Jihoo Moon

Sohyeun Kang

Seyoung Joung

Cheolgyun Jung

Hyeeun Shim

Minhyeong Lee

Jaehun Yoo

Dong Ju Kim

Janggon Yoo

Dong Hyup Youn

Minho Song

Taekyeong Jeong

Jaewuk Jung

Ki Jong Kim

Junkyu Ham

Ehsan Mahravan

Junyoung Kim

Inuk Song

Seonwoo Lee

Woo Seok Jung

Seung Hun Lee

Jaeho Choi

Ingyu Moon

Hyeonseong Kim

Donghyun Kim

Seongwon Choi

Taehyun Kim

Junsoo Kim

Mohsen Lahooti

Jaehyeock Chang

Daegyu Lim

Dongwook Kim

Hong Ki Lee

Tong Il Park

The lab focuses on Unsteady aerodynamics and hydrodynamics, Fluid-structure interaction, Biological flow, Energy harvesting. We study fluid-structure interaction and multi-phase flow of nature and technology.

연구실은 비정상 공기역학 및 수력학, 유체-구조 상호 작용, 생물학적 흐름, 에너지 수확에 중점을 둡니다.

Cavitation bubble-induced hydrodynamic loading and interfacial deformation in an air pocket

Boiling and liquid film evaporation in a thermosyphon under horizontal vibrations

Shock-induced dispersion patterns of powder with diverse physical properties

Freely falling sphere with a rigid rear-side filament

Dynamics of a Lorentz force activated oscillating jet

Enhancement of wave energy harvesting performance by wave concentration with vertical cylinders

Transient hydrodynamic blockage of gap flow between separated bodies in low-Reynolds-number regime

Dynamic swatch testing of liquid aerosols in a laboratory-sized recirculating wind tunnel

Fire extinguishing device using nanoenergetic materials and dry water

Flow-induced vibration of an S-shaped bluff elastic sheet

Prediction of sloshing pressure using image-based deep learning

Low-order modelling of three-dimensional surface waves in liquid film flow on a rotating disk

Mutual interaction of a collapsing bubble and a nearby viscoelastic solid

Flow-induced rearrangement of a poroelastic cluster

Coordinated suction and blowing of a cylinder array for thrust generation

Asymmetric flapping of a multi-segmented elastic structure

Snap-through instability of a sheet with inclined clamping ends under fluid flow

Gravity-coupled flutter and contact of a flag near a wall

Wall-bounded periodic snap-through and contact of a buckled sheet

Liquid entrainment of the toroidal bubble crossing the interface between two immiscible liquids

Slosh-induced piezoelectric energy harvesting in a liquid tank

Sloshing of a cylindrical tank with pipes under extreme translational excitation

Three-dimensional reconfiguration of an elastic sheet with unidirectional side flaps

Collective dynamics of a stack of inverted flags

Dynamics of a droplet-impact-driven cantilever making contact with the ground

Flow-induced vibration and impact of a cylinder between two close sidewalls

Deep learning model inspired by lateral line system for underwater object detection

Collectively exhaustive hybrid triboelectric nanogenerator based on flow-induced impacting-sliding cylinder for ocean energy harvesting

Bubble collapse and jet formation inside a liquid film

Mitigation of pressure fluctuation in two-phase slug flow by rib geometry 

Starting jet formation through eversion of elastic sheets

Free-surface vortex formation and aeration by a submerged rotating disk

Snap-through oscillations of tandem elastic sheets in uniform flow

Uncertainty quantification of heat trasnfer in a microchannel heat sink with random surface roughness

Water impact of a surface-patterned disk

Flow-induced periodic snap-through dynamics

Contact behavior of a fluttering flag with an adjacent plate

Interactions of the interface of immiscible liquids with an impinging vortex ring

Aerodynamic response of a bristled wing in gusty flow

Stabilized motion of a freely falling bristled disk

Synthetic capsule break-up in simple shear flow

Vortex ring formation coupled with a translating bluff body

Underwater bubble collapse on a ridge-patterned structure

Unsteady concentration transport over an array of cylinders in low-Reynolds-number flow

Optimal configuration of a two-dimensional bristled wing

Flow-induced snap-through triboelectric nanogenerator

Inertia-driven flow symmetry breaking by oscillating plates

Impinging sweeping jet and convective heat transfer on curved surfaces

Aerodynamic interaction of collective plates in side-by-side arrangement

Stability and coupled dynamics of three-dimensional dual inverted flags

Multi-body interaction effect on the energy harvesting performance of a flapping foil

Flow separation control using sweeping jet actuator

Aerodynamic characteristics of unsteady gap flow in a bristled wing

Flow structure and heat transfer of a sweeping jet impinging on a flat wall

Free-fall dynamics of a pair of rigidly linked disks

Large-amplitude flow-induced vibration of cylindrical pendulums

Aerodynamics of a translating comb-like plate inspired by a fairyfly wing

Dynamics of a flag behind a bluff body

Hydrodynamic advantages of a low aspect-ratio flapping foil

Energy harvesting performance and flow structure of an oscillating hydrofoil with finite span

Large-amplitude flapping of an inverted flag in a uniform steady flow – a vortex-induced vibration

Unsteady loading of a vertical-axis turbine in the interaction with an upstream deflector

Flapping dynamics of an inverted flag

Efficiency improvement of straight-bladed vertical-axis wind turbines with an upstream deflector

Vortex dynamics of clapping plates

Characteristics of vortex formation and thrust performance in drag-based paddling propulsion

Flexibility effects on vortex formation of translating plates

Experimental study of three-dimensional vortex structures in translating and rotating plates

Large-amplitude flapping of an inverted flag in a uniform steady flow–a vortex-induced vibration

Flow-separation control using sweeping jet actuator

Collectively exhaustive hybrid triboelectric nanogenerator based on flow‐induced impacting‐sliding cylinder for ocean energy harvesting

Multi-body interaction effect on the energy harvesting performance of a flapping hydrofoil

Daegyoum Kim

The dynamics of an inverted flag are investigated experimentally in order to find the conditions under which self-excited flapping can occur. In contrast to a typical flag with a fixed leading edge and a free trailing edge, the inverted flag of our study has a free leading edge and a fixed trailing edge. The behaviour of the inverted flag can be classified into three regimes based on its non-dimensional bending stiffness scaled by flow velocity and flag length. Two quasi-steady regimes, straight mode and fully deflected mode, are observed, and a limit-cycle flapping mode with large amplitude appears between the two quasi-steady regimes. Bistable states are found in both straight to flapping mode transition and flapping to deflected mode transition. The effect of mass ratio, relative magnitude of flag inertia and fluid inertia, on the non-dimensional bending stiffness range for flapping is negligible, unlike the instability of the …

The effect of an upstream flat deflector on the power output of two counter-rotating straight-bladed vertical-axis wind turbines (VAWTs) was investigated experimentally. Although many studies on the deflector effect have been done for a drag-based Savonius VAWT, there is little information on the performance of a lift-based VAWT with a deflector. If a flat vertical plate is normal to the free-stream wind direction, the local wind speed outside the near-wake region of the plate is larger than the free-stream velocity. Thus, when each of the counter-rotating turbines is positioned outside the near-wake region, its power output increases significantly. The power output increase with the deflector installed is dependent on the width and height of the deflector and the turbine position relative to the deflector.

Motivated by the unsteady force generation of flying animals, vortex formation and vorticity transport processes around small aspect-ratio translating and rotating plates with a high angle of attack are investigated. Defocusing Digital Particle Image Velocimetry was employed to explore the structure and dynamics of the vortex generated by the plates. For both translating and rotating cases, we observe the presence of a spanwise flow over the plate and the consequent effect of vorticity transport due to the tilting of the leading-edge vortex. While the spanwise flow is confined inside the leading-edge vortex for the translating case, it is widely present over the plate and the wake region of the rotating case. The distribution of the spanwise flow is a prominent distinction between the vortex structures of these two cases. As the Reynolds number decreases, due to the increase in viscosity, the leading-edge and tip vortices tend …

The dynamics of a cantilevered elastic sheet, with a uniform steady flow impinging on its clamped end, have been studied widely and provide insight into the stability of flags and biological phenomena. Recent measurements by Kim et al. (J. Fluid Mech., vol. 736, 2013, R1) show that reversing the sheet’s orientation, with the flow impinging on its free edge, dramatically alters its dynamics. In contrast to the conventional flag, which exhibits (small-amplitude) flutter above a critical flow speed, the inverted flag displays large-amplitude flapping over a finite band of flow speeds. The physical mechanisms giving rise to this flapping phenomenon are currently unknown. In this article, we use a combination of mathematical theory, scaling analysis and measurement to establish that this large-amplitude flapping motion is a vortex-induced vibration. Onset of flapping is shown mathematically to be due to divergence instability …

The energy harvesting performance and resulting flow structures of a hydrofoil oscillating in pitch and heave are studied experimentally in a water flume. The shape of a hydrofoil cross-section is shown to have negligible influence on the power generation for the geometries tested. It is found that contribution to efficiency from heaving motion increases with reduced frequency at optimal pitching amplitude. However, contribution to efficiency from pitching motion decreases with reduced frequency because the development of a leading-edge vortex during the stroke is delayed at the high reduced frequency. Increasing the aspect ratio of the hydrofoil leads to a higher contribution to efficiency from heaving over the range of aspect ratios considered in this study. However, the effect of the aspect ratio on efficiency from pitching is negligible. When end plates are mounted at both ends of the hydrofoil, heaving power …

While an impinging jet has been widely investigated because of its remarkable convective heat transfer performance, the impingement of a sweeping jet which undergoes periodic oscillation has drawn little interest. We experimentally examined the heat transfer of a sweeping jet impinging on a flat wall for several Reynolds number and nozzle-to-plate spacings and discovered unsteady flow structure to characterize heat transfer capability. Local Nusselt number on the wall was evaluated by measuring temperature with thermocouples, and a flow was visualized quantitatively using particle image velocimetry. The distribution of the Nusselt number is different from that of a round jet, exhibiting two distinct regions. Near the center of a sweeping jet, a high Nusselt number zone is formed without a noticeable peak commonly observed in a round jet. Away from the central region, the Nusselt number decreases …

IMPROVED aerodynamic designs and new aerodynamic technologies will play a vital role in improving the nextgeneration aircraft’s performance and contribute strongly to the product cost and operability. Active flow control (AFC) is one of the promising technologies to control boundary-layer separation, mixing, and noise. In recent years, actuators for AFC and especially fluidic oscillators have received much interest. The state of the art of improving aerodynamic performance [1], AFC actuators [2], and fluidic oscillators [3] was described in recent review papers. Fluidic actuators increase momentum in the local flowfield by fluid injection. Sweeping jet (SWJ) actuators belong to this category of actuators, and they are based on fluidic oscillators with no moving parts [2], as shown in Fig. 1. An SWJ actuator emits a continuous but spatially oscillating jet at the outlet when pressurized with a fluid [4]. The oscillations are …

Several characteristics of drag-based paddling propulsion are studied with a simple mechanical model and a measurement technique for mapping three-dimensional flow fields. In drag-based propulsion, the temporal change of the vortex strength is an important parameter in the relationship between vortex formation and thrust generation. Our results indicate that spanwise flow behind the paddling propulsor significantly affects tip vortex development and thrust generation. The distribution of spanwise flow is dependent on the propulsor shape and the Reynolds number. A delta-shaped propulsor generates strong spanwise flow compared with a rectangular propulsor. For the low Reynolds number case, spanwise flow is not as strong as that for the high Reynolds number case. Without sacrificing total impulse, the flexible propulsor can smooth out thrust peaks during sudden stroke motions, which is favorable for …

Vortex structures made by impulsively translating low aspect-ratio plates are studied experimentally using defocusing digital particle image velocimetry. The investigation of translating plates with a 90° angle of attack is important since it is a fundamental model for a better understanding of drag-based propulsion systems. Rectangular flat-rigid, flexible and curved-rigid thin plates with the same aspect ratio are studied in order to develop qualitative and quantitative understanding of their vortex structures and hydrodynamic forces. We find that the vortex formation processes of all three cases are drastically different from each other. The interaction of leading-edge vortices and tip flow near the tip region is an important mechanism to distinguish vortex patterns among these three cases. The drag trends of three cases are correlated closely with vortex structure and circulation. The initial peak of hydrodynamic force in the …

Recently, flow-induced vibration and aeroelastic flutter have been considered to be an attractive energy source in renewable energy harvesting systems. However, irregular and random motions in the fluid-structure coupled dynamics greatly deteriorate the consistency and efficiency of the output power performance. Here, we report a novel mechanism of a periodic snap-through triboelectric energy harvester based on the bi-stable property of structural buckling and integrated dielectric-electrode layers made of PDMS-sealed Cu nanowire-Cu mesh. Under wind, a buckled elastic sheet experiences a periodic snap-through oscillation with a rapid transition between two opposite phases. In a regime with a large distance between two side walls, the critical free-stream velocity needed to initiate snapping increases as the wall distance becomes larger. By contrast, for a small wall-distance regime, the critical velocity …

For the sustainable application of remote sensing and monitoring in the ocean environment, energy harvesting technology based on flow‐induced vibration is in the spotlight. Herein, based on the flow‐induced self‐excitation of an impacting‐sliding cylinder, a collectively exhaustive hybrid triboelectric nanogenerator (TENG) is reported, that utilizes both freestanding‐sliding (FS) and contact‐separation (CS) modes. Most importantly, the flow‐induced impacting cylinder (FIC) between two side walls is newly implemented to resolve the critical problem of the lock‐in phenomena occurring in conventional vortex‐induced vibration systems of circular cylinders. Owing to the presence of two side walls, the FIC based TENG (FIC‐TENG) shows a stable electrical power generation in a wide range of flow velocity (0.05–1.02 m s −1 ) without lock‐in phenomena. In addition, the collectively exhaustive FIC‐TENG can be used to …

The effect of an upstream bluff body on energy harvesting performance of a heaving and pitching hydrofoil is investigated numerically using a two-dimensional immersed boundary method at R e= 1000. The presence of the upstream body changes flow structure around the hydrofoil and enhances efficiency significantly by two mechanisms. Mutual interaction of the vortex shed from the upstream body and the leading-edge vortex of the hydrofoil precipitates the separation of the leading-edge vortex from the hydrofoil and its streamwise transport. The incoming flow deflected by the upstream body changes the effective angle of attack for the hydrofoil. These phenomena significantly increase heaving force and pitching moment during stroke reversal, and major contribution to efficiency enhancement is from the change in pitching moment. 30% increase in efficiency, relative to a hydrofoil without an upstream body, can …

Flow-induced vibration of an elastic structure such as a flag has drawn attention recently because of its complicated coupling mechanisms and potential application to energy harvesting. For both air and water flows, we experimentally investigate the effect of an upstream bluff body on the dynamics of two types of a downstream flag, a conventional flag and an inverted flag, on and off a midline. In contrast to the conventional flag, the trailing edge of the inverted flag is clamped, and its leading edge is free to move. By using smoke visualization and particle image velocimetry, the interaction of the flag with the vortices shedding from the bluff body was also identified. With the deployment of a bluff body, the conventional flag displays two distinct periodic flapping modes. While synchronization with the vortices shedding from the bluff body and a resultant fundamental mode appear in a low free-stream velocity range for the …

A micro-scale flying insect has a unique wing configuration consisting of a central frame and several bristles. For the low-Reynolds-number regime in which the insect lives, the bristled wing utilizes a virtual fluid barrier inside gaps produced by strong viscous diffusion of shear layers to overcome its morphological limitations. Considering the unsteady flapping motion of such a wing, the aerodynamic characteristics of gap flow formation are investigated numerically using a two-dimensional bristled wing model for a wide range of Reynolds numbers. Inside a gap between bristles, the development of a stopping vortex during the deceleration phase and its effect on the extinction of an existing vortex generated at the same edge are dependent on the Reynolds number, which leads to a significant change in vorticity distribution at stroke reversal even with just a small change in the Reynolds number. As the Reynolds …

The application of an impinging sweeping jet, which oscillates periodically with a large angle, to convective heat transfer has received attention owing to its capability to provide a more spatially uniform and enhanced heat removal rate when compared to a steady jet. Herein, we study how the surface curvature affects the heat transfer performance of a sweeping jet and couple it with the representative flow characteristics. Heat transfer measurement and quantitative flow visualization are conducted experimentally for concave and convex surfaces as well as a flat surface. Whereas concave surfaces have a better heat transfer rate than a flat surface, the enhancement of the heat transfer is relatively small for a convex surface. For both concave and convex surfaces, the Nusselt number does not increase monotonically with the curvature magnitude but has a peak for a moderate curvature. The variation in heat transfer …

Unlike the smooth wings of common insects or birds, micro-scale insects such as the fairyfly have a distinctive wing geometry, comprising a frame with several bristles. Motivated by this peculiar wing geometry, we experimentally investigated the flow structure of a translating comb-like wing for a wide range of gap size, angle of attack, and Reynolds number, Re= O (10)− O (10 3), and the correlation of these parameters with aerodynamic performance. The flow structures of a smooth plate without a gap and a comb-like plate are significantly different at high Reynolds number, while little difference was observed at the low Reynolds number of O (10). At low Reynolds number, shear layers that were generated at the edges of the tooth of the comb-like plate strongly diffuse and eventually block a gap. This gap blockage increases the effective surface area of the plate and alters the formation of leading-edge and trailing …

This experimental study reports the collapse of an underwater bubble near a patterned structure with ridges and grooves. When a bubble is generated by a spark above a ridge, the entire bubble collapses toward the structure after its full expansion, or it is split into two smaller bubbles because of a radial jet induced by bubble contraction. These distinct collapse modes are dependent on the surface geometry of the structure and determined by the contracting speed of a bubble part inside the cross section of an adjacent groove. For a bubble that collapses in a groove, water flows induced from the tops of adjacent ridges collide with each other in the middle of the groove cross section, and this collision occurs if the effective width of the groove is small enough. For the bubble-splitting radial jet mode on the ridge and the collision mode in the groove, some energy of the bubble is lost during its contraction and …

In contrast to common continuous wings, microscopic flying insects such as fairyfly and thrips possess extraordinary wings that comprise several bristles. In the low-Reynolds-number environment inhabited by these insects, a bristled wing benefits from the formation of virtual fluid barriers that prevent flow leakage in the gaps of bristles. In this study, the optimal configuration regarding the aerodynamic performance of simple bristled-wing models is investigated numerically in terms of the Reynolds number and the distance between bristles, which are known to be important parameters for determining the effectiveness of a virtual fluid barrier. Inspired by the inherent characteristics of low-Reynolds-number flow, we provide new insights into the aerodynamics of a bristled wing by using a scaling parameter that combines these two independent parameters: effective gap width. In addition, the force ratio is scaled with the …

Vortex formation and force generation of clapping plates with various aspect ratios ( and stroke angle.

We investigate the characteristics of free-surface vortex (FSV) formation and aeration processes in a self-ingested reactor. A disk with a protruded ridge rotating in a water tank is used as a simplified model. First, flow velocity fields on the FSV surface and the disk are obtained analytically using a semi-empirical method. From the bottom view of the impeller, we observe bubbles separated from two air pockets formed behind the ridge as the interface of the air pockets becomes fluctuated. Then, void fraction distribution along the vertical direction by rising bubbles is established theoretically and confirmed by experimental measurements. These results and the measured total void fraction data of the tank are used to show that the turbulence cascade energy near the disk is converted into the surface tension energy of bubbles and is responsible for aeration.

Applied Fluid Mechanics Laboratory at KAIST

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연구실 소개

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알럼나이가 간 회사

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연구실 논문 목록

Cavitation bubble-induced hydrodynamic loading and interfacial deformation in an air pocket

Boiling and liquid film evaporation in a thermosyphon under horizontal vibrations

Shock-induced dispersion patterns of powder with diverse physical properties

연구실 보유 특허

대학별 입시끈

우리 연구실 모집

교수님 소개

김대겸

연구실 키워드

알럼나이가 간 회사

연구실 지원 방법

대우 조건

연도별 논문 인용수

저널 & 학회 논문 출판 수

연구실 논문 목록

Cavitation bubble-induced hydrodynamic loading and interfacial deformation in an air pocket

Boiling and liquid film evaporation in a thermosyphon under horizontal vibrations

Shock-induced dispersion patterns of powder with diverse physical properties

연구실 보유 특허

최근 3년간 연구실적 높은 연구실

대학별 입시끈

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