with increasing m∗, however the body oscillation amplitude in the desynchronised regions is significantly attenuated; for the α=20° case, there exists a critical mass ratio (mcrit∗≃3.50) above which the higher branch subharmonic VIV does not persist.

Experimental investigation on suppressing circular cylinder VIV by a flow control method based on passive vortex generators

Vortex-induced vibration (VIV) is a typical flow-induced vibration phenomenon, which is usually observed in circular cylindrical structures. This study introduces a flow control method based on passive vortex generators (PVGs) for suppressing the VIV of circular cylindrical structures. A series of wind tunnel experiments were performed using rigid circular cylinder models. Vibration tests were implemented using a spring–mass system for verifying the effectiveness of PVGs, and pressure tests were implemented by using a fixed cylinder model for revealing the aerodynamic mechanisms of PVGs qualitatively. Five geometric parameters of PVGs were tested and the optimal parameters were determined during the wind tunnel experiments. The experiment results prove that the maximum root-mean-square values of the vibration amplitudes can be suppressed by more than 80% by attaching PVGs with optimal parameters on the cylinder surface. According to the pressure test results, PVGs designed suitably can suppress vortex shedding in the cylinder wake flow and weaken the spanwise correlation of the cylinder wake flow. Weakening the wake flow spanwise correlation contributes more to controlling the amplitudes of cylinder VIV. In addition to the control effects on the cylinder VIV, some other aerodynamic phenomena of the cylinder with PVGs were observed and analysed.

Numerical analysis on aerodynamic characteristics of short cylindrical terminal-sensitive bullet

The flow-induced lateral vibration phenomenon of the terminal sensitive bullets (TSB) when it is dispersed by the airborne distributor is taken as the research background. Based on the Fluent, the flow around a rotating short cylindrical TSB (L/D &lt; 1) is simulated and analyzed varying with relative rotation velocity at high Re number (1×105 ≤ Re ≤ 3×106). The simulation results show that the flow field structure of the short cylinder with two free ends is different from the symmetry of the short cylindrical flow field with one free end, and there is no horseshoe vortex. Compared to the long cylinder with double free ends, the Cd of the short cylinder is more sensitive to the change of Re. With the increase of Re, the Cd of the short cylinder decreases, and the value is between the infinite cylinder and the sphere in the non-critical region. When the short cylinder rotates at the angular velocity ω, the top vortex bends and deforms to a ‘C’ shape on the leeward side where the fluid is accelerated. Due to the periodic disturbance of the detector, the aerodynamic coefficient of the rotating TSB is periodically vibrated. In a single cycle, the waveform of the cd shows a ‘W’ shape, and the waveform of the cl is ‘M’.

Flow-induced vibration of a square cylinder and downstream flat plate associated with micro-scale energy harvester

The phenomenon of flow-induced vibration (FIV) over a square cylinder at Reynolds numbers, Re = (3.6–12.5 × 103) is numerically studied. This current study provides a detailed explanation of the behaviour of transverse motion of square cylinder with the mass damping ratio, mζ* = 2.48. The computation of FIV is conducted by numerical simulation based on the Unsteady Reynolds Navier-Stokes (URANS) flow field using OpenFOAM software. The first part of the numerical simulation consists of an isolated square cylinder to validate the solution with previous studies. The computation of FIV with a total number of cells, N = 101,662 have shown a comparable pattern of amplitude curve. The coexistence of vortex-induced vibration (VIV) and galloping is observed for a single isolated cylinder. A downstream flat plate is introduced in the second part of the work. Different gaps separation between the cylinder and flat plate (0.1 ⩽G/D ⩽ 3) are simulated. Based on the amplitude curve against reduced velocities 4 ⩽UR⩽ 20, four regimes are identified. According to the power estimation, the optimum gap separation is G/D = 0.1. The harnessed power is higher than a single isolated square cylinder while preserving the robustness for the remote harvesting purpose.

Pilot study about the micro hydropower generation by use of flow induced vibration phenomenon

In order to construct a micro power generation system using a piezo-electric element, power generation was tried using excitation oscillation of the bluff cylinder by the vortex shedding from the bluff cylinder. The bluff cylinder consists of a board spring section in which the piezo-electric element was attached, and a body section. The bluff cylinder was inserted into the water flow, the shape and the submersion depth of the bluff cylinder, and the flow velocity were varied, and the power generation characteristic was investigated. As a result, it was found that it can generate electricity by vortex excitation. It was found that the length and the submersion depth of the body section influence power generation. It was shown that the power generation characteristic changes with cross-sectional shape of the bluff cylinder. The most suitable state was the case where the submersion depth was set to 140 mm with a circular cylinder with a span length of 250 mm. It is important to choose the power generation object which suited the use purpose.