Kim Boon Lua

National Yang Ming Chiao Tung University, Mechanical Engineering, Faculty Member

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Unsteady aerodynamics, VIV, energy harvesting, fluid structure interaction of unsteady flapping wings, high angle of attack aerodynamics and PIV.
Phone: +8863571212155123
Address: https://aerotech.nctu.edu.tw/

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Mahmoud Farag

American University in Cairo

Nesreen ghaddar

American University of Beirut

BORA YILDIRIM

Hacettepe University

Antonio Bula

Universidad del Norte - Barranquilla, Colombia

naveen noronha

Visvesvaraya Technological University

Isad Saric

University of Sarajevo

Richard Crawford

The University of Texas at Austin

Chandramouli Padmanabhan

IIT Madras

Umit Unver

Yalova University

mahmoud hafiz

Al-Azhar University

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Papers by Kim Boon Lua

Numerical investigation of in-line and staggered fins arrangements on liquid mixer

Research Square (Research Square), Aug 16, 2023

This paper numerically analyzed the liquid mixing performance of a T-mixer having fins in two dis... more This paper numerically analyzed the liquid mixing performance of a T-mixer having fins in two distinct arrangements, i.e., in-line and staggered. The effects of fin arrangements on the liquid flow characteristics in the mixing channel are assessed, and it can be profoundly indicated that the induced transverse flow tends to promote better liquid mixing. Comparatively, a mixer with a staggered fin arrangement yields superior mixing performance than that of an in-line fin arrangement, owing to a greater transverse flow. This forces the bulk of the liquid to flow alternatively through both halves of the mixing channel. Supplementary to the better mixing performance attained, a mixer with staggered fins also yields a lower pressure drop. When fins are placed perpendicular to the axial flow direction (i.e., 𝜃 = 0 0 ), the pressure drop yielded by in-line fin arrangement is remarkably high (> 60 times that of the basic T-mixer and > 6 times than that of the staggered fin arrangement). The superiority of the staggered fins on liquid mixing is also observed for flows at different Reynolds numbers, ranging from 0.1 to 10.

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A Study on the Wake Regime Control and Drag Reduction Using Single Splitter Plate for a Flow Past a Semicircular Cylinder

Lecture notes in mechanical engineering, 2020

In this paper, a low Reynolds number flow (Re = 100) around the semicircular cylinder of diameter... more In this paper, a low Reynolds number flow (Re = 100) around the semicircular cylinder of diameter D with and without splitter plate is numerically investigated using in-house developed flexible forcing IB—LBM scheme. The length of the splitter plate is systematically varied from 0.5D to 4.0D to investigate its effect on the flow structure and on the vortex-induced forces. The recirculation region behind the semicircular cylinder is increased with an increase in the length of the splitter plate, and as a consequence the base pressure is recovered, and the time-averaged drag coefficient is reduced. Complete suppression of the fluctuating lift coefficient and von Karman vortex shedding is noticed for a splitter plate of length 4.0D for which a maximum drag reduction of around 32% is found. The wake regime as a function of splitter plate length is thoroughly analysed.

On the aerodynamic effects of pitching phase angle on a two-dimensional hovering wing

This paper reports a fundamental investigation of the effects of pitching phase angle on the aero... more This paper reports a fundamental investigation of the effects of pitching phase angle on the aerodynamics of a two- dimensional (2D) flapping wing executing simple harmonic motion in hovering mode. Direct force measurement and digital particle image velocimetry (DPIV) were employed to obtain the time-dependent aerodynamic forces acting on the wing and the associated flow structures, respectively. Six pitching phase

Thrust Enhancement on a Two Dimensional Elliptic Airfoil in a Forward Flight

Zenodo (CERN European Organization for Nuclear Research), Jan 21, 2016

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Effect of the rear wing size on the thrust performance of the two-dimensional tandem flapping wing

A study of wake structures of a heaving two-dimensional elliptic airfoil using DPIV technique

45th AIAA Aerospace Sciences Meeting and Exhibit, 2007

Collection of Technical Papers - 45th AIAA Aerospace Sciences Meeting53432-344

On the study of the pitch angular offset effects at various flapping frequencies for a two-dimensional asymmetric flapping airfoil in forward flight

Physics of Fluids, 2024

This article explores the aerodynamic performance of a two-dimensional elliptical airfoil undergo... more This article explores the aerodynamic performance of a two-dimensional elliptical airfoil undergoing sinusoidal heaving and asymmetric pitching motions in forward-flight conditions for the Strouhal number (St) range of 0.1–0.6. The study employs numerical simulations and water tunnel experiments to investigate the effects of non-zero pitch angular offset angles (θoffset) while maintaining a fixed Reynolds number of 5000 and an effective angle of attack amplitude of 15° at the pivot location. The θoffset is varied from −15° to +15° at 5° intervals. The present research shows that these parameters significantly impact the leading-edge effective angle of attack, flow velocity, and the formation of high-pressure regions, which are crucial factors in thrust and lift generation throughout the flapping cycle. Moreover, the pitch angle determines whether the resultant force favors thrust or lift. It is observed that the cyclic time-averaged lift consistently increases with θoffset, surpassing symmetric cases (θoffset = 0°). Conversely, the cyclic time-averaged thrust is lower for non-zero θoffset values. Increasing St enhances both cyclic time-averaged thrust and lift up to the respective critical Sts, after which their performance declines. Notably, the critical St of cyclic time-averaged lift exceeds that of cyclic time-averaged thrust; interestingly, their values are invariant with θoffset. Moreover, in the conditions where thrust efficiency maximizes, lift efficiency attains a minimum value and vice versa. So, depending upon the application, one needs to suitably select the pitch angular offset and flapping frequency to maximize thrust or lift performance.

Flow Past an Oscillating Bi-Convex Aerofoil

Proceeding of Third Symposium on Turbulence and Shear Flow Phenomena, 2003

Design and characterization of a silicon piezoresistive three-axial force sensor for micro-flapping wing MAV applications

Proceedings of SPIE, Mar 4, 2015

ABSTRACT

Experimental study on the wing-wake interaction of a flapping wing Micro Aerial Vehicle

This work presents an experimental study of the aerodynamics of different types of wings during t... more This work presents an experimental study of the aerodynamics of different types of wings during the clap-and- peel mechanism on a hovering flapping wing Micro Aerial Vehicle (MAV) platform. A comprehensive analysis of the phenomenon through force measurement, motion capture and flow measurement using Particle Image Velocimetry in a fixed position was performed. The flow field around the two types of wings with identical dimensions but different deformation characteristics is compared to understand the role of their flexibility in enhancing the benefits of clap-and-peel effect. The two wings have different configurations of carbon fiber rod stiffeners. Varying degrees of flexibility along the camber were observed in the two wings. Insights were obtained on the correlation between the chordwise camber of wings and their influence on force generation and energy efficiency of the flapping wing MAV. The relative strength and location of the leading edge vortices were compared. One of the wings exhibited higher average lift force by 32% and higher average power efficiency by 18% than the other. For Particle Image Velocimetry, Rhodamine-B fluorescent particles were used to seed the flow, over the conventional fog and oil droplets. This mitigated the optical obstruction due to reflection of the wing through the use of optical filters on camera lens.

DBD-Streamer Mode Transition of Atmospheric-Pressure Plasma Jet Applied on Water with Varying Distance and AC Power

Physica Scripta

The discharge of atmospheric-pressure plasma jet (APPJ) applied on the water was studied by varyi... more The discharge of atmospheric-pressure plasma jet (APPJ) applied on the water was studied by varying an air gap between a powered electrode and the water, and the alternating current power. It was found that the streamers were converged by the air flow to form a streamer bridge to allow current flow across the air gap to transition from a dielectric barrier discharge (DBD) mode to a streamer mode. Because the AC power alternates periodically, this study proposed an analysis without the parameter of time by the voltage amplitude to power characteristic. It was found that the longer distance required higher voltage amplitude and power to transition. Prior research of plasma rarely mentioned the real power and the reactive power, which are essential for electric devices. Because different discharge mode produces different species, this study proposed a simple method to analyze and predict discharge modes based on the power factor, which presents the relationship of the real power and th...

Drag reduction study of naturally occurring oscillating axial flow induced by helical corrugated surface in Taylor–Couette flow

Physics of Fluids

This study investigates drag reduction capability of naturally occurring-oscillating axial second... more This study investigates drag reduction capability of naturally occurring-oscillating axial secondary flow (ASF) induced by helical-corrugated surface in Taylor–Couette flow (TCFHelical) for three values of pitch to wavelength ratios (P* = 1, 2, and 3) and amplitude to wavelength ratio(A*) of 0.25. As reported in Razzak et al. [“Numerical study of Taylor Couette flow with longitudinal corrugated surface,” Phys. Fluids 32(5), 053606 (2020)], emergence of naturally occurring-oscillating ASF induced by longitudinal-corrugated surface in TCF (TCFLongitudinal) and increasing trend on its magnitude with Reynolds number (Re) results in the occurrence of drag reduction. This has motivated us to study the possibility of enhancing drag reduction by maintaining a consistently increasing trend with Re in the magnitude of naturally occurring-oscillating ASF induced by the helical-corrugated surface on the stationary outer cylinder in TCF. From flow structures, steady ASF with non-zero mean is obs...

On the limits of wavy cylinder wavelength and amplitude for effective wake and vortex-shedding control

Journal of Marine Science and Technology

An experimental time-resolved particle-image velocimetry study was conducted on wavy cylinders po... more An experimental time-resolved particle-image velocimetry study was conducted on wavy cylinders possessing wavelength (λ) and amplitude (a) combinations that are significantly different from earlier studies at ReDm = 2700. Results show that vortex formation length increases as the wavelength decreases from λ/Dm = 2.4 to 1.2, but decreases when the latter decreases to λ/Dm = 0.6. Amplitude increments lead to significant vortex formation length growths and reductions at the saddles/nodes of λ/Dm = 2.4 and 1.2 wavy cylinders, respectively. In contrast, λ/Dm = 0.6 wavy cylinders produce significantly shorter vortex formation lengths like a baseline cylinder, regardless of amplitude. Regular reversed flow “lobes” are observed for λ/Dm = 2.4 and 1.2 wavy cylinders, but not λ/Dm = 0.6 ones, which lead to variations in the spanwise vortex formation lengths. Proper orthogonal decomposition (POD) analysis shows that only a/Dm = 0.4, λ/Dm = 0.6 wavy cylinder has the same vortex-shedding frequency as the baseline cylinder. Other POD results also demonstrate that the vortex-shedding behaviour between λ/Dm = 0.6 wavy and baseline cylinder is very similar. The present study shows that there exists a minimal wavelength below which that coherent streamwise vortices will not be produced and wake control benefits of wavy cylinders will be considerably reduced.

Computational Investigation of Multiple Oscillating Hydrofoils and its Effect on Thrust Augmentation

MATEC Web of Conferences, 2021

Previous investigations of flapping hydrofoils for the purpose of thrust production have been lim... more Previous investigations of flapping hydrofoils for the purpose of thrust production have been limited to one or two in tandem. Tandem foils were found to have superior performance because the performance of the aft foil was augmented by the vortices shed from the fore foil. It is however not clear if increasing the number of foils will continue to have increased performance or if there exist an optimal number after which the overall performance either stagnates or reduces. A 2D computational study was conducted to investigate the effect of increasing the number of hydrofoils to four at a Reynolds number of 8000 flapping in-phase and out-of-phase. Optimal and sub-optimal conditions found previously with tandem hydrofoils were found also be applicable to three and four hydrofoils.

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Optimization of Simple and Complex Pitching Motions for Flapping Wings in Hover

AIAA Journal, 2018

Streamwise counter-rotating vortices generated by triangular leading edge pattern in flat plate boundary layer

Journal of Visualization, 2016

A series of flow visualizations were conducted to qualitatively study the development of streamwi... more A series of flow visualizations were conducted to qualitatively study the development of streamwise counter-rotating vortices over a flat plate induced by triangular patterns at the leading edge of a flat plate. The experiments were carried out for a Reynolds number based on the pattern wavelength (λ) of 3080. The results depict the onset, development and breakdown of the vortical structures within the flat plate boundary layer. Moreover, the effect of one spanwise array of holes with diameter of 0.2λ (=3 mm) was examined. This investigation was done on two different flat plates with holes placed at the location x/λ=2 downstream of the troughs and peaks. The presence of holes after troughs does not show any significant effect on the vortical structures. However, the plate with holes after peaks noticeably delays the vortex breakdown. In this case, the "mushroom-like" vortices move away from the wall and propagate downstream with stable vortical structures. The vortex growth is halted further downstream but start to tilt aside.

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Drag reduction study of naturally occurring oscillating axial flow induced by helical corrugated surface in Taylor Couette flow

Physics of Fluids, 2023

On the limits of wavy cylinder wavelength and amplitude for effective wake and vortex-shedding control

Journal of Marine Science and Technology, 2023

Effects of the Pivot Point Locations on the Propulsive Performance of a Two-Dimensional Flapping Elliptic Airfoil with a Pitching Angular Offset

Lecture notes in mechanical engineering, 2023

Side Force on an Ogive Cylinder: Effects of Control Devices

AIAA Journal, 2000

This study is an extension of our earlier work, which examined the effectiveness of using an elli... more This study is an extension of our earlier work, which examined the effectiveness of using an elliptic tip to control the side force acting on an ogive cylinder. In that study, only one tip was considered, and thus the effect of tip eccentricity on the side force was not known. In the present study, we examine another elliptic tip of a smaller eccentricity to get an insight into how tip eccentricity affects the local and overall side force distribution. Our measurements show that, although the smaller eccentricity tip has a side force distribution similar to that of the larger eccentricity tip, there are some major differences in their flow characteristics. For example, the larger eccentricity tip is found to reduce the onset angle of attack and delay the disappearance of the side force to a higher angle of attack. Furthermore, when α 60 deg, only the lower eccentricity tip displays a hysteresis effect in its side force distribution. To the best of our knowledge, this phenomenon has not been observed on an elliptic tip before, even though a similar phenomenon has been observed on a conical body with a rounded tip when the cone was subjected to unsteady bleeding

Numerical investigation of in-line and staggered fins arrangements on liquid mixer

Research Square (Research Square), Aug 16, 2023

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A Study on the Wake Regime Control and Drag Reduction Using Single Splitter Plate for a Flow Past a Semicircular Cylinder

Lecture notes in mechanical engineering, 2020