Article
Mechanics
Alan H. Duong, Thomas C. Corke, Flint O. Thomas
Summary: Experiments using active flow control successfully reduced the viscous drag in turbulent boundary layers and decreased the wall-normal vorticity component, improving turbulence characteristics.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Y. X. Wang, K-S Choi, M. Gaster, C. Atkin, V Borodulin, Y. Kachanov
Summary: This study conducted opposition control of artificially initiated turbulent spots in a low-turbulence wind tunnel in order to delay the transition to turbulence by modifying the turbulent structure within the spots. Through wall-normal jets, the high-speed region of the turbulent spots was cancelled and replaced by a carpet of low-speed fluid. The variable-interval time-averaging technique showed a decrease in burst duration and intensity within the spots, but an increase in burst frequency.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Simon Kneer, Zhengfei Guo, Markus J. Kloker
Summary: This study utilized direct numerical simulations to investigate the effects of various parameters on the laminar-flow-control capabilities of narrowly spaced streaks in a supersonic boundary layer at Mach 2.0. The research found that spectrum-enriching subharmonic modes do not destroy the controlling mechanism, and a complex breakdown scenario triggered by a multi-frequency point source can be effectively controlled.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Physics, Fluids & Plasmas
Yueqiang LI, Bin Wu, Chao Gao, Haibo Zheng, Yushuai Wang, Rihua Yan
Summary: In this study, a spanwise array of bidirectional dielectric barrier discharge (DBD) plasma actuators is used to control the flat-plate turbulent boundary layer at Re ( tau ) = 1140. A novel method of local drag reduction (DR) measurement is proposed based on the features of the DBD plasma control technology and hot-wire anemometer velocity measurements. The control mechanism is inferred to be the combination of meandering streaks into single stabilized streaks.
PLASMA SCIENCE & TECHNOLOGY
(2023)
Article
Engineering, Marine
Qidi Gao, Jinshu Lu, Gaolun Zhang, Jianwei Zhang, Wenfeng Wu, Jiajia Deng
Summary: In this study, the effect of bubble flow on the mechanism of turbulence suppression in bubble drag reduction on a flat plate is experimentally investigated. A specially designed air-injection and flat plate test device is used in a circulating water channel. The PIV system is employed to observe the flow field. The injection position and air flow rate are manipulated to observe the transition of the flow field. It is found that bubble flow can affect the turbulent boundary layer by modifying its thickness and velocity, resulting in the suppression of turbulence. The drag reduction effect is more pronounced when the injection position is located before the transition region. An empirical formula is also established to estimate the skin friction resistance in bubble-flow drag reduction.
Article
Thermodynamics
Jacopo Serpieri, Marc T. Hehner, Jochen Kriegseis
Summary: This study experimentally investigates the possibility of reducing friction drag caused by turbulent flows using wall-mounted plasma actuators. Two large plasma actuator arrays were used in a channel-flow facility, replicating a flow control approach studied in numerical simulations. Flow measurements and characterization of the actuators were performed. The results show an overall increase in flow friction drag, but drag reduction of over 30% was measured at downstream actuation positions.
FLOW TURBULENCE AND COMBUSTION
(2023)
Article
Engineering, Mechanical
Antoine B. Blanchard, Guy Y. Cornejo Maceda, Dewei Fan, Yiqing Li, Yu Zhou, Bernd R. Noack, Themistoklis P. Sapsis
Summary: This study utilizes Bayesian optimization to design open-loop controllers for fluid flows, achieving good performance in both computational and experimental settings. The research demonstrates that Bayesian optimization can identify optimal controllers at a fraction of the cost of other optimization strategies considered in previous studies. Additionally, Bayesian optimization provides a surrogate model for the latent cost function, assisting in painting a complete picture of the control landscape.
ACTA MECHANICA SINICA
(2021)
Article
Mechanics
Xin Wen, Dong Wang, Ziyu Chen, Fan Yang, Chengru Jiang, Yingzheng Liu
Summary: Kirigami structures are used for the first time to achieve dynamic passive flow control by activating and deactivating an array of tilted surface elements on a bluff body. The control performance is validated in a wind tunnel, showing that activated kirigami structures can push the shedding vortices downstream and reduce turbulent intensity and Reynolds shear stress. The performance depends largely on the height and shape of the kirigami structures.
Article
Mechanics
T. Bon, J. Meyers
Summary: Recent studies have shown that surface roughness with dominant spanwise length scales can induce large secondary motions. This study investigates the effect of spanwise heterogeneous surface temperature on closed channel flow through direct numerical simulations. The results demonstrate that secondary flows are excited and influence the mean flow structure, skin friction, and heat transfer. The length scale of the surface temperature heterogeneity strongly affects the outer layer of the flow, while stronger stability reduces the impact of temperature on momentum and heat transfer.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Davide Modesti, Sebastian Endrikat, Nicholas Hutchins, Daniel Chung
Summary: The study conducted direct numerical simulations on the impact of riblets on turbulent flow, revealing the drag change patterns of different riblet geometries and emphasizing the drag increase associated with dispersive stresses carried by secondary flows.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Esther Mateling, Marian Albers, Wolfgang Schroder
Summary: Investigation of the alteration of the near-wall flow field in a turbulent boundary layer flow subjected to spanwise travelling transversal surface waves at a friction Reynolds number Re tau asymptotic to 1525 reveals that this flow control method induces periodic large-scale bursts near the wall and reduces the energetic content of small-scale features. The occurrence of intense large-scale ejections near the wall is crucial for reducing wall-shear stress, as they balance large-scale sweeps from the outer layer, thus attenuating overall fluctuation intensity. Additionally, the periodic secondary flow field interferes with the quasi-streamwise vortices near the wall, deforming their cross-section into an elliptic shape and resulting in vortex disintegration, which, combined with the effect of large-scale ejections, leads to a decrease in wall-normal momentum exchange and the weakening of near-wall streaks.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Paolo Olivucci, Daniel J. Wise, Pierre Ricco
Summary: A study on turbulent channel flow modified by the motion of free rotating discs under the influence of wall turbulence reveals that half discs rotating with finite angular velocity can significantly reduce turbulence activity and skin-friction drag. The maximum drag reduction over the entire walls is 5.6%, and simplified results show excellent agreement with nonlinear results for large disc diameters.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
X. Q. Cheng, C. W. Wong, F. Hussain, W. Schroeder, Y. Zhou
Summary: An experimental study was conducted on controlling a turbulent boundary layer (TBL) on a flat plate using plasma actuators, resulting in a drag reduction of up to 26%. The study found that the drag reduction phenomenon persists downstream, with three distinct spatial regions characterized by drag increase, pronounced drag reduction, and drag recovery, all related to large-scale streamwise vortices.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Engineering, Aerospace
Liyue Wang, Cong Wang, Shuyue Wang, Sheng Qin, Gang Sun, Bo You, Yongjian Zhong
Summary: The application of grooved surface structure is an effective means in turbulence flow control. However, simulating the global flow field directly using massive grids is impractical. This paper proposes a boundary surrogate model to improve computational efficiency by reproducing the effect of the microscopic near-wall region. The results show that the micro/nano grooved surface structure delays the transition from laminar to turbulence, reducing skin friction significantly.
CHINESE JOURNAL OF AERONAUTICS
(2022)
Article
Mechanics
Zhicheng Wang, Dixia Fan, Xiaomo Jiang, Michael S. Triantafyllou, George Em Karniadakis
Summary: This paper demonstrates how to accelerate the computationally taxing process of deep reinforcement learning for active control of bluff body flows at high Reynolds number using transfer learning. The results show that transfer learning greatly reduces training episodes and improves stability compared to training from scratch. The wake flow at high Reynolds number is analyzed, revealing an asymmetry in the hydrodynamic forces on the two rotating control cylinders for the first time.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Thermodynamics
Waleed M. Abed, Richard D. Whalley, David J. C. Dennis, Robert J. Poole
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
(2015)
Article
Mechanics
Waleed M. Abed, Richard D. Whalley, David J. C. Dennis, Robert J. Poole
JOURNAL OF NON-NEWTONIAN FLUID MECHANICS
(2016)
Article
Physics, Applied
Y. Ni, M. J. Lynch, M. Modic, R. D. Whalley, J. L. Walsh
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2016)
Article
Physics, Fluids & Plasmas
Richard D. Whalley, Jae Sung Park, Anubhav Kushwaha, David J. C. Dennis, Michael D. Graham, Robert J. Poole
PHYSICAL REVIEW FLUIDS
(2017)
Article
Engineering, Mechanical
Richard D. Whalley, Kwing-So Choi
EXPERIMENTS IN FLUIDS
(2014)
Article
Mechanics
Richard D. Whalley, Kwing-So Choi
JOURNAL OF FLUID MECHANICS
(2012)
Editorial Material
Mechanics
Richard Whalley, Kwing-So Choi
Review
Engineering, Aerospace
Jin-Jun Wang, Kwing-So Choi, Li-Hao Feng, Timothy N. Jukes, Richard D. Whalley
PROGRESS IN AEROSPACE SCIENCES
(2013)
Article
Multidisciplinary Sciences
Richard D. Whalley, James L. Walsh
SCIENTIFIC REPORTS
(2016)
Article
Engineering, Mechanical
R. D. Whalley, D. J. C. Dennis, M. D. Graham, R. J. Poole
EXPERIMENTS IN FLUIDS
(2019)
Article
Mechanics
R. D. Whalley, W. M. Abed, D. J. C. Dennis, R. J. Poole
THEORETICAL AND APPLIED MECHANICS LETTERS
(2015)
Proceedings Paper
Thermodynamics
Richard D. Whalley, Kwing-So Choi
13TH EUROPEAN TURBULENCE CONFERENCE (ETC13): WALL-BOUNDED FLOWS AND CONTROL OF TURBULENCE
(2011)