Article
Mechanics
Yongliang Yang, Zhe Feng, Mengqi Zhang
Summary: This paper presents the results of numerical simulations and linear stability analyses on the flow past a cylinder. The effects of aspect ratios and Reynolds numbers on vortex shedding are investigated, and a new steady wake pattern is discovered.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Sanjay Mittal, Jawahar Sivabharathy Samuthira Pandi, Mainak Hore
Summary: The study investigates the flow past a cylinder with side walls at various Reynolds numbers and aspect ratios, finding that the complexity of wake transitions increases with aspect ratio. The vortex structures and shedding characteristics change with Reynolds number and aspect ratio, showcasing different flow patterns and shedding modes.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Jawahar Sivabharathy Samuthira Pandi, Sanjay Mittal
Summary: Numerical simulations of flow past a finite rectangular wing with a NACA 0012 section at different semi-aspect ratios and angles of attack have revealed the presence of streamwise vortices. These vortices become stronger and more numerous as the semi-aspect ratio increases and occupy a larger spanwise extent. The local force coefficients show non-monotonic spanwise variation and the strength of the wing-tip vortex increases for higher semi-aspect ratios. Viscous and pressure drag dominate for low and high semi-aspect ratios respectively, and the time-averaged drag coefficient initially decreases and then increases with increasing semi-aspect ratio. Different types of vortex shedding and dislocations are observed for different semi-aspect ratios and angles of attack.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
R. J. Crane, A. R. Popinhak, R. J. Martinuzzi, C. Morton
Summary: This study investigates the wake of a finite wall-mounted circular cylinder, revealing the relationship between periodically shed vortices and the quadrupole structure in the wake. The influence of H/D on the development of the quadrupole is characterized, showing that it emerges as an imprint of shed full-loop structures. The results reconcile mean and instantaneous interpretations satisfying the solenoidal condition on the vorticity field.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Seokbong Chae, Seungcheol Lee, Jooha Kim
Summary: In this study, the effects of rotor-rotor interaction on wake characteristics were experimentally investigated for a twin-rotor configuration in axial descent. The results reveal that the interaction between rotors affects the wake characteristics, especially in the inner region, and the effects vary depending on the descent rate and distance between rotor tips.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Hongyi Jiang, Xiaoyuan Hu, Liang Cheng, Tongming Zhou
Summary: This study examines the turbulent kinetic energy and energy dissipation rate in the wake of a circular cylinder at a Reynolds number of 1000. The results from direct numerical simulation reveal the dominance of the remainder component in the dissipations, highlighting the importance of considering the regions of vortices in the analysis of turbulent wakes. The study also evaluates the validity and performance of different surrogates to the true dissipation rate.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Andrey I. Aleksyuk
Summary: This study investigates energy separation in the wake and the Eckert-Weise effect by numerically solving the Navier-Stokes equations, and examines their sensitivity to flow interference behind side-by-side cylinders. The distance between the cylinders affects the efficiency of energy separation and the intensity of the Eckert-Weise effect.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Chengjiao Ren, Zinan Liu, Liang Cheng, Feifei Tong, Chengwang Xiong
Summary: This study investigates the three-dimensional wake transitions of a steady flow past two side-by-side circular cylinders by using Floquet analysis and direct numerical simulations. The results show that the wake transitions are similar to the isolated cylinder counterpart at large gap-to-diameter ratios (g*), but become complex at small g*. The characteristics formed in the base flows play a significant role in the complexity of the wake transitions.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Xiaoyu Shi, Honglei Bai, Md. Mahbub Alam, Chunning Ji, Hongjun Zhu
Summary: The effects of the spanwise wavelength of a sinusoidal wavy cylinder with an elliptic cross-section on wake structures and fluid forces were investigated numerically. Based on vortical structures, Strouhal number, wake closure length, fluid forces, streamline topologies, and spatio-temporal evolutions, five distinct flow patterns were identified. Pattern III had the minimum drag force and zero fluctuating lift force was observed in patterns III and IV. Flow pattern IV showed alternate vortex shedding over half of the wavelength of the wavy elliptic cylinder, leading to zero fluctuating lift over one complete wavelength. A thorough comparison was made between the wakes of the wavy elliptic cylinder and wavy circular or square cylinders, revealing the underlying flow physics behind the observed behaviors.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Burak Turhan, Zhijin Wang, Ismet Gursul
Summary: This experimental investigation focuses on the flow structure in the near wake of a NACA0012 airfoil undergoing sinusoidal plunging motion. The study reveals the dependence of mean thrust coefficient on Strouhal number and reduced frequency. The analysis suggests that the unsteady characteristics are better correlated with Strouhal number than the mean flow quantities. The study also highlights the importance of Strouhal number in determining the two-dimensionality of the wake.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Yongliang Yang, Chenglei Wang, Rui Guo, Mengqi Zhang
Summary: This work investigates the three-dimensional flow dynamics around a rotating circular cylinder of finite length, and reveals the significant influence of rotation on wake patterns and stability.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Hongyi Jiang
Summary: The study investigates the three-dimensional wake transition for flow past a diamond cylinder at different Reynolds numbers, revealing variations in wake characteristics such as mode swapping between modes A and B, as well as the gradual disorganization of mode B. It is found that there are major differences in wake properties between a diamond and a circular cylinder, with the decomposition of flow properties aiding in the understanding of these differences. The complex interactions between streamwise and spanwise vortices, as well as the wake transition and base-flow transition, are identified as factors that excite mode B and suppress the subharmonic mode.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Anil Pasam, Daniel Tudball Smith, John D. Holmes, David Burton, Mark C. Thompson
Summary: This study investigates the effect of surface roughness on cylinder flows and finds that the roughness Reynolds number can well describe some characteristics of cylinder flow behavior. However, roughness has an impact on the minimum surface pressure coefficient near separation.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Young Dal Jeong, Min Je Kim, Jae Hwa Lee
Summary: Numerical simulations are conducted to explore the intermittent swimming gait of fish schools using two self-propelled flexible fins. Different tail-beating modes, including HT, MTS, and MTL modes, are applied to investigate their effects on lateral gap distances and cost of transport (COT). The results show that MTL mode achieves a stable state with a small lateral gap distance, leading to a smaller COT compared to CT mode.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Remi Bourguet
Summary: The study investigates the effect of a rotating cylinder inclined in a current on flow dynamics, finding that a low inclination angle has limited impact on the global flow evolution, while a high inclination angle leads to a major reorganization of the flow scenario. This includes irregular streamwise structures, pronounced asymmetry, and a significant departure of fluid forces from predictions.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Engineering, Aerospace
David Keisar, Tim De Troyer, David Greenblatt
Article
Engineering, Aerospace
H. F. Mueller-Vahl, C. Strangfeld, C. N. Nayeri, C. O. Paschereit, D. Greenblatt
Article
Mechanics
Lev Dunaevich, David Greenblatt
Article
Engineering, Aerospace
Srimanta Santra, David Greenblatt
Article
Engineering, Aerospace
Yann Delorme, Ronith Stanly, Steven H. Frankel, David Greenblatt
Summary: A hybrid computational approach combining LES and ALM is used to simulate the turbulent wake of a two-bladed rotor in hover. The method is validated against previous predictions and measurements, and demonstrates a novel way to explore active flow control strategies to reduce rotor noise.
AEROSPACE SCIENCE AND TECHNOLOGY
(2021)
Article
Engineering, Mechanical
D. Keisar, B. Eilan, D. Greenblatt
Summary: The study evaluated a novel high pressure vertical axis wind pump for desalination and irrigation. Experimental results showed stable and efficient pressure production, indicating potential for higher efficiency in practical applications. The HP-VAWP system shows promise for various applications in standalone or off-grid environments.
JOURNAL OF FLUIDS ENGINEERING-TRANSACTIONS OF THE ASME
(2021)
Article
Engineering, Aerospace
David Greenblatt, Omer Pfeffermann, David Keisar, Berkant Goeksel
Summary: The use of Dielectric Barrier Discharge (DBD) plasma actuators on Wells turbine impeller blades shows remarkable performance improvements by controlling leading-edge separation. Pulsating perturbations lead to acceleration or deceleration of the impeller, resulting in increased turbine power output compared to plasma power input. The implementation of DBD plasma actuators has the potential to be a game-changing technology, with technical challenges being overcome for successful application.
Article
Energy & Fuels
Alexander Shapiro, Gershon Grossman, David Greenblatt
Summary: One-dimensional unsteady Reynolds-averaged Navier-Stokes computations were conducted for oscillatory transitional and turbulent pipe flows, showing that fully or continuously turbulent models had the best agreement with experimental data when oscillatory Reynolds numbers were substantially higher than 2000, while critically and conditionally turbulent models had slightly inferior correspondence.
Article
Engineering, Aerospace
Dor Polonsky, David Keisar, David Greenblatt
Article
Thermodynamics
A. Garzozi, D. Greenblatt
Summary: The study introduced and investigated a novel concept for wind-driven RO desalination, the CoRe system, which converts wind energy directly to mechanical pumping energy, improving efficiency. Experimental results showed that slot design details play a crucial role in system performance.
Article
Engineering, Aerospace
Tim De Troyer, David Hasin, David Keisar, Srimanta Santra, David Greenblatt
Summary: Experiments on quasi-static and dynamic stall control using plasma actuators on a square-tipped wing with NACA 0015 profile showed different lift improvements under different excitation frequencies, with reduced frequency explaining the differences. Evidence of dynamic stall vortex was absent under dynamic pitching conditions, consistent with prior investigations. Models based on delta-wing concept showed excellent results for both baseline and controlled cases.
Review
Mechanics
David Greenblatt, David R. Williams
Summary: Advancements in unmanned air vehicle technology have led to vehicles with different configurations and sizes. Smaller UAVs rely on vortex generation for lift and maneuvering, while larger UAVs use externally driven and autonomous fluidic systems. Energy efficiency and the development of accurate aerodynamic and flight dynamics models are major challenges.
ANNUAL REVIEW OF FLUID MECHANICS
(2022)
Article
Thermodynamics
Oshri Ifergan, Moshe Berreby, Elaad Mograbi, David Greenblatt
JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER
(2021)
Review
Physics, Fluids & Plasmas
Rene van Hout, Sudharson Murugan, Abhijit Mitra, Beni Cukurel
Summary: This review article focuses on the near-field flow characteristics of coaxial circular jets, discussing the impact of velocity ratios and nozzle geometry on the flow, as well as the presence of shear and wake instabilities. It also explores different states of coaxial jets in the near-field and their potential for specific heat and mass transfer applications.
Proceedings Paper
Green & Sustainable Science & Technology
A. Garzozi, L. Dunaevich, D. Greenblatt
SCIENCE OF MAKING TORQUE FROM WIND (TORQUE 2020), PTS 1-5
(2020)