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
Wen-Hua Zhang, Qian-Qian Shao, Yu-Ke Li, Yu Ma, Hong-Na Zhang, Feng-Chen Li
Summary: The study conducted DNS of EIT using the Oldroyd-B model for the first time, revealing the complex energy transformations involved in EIT and confirming the formation of sheet-like structures reflecting polymer extension characteristics.
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
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
Maurizio Quadrio, Alessandro Chiarini, Jacopo Banchetti, Davide Gatti, Antonio Memmolo, Sergio Pirozzoli
Summary: In this study, flow control for reducing turbulent skin-friction drag is applied to a transonic airfoil, resulting in improved aerodynamic performance. The control method involves inducing spanwise forcing on a portion of the suction side of the airfoil. This not only reduces friction locally, but also modifies shock waves, leading to increased lift and decreased drag. The findings suggest that skin-friction drag reduction can be used as a tool to improve the overall aerodynamics of complex flows.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Feng Xie, Jose D. Perez-Munoz, Ning Qin, Pierre Ricco
Summary: A turbulent drag-reduction method utilizing synthetic jet sheets was investigated through direct numerical simulations. By adjusting the angle and height of the jet sheets, a drag reduction of 10% to 30% was achieved. The study also found that the global skin-friction drag reduction was a result of a finite counter flow induced by the interaction between the jet-sheet flow and the main flow.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Mohammad Umair, Sedat Tardu
Summary: Direct numerical simulations were conducted to investigate the drag reduction mechanism in turbulent channel flow with spanwise wall oscillations in the form of streamwise travelling waves (STW). The study revealed that the primary effect of the STW forcing is to attenuate the spanwise turbulent enstrophy at the wall, which is linked to the fluctuating wall shear stress. The suppression of the wall-normal turbulent enstrophy is considered to be subordinate.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
A. Chavarin, G. Gomez-de-Segura, R. Garcia-Mayoral, M. Luhar
Summary: Utilizing the resolvent framework, this study explores the impact of anisotropic permeable substrates on turbulent channel flow, revealing the potential of porous materials to reduce drag in wall-bounded turbulent flows. The findings suggest that substrates with high streamwise permeability and low spanwise permeability can suppress the gain of the corresponding resolvent mode, leading to drag reduction.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Alessio Roccon, Francesco Zonta, Alfredo Soldati
Summary: This study investigates drag reduction in a lubricated channel using direct numerical simulation, revealing a significant reduction in drag under certain conditions dependent on the viscosity ratio of the two fluids. Through detailed energy budget analysis, two distinct drag reduction mechanisms are identified.
JOURNAL OF FLUID MECHANICS
(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
A. Rouhi, M. K. Fu, D. Chandran, A. Zampiron, A. J. Smits, I. Marusic
Summary: Turbulent drag reduction through streamwise travelling waves is investigated over a wide range of Reynolds numbers. Wall-resolved large-eddy simulations are conducted to examine how the frequency and wavenumber of the travelling wave influence the drag reduction. The study finds that the level of turbulence attenuation, and hence drag reduction, changes with the near-wall Stokes layer protrusion height. A range of frequencies is identified where the Stokes layer attenuates turbulence and increases the drag reduction, while outside this range, the strong Stokes shear strain leads to a drop in drag reduction.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Wei Ran, Armin Zare, Mihailo R. Jovanovic
Summary: This paper develops a model-based framework to quantify the effect of streamwise-aligned spanwise-periodic riblets on kinetic energy and skin-friction drag in turbulent channel flow. The study shows that triangular riblets can reliably predict drag-reducing trends, but may lead to performance deterioration for large riblets.
JOURNAL OF FLUID MECHANICS
(2021)
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
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
Mechanics
Suming Wang, Wenhua Zhang, Xinyi Wang, Xiaobin Li, Hongna Zhang, Fengchen Li
Summary: This paper conducts direct numerical simulations of viscoelastic drag-reducing turbulence (DRT) to investigate the essence of its maximum drag reduction (MDR) state. The results show that the MDR state can be both inertial turbulence (IT) and elasto-inertial turbulence (EIT), with the dominant dynamics shifting from IT-related to EIT-related dynamics as the maximum extension length (L) of polymers increases. These findings provide insights for breaking through the MDR limit. Rating: 8/10.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Computer Science, Interdisciplinary Applications
Dilaksan Thillaithevan, Paul Bruce, Matthew Santer
Summary: A novel method for predicting stress within a multiscale lattice optimization framework was proposed and validated through full-scale finite element simulations and stress-constrained optimization problems.
STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION
(2021)
Article
Mechanics
Zahra Soltani, Matthew Santer
INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES
(2020)
Article
Computer Science, Interdisciplinary Applications
Morgan Nightingale, Robert Hewson, Matthew Santer
Summary: This paper introduces a novel methodology for optimizing resonant frequencies in three-dimensional lattice structures using a multiscale approach. Material properties derived from precomputed simulations of the small scale lattice are projected onto response surfaces to describe large-scale metamaterial properties as polynomial functions of the small-scale parameters. Resonant frequencies and mode shapes are obtained through eigenvalue analysis of the large-scale finite element model, with frequency tailoring achieved by imposing constraints on the resonant frequency for compliance minimization optimization. Through a sorting method based on the Modal Assurance Criterion, specific mode shapes can be optimized while reducing the impact of localized modes on the optimization. Three cases of frequency constraints are investigated and compared with an unconstrained optimization to demonstrate the algorithm's applicability, showing that strict frequency constraints can be handled and original ordering of resonant mode shapes can be altered with the use of modal tracking.
STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION
(2021)
Article
Computer Science, Interdisciplinary Applications
Ryan Murphy, Chikwesiri Imediegwu, Robert Hewson, Matthew Santer
Summary: The study presents a robust three-dimensional multiscale structural optimization framework with concurrent coupling between scales, reducing computational expenses and enabling storage of microscale data for support of a greater number of design variables. Additionally, the framework allows for the derivation of structures with functionally graded mechanical properties satisfying various functional objectives.
STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION
(2021)
Article
Mechanics
Sourabh S. Diwan, Jonathan F. Morrison
Summary: The study proposed a three-layer asymptotic structure for turbulent pipe flow, revealing the existence of a Reynolds-number-invariant logarithmic region for the streamwise mean velocity and variance in terms of intermediate variables. The analysis determined the classical von Karman and Townsend-Perry constants from the intermediate-scaled log-law constants.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Engineering, Aerospace
Danielle S. O'Driscoll, Paul J. K. Bruce, Matthew Santer
Summary: A novel rigid deployable aeroshell architecture has been developed, utilizing origami principles to ensure efficient flat stowage during launch and repeatable deployment. By analyzing the dynamic behavior of the optimal design, it was found that panel geometry plays a crucial role in achieving robust, repeatable, and controllable deployment. Experimental testing of a scale model verified the modeled results.
JOURNAL OF SPACECRAFT AND ROCKETS
(2021)
Article
Computer Science, Interdisciplinary Applications
Dilaksan Thillaithevan, Paul Bruce, Matthew Santer
Summary: We demonstrate a methodology for robust optimization using multivariable parameterized lattice microstructures. By introducing material uncertainties at the microscale, we are able to simulate manufacturing variations and design structures tolerant to those variations. We impose different types of material uncertainties to generate more robust structures.
STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION
(2022)
Article
Computer Science, Interdisciplinary Applications
Chikwesiri Imediegwu, Ryan Murphy, Robert Hewson, Matthew Santer
Summary: This paper presents a robust framework for multiscale design of three-dimensional lattices with tailored thermal and thermo-structural characteristics. The approach involves converting discrete evaluations of small-scale lattice unit cell characteristics into response surface models, allowing for continuous functions of lattice micro-parameters. The optimization of individual lattice member dimensions is enabled by the adjoint method and explicit expressions of response surface material property sensitivities, extending previous work focused on linear structural response.
STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION
(2022)
Article
Physics, Fluids & Plasmas
Taihang Zhu, Jonathan F. Morrison
Summary: The turbulent axisymmetric bluff body wake is studied using large eddy simulation, with a focus on the effect of pulsed jet forcing. Spectral proper orthogonal decomposition (SPOD) analysis successfully identifies the dominant modes of the wake flow and the impact of pulsed jet forcing.
PHYSICAL REVIEW FLUIDS
(2021)
Article
Engineering, Manufacturing
Ryan Murphy, Robert Hewson, Matthew Santer
Summary: The study presents the derivation and integration of novel in-loop additive manufacturing constraints for open-walled microstructures within a multiscale optimization framework. By applying these constraints, self-supporting hierarchical structures suitable for additive manufacturing processes are derived, leading to a significant increase in mechanical performance.
ADDITIVE MANUFACTURING
(2021)
Article
Engineering, Aerospace
Pathawee Kunakorn-ong, Zahra Soltani, Matthew Santer
Summary: A design methodology is proposed for deployable tube flexures made of ultra-thin carbon fiber composite, and the cut-out shape is determined using Bayesian optimization technique. The efficiency of the approach is validated through experimentation.
Article
Engineering, Aerospace
Zahra Soltani, Matthew Santer
Summary: We propose a high-fidelity finite element formulation for the analysis of slender thin-walled bodies under highly nonlinear deformation. The formulation uses an independent discretization of the displacement field along the beam axis and over the cross section to capture complex buckling behavior while retaining computational efficiency. The method is applied to the analysis of tape springs, a commonly used component in deployable structures.
Article
Engineering, Aerospace
Tianshu Wang, Matthew Santer
Summary: This paper presents a novel deployable reflector concept based on the origami flasher pattern. The proposed folding architecture achieves rigid foldability for flasher patterns applied to doubly curved surfaces, allowing parabolic reflectors to be divided into a number of rigid panels for efficient stowage. A Bayesian optimization approach is used to find optimal stowage patterns that accommodate finite thickness panels and supporting structures.
JOURNAL OF SPACECRAFT AND ROCKETS
(2023)
Article
Computer Science, Interdisciplinary Applications
Yi-Rong Luo, Robert Hewson, Matthew Santer
Summary: This article describes a design approach that takes into account manufacturing constraints for spatially optimised fibre-reinforced composites. The approach optimises local fibre orientation, fibre volume fraction and density-based topology to determine the optimal design. A continuity equation is used to constrain the fibre orientation and ensure continuous fibres within realistic volume fractions. Fibre paths are reconstructed using two scalar fields to ensure manufacturability, allowing for generation of printer toolpaths. The results demonstrate that this approach successfully guarantees manufacturability with minimal performance loss.
STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION
(2023)
Article
Engineering, Aerospace
T. Zhu, Y. Pan, J. Morrison
Summary: In this study, a compressible large eddy simulation (LES) is performed to investigate the control effect of a pulsed jet actuator on the turbulent wake of an axisymmetric bluff body. The numerical scheme and boundary conditions for the pulsed jet are validated and the results show good agreement with experiments. The analysis reveals that the phase lag of the cavity pressure is determined by the integration of the diaphragm motion and the pulsed jet, and the total pressure loss is concentrated near the slot. Dynamic mode decomposition (DMD) is used to extract coherent structures oscillating at the same frequency as the diaphragm motion, and small-scale high-frequency structures are also observed.
AERONAUTICAL JOURNAL
(2023)