Article
Engineering, Marine
Ran Li, Jie Gong, Wei Chen, Jie Li, Wei Chai, Chang-kyu Rheem, Xiaobin Li
Summary: Numerical simulations were conducted to investigate the vortex-induced vibrations of a two-degree-of-freedom rotating cylinder near a wall. The effects of gap ratio, reduced velocity, and rotational rate on amplitude response, wake variations, and fluid forces were analyzed. The results revealed the correlative mechanism in the wake-hydrodynamics-vibration. It was found that the wall has a dominant influence on the vortex-induced vibration, which weakens with the increase of the gap ratio and becomes negligible when H/D > 1.1.
JOURNAL OF MARINE SCIENCE AND ENGINEERING
(2023)
Article
Mechanics
Minho Song, Seongwon Choi, Daegyoum Kim
Summary: The dynamic behaviors of an interface between two immiscible fluids deformed by a vortex ring are studied experimentally. Different deformation modes of the interface exhibit similarity in terms of interfacial deformation profiles, which are closely related to the Froude number. An empirical dimensionless parameter is introduced to quantitatively characterize the interfacial deformation, considering the effects of fluid inertia, gravitation, and surface tension.
Article
Engineering, Marine
Junjie Wang, Renliang Chen, Zhiming Yu, Jiaxin Lu
Summary: Ground and water interferences significantly affect the safety of takeoff and landing for Quad Tilt-Rotor (QTR) aircraft. An unsteady numerical simulation method suitable for amphibious QTR aircraft is established and verified through ground tests. The study explores the distinct aerodynamic characteristics of the QTR aircraft in water and ground effects (IWE and IGE) and compares them to those out of ground effect (OGE). Results indicate that the wing, ground or water surface strongly affects the QTR's aerodynamic performance by influencing the downwash flow form the rotors. The lift and torque coefficients exhibit irregular fluctuations during IGE compared with OGE. However the distribution of lift and torque coefficients become more periodic and regular during IWE due to the flexible water surface.
Article
Mechanics
C. R. Constante-Amores, T. Abadie, L. Kahouadji, S. Shin, J. Chergui, D. Juric, A. A. Castrejon-Pita, O. K. Matar
Summary: This study investigates the effect of insoluble surfactants on the spatio-temporal evolution of turbulent jets through three-dimensional numerical simulations. The results show that surfactant-induced Marangoni stresses play a crucial role in the formation of coherent vortex structures and greatly influence the development of three-dimensional interfacial dynamics. The study also provides theoretical expressions for the mechanisms influencing the circulation production rate in the presence of surfactants.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Fu-Sheng Qiu, Bo-Wen Wang, Yi-Ming Du, Hui-Yuan Qian
Summary: This study simulated and analyzed the influence of flight attitude on the aerodynamic characteristics of dandelion seeds using a simplified rigid pappus model. The results showed that different attitudes can lead to the breakdown of the vortex ring structure and a loss of drag performance.
Article
Engineering, Aerospace
Jiaxin Lu, Yang Lu, Junjie Wang, Xice Xu, Mengxue Shao
Summary: This article studies the quasi-vortex-ring state (QVRS) of a multi-axis propulsive wing aircraft during vertical descent and proposes recovery strategies for the QVRS and windmill-brake state (WBS).
AEROSPACE SCIENCE AND TECHNOLOGY
(2023)
Article
Engineering, Marine
Jingming Dong, Rongxuan Meng, Jing Chen, Mushan Liu, Xiao Zhong, Xinxiang Pan
Summary: A novel self-excited oscillation nozzle (SEON) with a circular arc curve chamber was designed to enhance the cavitation performance. Numerical analysis was conducted to explore the influences of the chamber wall profile on the cavitation performance of the circular arc curve chamber SEON. The results showed that the circular arc curve chamber structure could create a larger central cavitation volume, leading to improved cavitation performance compared to the broken-line chamber SEON.
JOURNAL OF MARINE SCIENCE AND ENGINEERING
(2023)
Article
Engineering, Aerospace
Pavel Makeev, Yuri M. Ignatkin, Alexander Shomov
Summary: The study utilized the original free vortex wake model for numerical investigation, analyzing aerodynamic characteristics and VRS boundaries. The results were compared with other studies and can supplement existing experimental and computational research in this area.
CHINESE JOURNAL OF AERONAUTICS
(2021)
Article
Engineering, Aerospace
Haocheng Yu, Xinguang Cui, Guosheng Li, Jianguo Zheng
Summary: This study investigates the flow separation control over rotating rotor blades in hover using an AC-DBD plasma actuator through numerical simulation, possibly for the first time. The results show that the plasma excitation can significantly inhibit the flow separation and enhance the aerodynamic characteristics of the rotor blades. The controlled flow is a significant improvement over the baseline case, achieved by inducing spanwise vortices that reattach the separated flow to the blade surfaces.
Article
Thermodynamics
Lijun Wang, Bingyu Chen, Yuncong Jiang, Xiaokang Yan
Summary: The study compared the heat transfer capacity of concave VG, convex VG, and trapezoidal VG, with concave VG found to have a more reasonable heat transfer capacity, enhancing heat transfer efficiency and reducing resistance loss. Nusselt number (Nu) has a strong correlation with volume averaged turbulent dissipation rate and wall shear stress, with a correlation coefficient of 0.935.
INTERNATIONAL COMMUNICATIONS IN HEAT AND MASS TRANSFER
(2021)
Article
Engineering, Aerospace
Pengcheng Cui, Hongyin Jia, Jiangtao Chen, Guiyu Zhou, Xiaojun Wu, Mingsheng Ma, Huan Li, Jing Tang
Summary: This paper investigates the computational simulation of unsteady multi-body separation characteristics and flow characteristics of hypersonic shroud separation at Mach 7.0. The study identifies various vortexes and shock waves generated during the separation process and discovers the unsteady expansion-transfer-dissipation process of an A-type vortex. The findings provide useful insights for the design of near-space hypersonic vehicles.
Article
Engineering, Marine
Vatsal Dhamelia, Ming Zhao, Pan Hu
Summary: Numerical simulations are conducted to investigate the local scour below a vertically vibrating subsea pipeline for various gap ratios and reduced velocities. The results reveal sudden changes in scour rate and vibration amplitude at a critical time within the lock-in regime. The critical time corresponds to changes in response mode due to scour, and two types of critical times are identified. The maximum scour depth consistently occurs at a reduced velocity of Ur = 5 for all studied gap ratios.
Article
Green & Sustainable Science & Technology
Dylan S. Edirisinghe, Ho-Seong Yang, S. D. G. S. P. Gunawardane, Ali Alkhabbaz, Watchara Tongphong, Min Yoon, Young -Ho Lee
Summary: Waste energy recovery is crucial for improving energy efficiency. The gravitational water vortex power (GWVP) is a suitable micro-hydro extraction method for industrial waste-water discharge. This study focused on the numerical and experimental investigation of a GWVP plant based on a fish farm's discharge water flow. Simulations and experiments were conducted to evaluate the performance under different conditions. The designed GWVP plant successfully reached the target power output, proposing an actual site application for sustainable energy recovery.
Article
Mechanics
L. Xia, Y. Hua, J. G. Zheng
Summary: The study investigates leading edge flow separation control over a stalled airfoil using a fluidic oscillator, revealing the interaction between oscillating jet and external crossflow leads to the production of spanwise vortices, mitigating flow separation. It is found that a higher mass flow usually leads to a better flow control performance.
Article
Thermodynamics
Weilin Liao, Zijian Huang, Hu Sun, Xin Huang, Yiqun Gu, Wentao Chen, Zhonghua Zhang, Junwu Kan
Summary: The numerical study investigates the effect of the downstream plate on the vortex-induced vibration (VIV) of the cylinder using the fluid-structure interaction method. The cylinder's dynamic characteristics are analyzed based on the plate height and gap length between the plate and the cylinder. The study reveals the transition from VIV to galloping and the enhancement of vibration under plate interference.
Article
Cardiac & Cardiovascular Systems
Hyung Oh Kim, Bo Jiang, Eric K. W. Poon, Vikas Thondapu, Chong-Jin Kim, Osamu Kurihara, Makoto Araki, Akihiro Nakajima, Chris Mamon, Jouke Dijkstra, Hang Lee, Andrew Ooi, Peter Barlis, Ik-Kyung Jang
Summary: This study investigated the evolution of hemodynamic parameters at the plaque erosion site in conservatively treated patients. The results showed that the erosion site had higher values of endothelial shear stress (ESS) and ESS gradient (ESSG), which persisted up to 12 months.
INTERNATIONAL JOURNAL OF CARDIOLOGY
(2022)
Article
Thermodynamics
D. Aljubaili, L. Chan, W. Lu, A. Ooi
Summary: The two-dimensional flow around a confined flat plate was simulated and studied using the spectral element code Nek5000. Four different flow regimes were observed and compared with previous studies on confined circular cylinder flow. Linear stability analysis was also conducted to further confirm the observed flow trends. The effects of the confined wake on hydrodynamic forces of a flat plate were investigated.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2022)
Article
Thermodynamics
Xiaowei Xu, Fabian Waschkowski, Andrew S. H. Ooi, Richard D. Sandberg
Summary: This paper presents robust and accurate Reynolds-averaged stresses and scalar fluxes closure models for natural convection developed using machine learning. A novel multi-objective and multi-expression machine-learning framework based on CFD-driven training is utilized to develop fully coupled buoyancy-extended models, which improves the predictions of natural convection problems by coupling the explicit closure model formulations, choosing appropriate cost functions, and incorporating the correct input flow features.
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
(2022)
Article
Cardiac & Cardiovascular Systems
Vikas Thondapu, Daisuke Shishikura, Jouke Dijkstra, Shuang J. Zhu, Eve Revalor, Patrick W. Serruys, William J. van Gaal, Eric K. W. Poon, Andrew Ooi, Peter Barlis
Summary: Patient-specific coronary endothelial shear stress (ESS) calculations were performed using Newtonian and non-Newtonian rheological models. The non-Newtonian model estimated higher ESS values and offered additional information for detecting underlying atherosclerosis.
FRONTIERS IN CARDIOVASCULAR MEDICINE
(2022)
Article
Thermodynamics
L. Chan, A. Skvortsov, A. Ooi
Summary: Direct numerical simulations were conducted to investigate the flow characteristics over a wall mounted fence confined by two parallel walls at different Reynolds numbers and blockage ratios. The results showed that the length of the primary recirculation bubble varied with Reynolds numbers. A secondary recirculation bubble appeared under certain conditions. The simulation results were consistent with the literature but showed limited agreement with experimental data.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2022)
Article
Biology
Qingdi Wang, Xiaojing Guo, Mark Brooks, Jason Chuen, Eric K. W. Poon, Andrew Ooi, Ruth P. Lim
Summary: MRI provides individualized hemodynamic parameters for Type B aortic dissection (TBAD) in computational fluid dynamics (CFD) studies, enabling personalized treatment and pre-treatment planning. Further research is needed to validate its effectiveness in TBAD surgical planning.
COMPUTERS IN BIOLOGY AND MEDICINE
(2022)
Article
Computer Science, Interdisciplinary Applications
Tony Zahtila, Wilson Lu, Leon Chan, Andrew Ooi
Summary: In this paper, direct numerical simulation of fully developed turbulent channel flow is carried out at low Reynolds number to investigate the effect of grid refinement on turbulence statistics in a spectral element method context. The findings show that discontinuity at shared nodes between adjacent spectral elements creates potential artefacts in the averaged statistical quantities. Grid convergence is fast for spatially-averaged terms, particularly for statistics of primitive variables, but may require additional grid resolution for derivative terms. Statistical convergence with grid refinement occurs more quickly in the near-wall region than in the outer region.
COMPUTERS & FLUIDS
(2023)
Article
Hematology
Nurul A. Zainal Abidin, Mariia Timofeeva, Crispin Szydzik, Farzan Akbaridoust, Chitrarth Lav, Ivan Marusic, Arnan Mitchell, Justin R. Hamilton, Andrew S. H. Ooi, Warwick S. Nesbitt
Summary: Researchers have developed a microfluidic assay to study platelet mechanotransduction in the absence of surface adhesions. They found that platelets are highly sensitive to extensional strain rates and respond to the rate of change in strain. The actin-based cytoskeleton and microtubules play a key role in platelet mechanotransduction under extensional strain.
RESEARCH AND PRACTICE IN THROMBOSIS AND HAEMOSTASIS
(2023)
Article
Engineering, Aerospace
Yuan Fang, Yaomin Zhao, Fabian Waschkowski, Andrew S. H. Ooi, Richard D. Sandberg
Summary: In order to improve the predictive accuracy of data-driven models for a wider range of cases, an extension of a computational fluid dynamics (CFD)-driven training framework is proposed. This framework consists of three key steps, including selecting candidate flow-related parameters, modeling an additional production term, and performing Reynolds-averaged Navier-Stokes (RANS) evaluations on multiple different flows simultaneously during model training iterations. The results show that the machine-learned models from this multicase CFD-driven framework can significantly improve the prediction accuracy for test cases with significant errors from the baseline RANS results.
Article
Thermodynamics
Minghang Li, Shahram Karami, Richard Sandberg, Julio Soria, Andrew Ooi
Summary: This study investigates the physics of impingement heat transfer in under-expanded supersonic impinging jets using wall-resolved large-eddy simulations. It is found that the impinging jets exhibit a strong oscillation of a stand-off shock, resulting in two peaks of the mean heat transfer coefficients.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2023)
Article
Mechanics
Wilson Lu, Daniah Aljubaili, Tony Zahtila, Leon Chan, Andrew Ooi
Summary: In this paper, the flow characteristics of a circular cylinder in a channel with a blockage ratio of 0.7 were investigated using direct numerical simulation. The study revealed a wide range of wake dynamics under different spanwise domain lengths and Reynolds numbers. The presence of top-or bottom-biased asymmetry in the wake was observed at different spanwise locations, which was found to result from the confinement effect. The study also highlighted the dependence of asymmetry on the spanwise domain length and initial conditions, with different numbers of wake flips being observed.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
T. Zahtila, L. Chan, A. Ooi, J. Philip
Summary: In particle-laden turbulent wall flows, the transport of particles towards solid walls is believed to be controlled by the wall-normal turbulence intensity, which supports particle-eddy interactions modeled by turbophoresis and turbulent diffusion. By directly estimating the turbophoretic and turbulent diffusive coefficients from a generated direct numerical simulation (DNS) database, we can predict the particle concentration as a function of wall-normal distance and time. Our results show that the common gradient diffusion hypothesis may be limited for larger particles with higher Stokes numbers (St(+)), as indicated by a favorable comparison with DNS for smaller St(+) particles. Additionally, we explore the effects of St(+), pipe wall condition, drag and lift forces on particle velocity and statistics, and assess Eulerian-based models for turbophoretic and turbulent diffusive coefficients.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Biology
Mariia Timofeeva, Chitrarth Lav, Michael M. H. Cheung, Andrew Ooi
Summary: In this study, the effect of varying conduit stenosis on the hemodynamics in a surrogate TCPC model was investigated using high-fidelity numerical simulations. The results showed that the flow in the TCPC model exhibited pronounced unsteadiness, and the presence of stenosis amplified the chaotic nature of the flow. Furthermore, it was found that respiration added perturbations to the flow, leading to increased power loss.
COMPUTERS IN BIOLOGY AND MEDICINE
(2023)
Article
Thermodynamics
L. Chan, Kevin, A. Skvortsov, A. Ooi
Summary: Direct numerical simulations were conducted to investigate the physical mechanisms involved when inertial effects within straight riblets become important. The parameter assessed was the height to spacing ratio (a = h/s) of the ribs. 'k'-type behavior was observed in all cases, despite the absence of pressure drag component. The presence of closely-packed and large h/s ribs induced Kelvin-Helmholtz (KH) like structures at the tips, leading to large pressure fluctuations, while sparser ribs with low h/s triggered the formation of mean secondary flows that suppressed pressure fluctuations. The drag contribution of these distinct flow features was further analyzed, showing a transitional fully-rough (logarithmic) scaling within the drag-increasing regime.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2023)
Article
Acoustics
S. J. Zhu, A. Ooi, A. Skvortsov, R. Manasseh
Summary: Bubbles can reduce underwater noise propagation through density and acoustic-impedance mismatches, reflection and absorption of sound waves, and bubble-acoustic resonances. A discrete bubble model (DBM) was developed to simulate the noise mitigation effect of bubble curtains. The DBM accurately predicted the resonance frequencies of bubbles in different configurations, and showed that reducing the inter-bubble spacing lowered the collective resonance frequency. Realistic cylindrical bubble curtain configurations with a diameter of 5 m and gas volume fraction values of 1% and 2% were able to reduce broadband acoustic pulse levels by approximately 17 dB. Variations in bubble size significantly impacted curtain performance, while variations in inter-bubble spacing had no significant effect.
JOURNAL OF SOUND AND VIBRATION
(2023)
