Article
Engineering, Aerospace
Jun Nyeong Choi, Jae Hwa Lee
Summary: Large-eddy simulations are conducted to investigate the effects of wall-normal steady blowing on the suppression of pressure fluctuations on the cavity walls. When the momentum coefficient (Cμ) is 0.015, a maximum reduction of -7.61% in pressure fluctuations is observed. However, when Cμ>0.05, the pressure fluctuations gradually increase.
AEROSPACE SCIENCE AND TECHNOLOGY
(2023)
Article
Acoustics
Chenghao Yang, Elias J. G. Arcondoulis, Yannian Yang, Jing Guo, Reza Maryami, Chuanxing Bi, Yu Liu
Summary: Large eddy simulation and Ffowcs Williams-Hawkings acoustic analogy were used to investigate the impact of trailing-edge blowing on airfoil self-noise. The aerodynamic and aeroacoustic characteristics of the baseline airfoil were validated and compared. Different blowing ratios and blowing momentum coefficients were considered to assess the noise reduction effects of continuous and local blowing. The results indicated that trailing-edge blowing can achieve a maximum noise reduction of 20 dB, and the underlying mechanisms were analyzed, including the suppression of recirculation bubbles and turbulence fluctuations in the near wake.
JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA
(2023)
Article
Thermodynamics
Li Jiahe, Liu Yanming, Wang Jiang
Summary: A hybrid flow control method using suction and loaded leading edge (SLLE) has been proposed in this study to overcome the huge drag on an airfoil in transonic flow. The passive flow control technique of loaded leading edge structure and the active control of suction slot have achieved significant drag reduction and improved lift-drag ratio.
JOURNAL OF THERMAL SCIENCE
(2023)
Article
Mechanics
Yong Ji, Jie Yao, Fazle Hussain, Xi Chen
Summary: Investigation on vorticity transport in turbulent channels under large-scale active drag control reveals the significant contribution of vorticity fluctuations to frictional drag, with random and coherent components playing different roles in drag reduction. Analysis suggests that suppressing random spanwise-vorticity transport is crucial for more effective drag reduction.
Article
Thermodynamics
H. Mamori, K. Fukudome, K. Tanaka, T. Miyazaki
Summary: This paper investigates the control of skin-friction drag reduction in a fully developed turbulent pipe flow through direct numerical simulations. The heating and cooling of the pipe wall are uniform in the streamwise direction and vary in the azimuthal direction, leading to a decrease in skin-friction drag due to buoyancy force. The study identifies two different mechanisms for skin-friction drag reduction: stable stratification and large-scale vortical structures. The former directly attenuates turbulence through buoyancy force, while the latter creates wall jets and forms large-scale streamwise vortices that increase the coherent contribution to the skin-friction coefficient while indirectly reducing the random contribution.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2023)
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
Azadeh Jafari, Benjamin Cazzolato, Maziar Arjomandi
Summary: This study investigates the potential of finite-length porous surfaces with a subsurface chamber for controlling the turbulent boundary layer. Different chamber configurations were tested, and it was found that a short porous surface with individual cavities underneath each perforation was the most effective in reducing turbulence.
Article
Mechanics
I. C. Chan, R. Orlu, P. Schlatter, R. C. Chin
Summary: A computational study was conducted to investigate skin friction modification by a large-eddy breakup device in a zero-pressure-gradient turbulent boundary layer. Wake vortices generated by the device were observed to propagate downstream towards the wall, leading to skin friction reduction. Skin friction decomposition revealed three universal regions of different changes in skin friction contributions, with the formation and dissipation of wake vortices playing key roles in the reduction process.
Article
Mechanics
S. Parvar, C. B. da Silva, F. T. Pinho
Summary: Direct numerical simulations and large-eddy simulations are used to evaluate the DSIM model for turbulent viscoelastic planar jets. The model shows good performance in inhomogeneous turbulent flows and is able to accurately reproduce flow structures and statistics. The DSIM model is also applicable to other free shear flows of viscoelastic fluids.
Article
Mechanics
Weijie Chen, Xingyu Wang, Yudi Xing, Liangfeng Wang, Weiyang Qiao
Summary: This work presents numerical studies on the effect of wavy leading edges on airfoil instability tonal noise. The results show that the wavy leading edges have a negative impact on the average aerodynamic performance, but significantly reduce lift fluctuations. The instability tonal noise and its harmonic are completely eliminated, but an additional broadband hump appears at the middle frequency. In addition, the wavy airfoil increases low frequency and high frequency noise.
Article
Multidisciplinary Sciences
Ahmed Al-Saadi, Khaled Al-Farhany, Kadhim K. Idan Al-Chlaihawi, Wasim Jamshed, Mohamed R. Eid, El Sayed M. Tag El Din, Zehba Raizah
Summary: This study proposes aerodynamic optimization designs for a sport utility vehicle using computational fluid dynamics analysis. By modifying the vehicle's outer shape and adding aerodynamic devices, the overall aerodynamic behavior can be significantly improved. The optimal design achieves a 12% reduction in drag coefficient and an acceptable lift coefficient.
SCIENTIFIC REPORTS
(2022)
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
Azadeh Jafari, Beverley J. McKeon, Maziar Arjomandi
Summary: The potential of frequency-tuned surfaces as a passive control strategy for reducing drag in wall-bounded turbulent flows is investigated using resolvent analysis. It is shown that wall impedance can suppress the modes resembling the near-wall cycle and the very-large-scale motions and the Reynolds stress contribution of these modes. Furthermore, a wall with only shear-driven impedance is found to suppress turbulent structures over a wider range in spectral space, leading to an overall turbulent drag reduction.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Engineering, Marine
Daiwen Jiang, Hui Zhang, Weiguang Yao, Zijie Zhao, Mingyue Gui, Zhihua Chen
Summary: This paper numerically studies the fully developed turbulent channel flow with sinusoidal deformation controlled by space-dependent electromagnetic forces at Re = 4000. The relationships among characteristic structures in the flow field, mean Reynolds shear stress, and drag reduction are discussed. The results show that quasi-streamwise vortexes generated near the wall can modify the flow structures, suppress mean Reynolds shear stress, and achieve drag reduction. Additionally, the contributions to drag reduction vary at different locations.
Article
Engineering, Marine
Ming-Fu Tang, Guo-Hai Dong, Tiao-Jian Xu, Chun-wei Bi, Sen Wang
Summary: The subcritical flow around cruciform cylinders was analyzed using Large-eddy simulation (LES) technique, investigating the influence of Reynolds number and blockage ratio on the flow pattern and hydrodynamic forces. Different flow patterns were identified for cruciform cylinders under different blockage ratios and their hydrodynamic characteristics were compared.
Article
Thermodynamics
Marian Albers, Pascal S. Meysonnat, Wolfgang Schroeder
FLOW TURBULENCE AND COMBUSTION
(2019)
Article
Physics, Fluids & Plasmas
A. Rubbert, M. Albers, W. Schroeder
PHYSICAL REVIEW FLUIDS
(2019)
Article
Mechanics
Rishabh Ishar, Eurika Kaiser, Marek Morzynski, Daniel Fernex, Richard Semaan, Marian Albers, Pascal S. Meysonnat, Wolfgang Schroeder, Bernd R. Noack
JOURNAL OF FLUID MECHANICS
(2019)
Article
Thermodynamics
Marian Albers, Pascal S. Meysonnat, Daniel Fernex, Richard Semaan, Bernd R. Noack, Wolfgang Schroeder
FLOW TURBULENCE AND COMBUSTION
(2020)
Article
Physics, Fluids & Plasmas
Daniel Fernex, Richard Semaan, Marian Albers, Pascal S. Meysonnat, Wolfgang Schroeder, Bernd R. Noack
PHYSICAL REVIEW FLUIDS
(2020)
Article
Physics, Fluids & Plasmas
Marian Albers, Wolfgang Schroeder
PHYSICAL REVIEW FLUIDS
(2020)
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
Engineering, Multidisciplinary
Gonzalo Brito Gadeschi, Thomas Schilden, Marian Albers, Julian Vorspohl, Matthias Meinke, Wolfgang Schroeder
Summary: Efficient removal of material debris by flushing is crucial for the performance and surface quality in electrical discharge machining (EDM). Particle concentration affects the properties of the particle-dielectricum suspension, influencing heat transfer and manufacturing process. Increasing particle loading has a significant impact on heat transfer and the rate of particle flushing out of the cavity.
ENGINEERING APPLICATIONS OF COMPUTATIONAL FLUID MECHANICS
(2021)
Article
Thermodynamics
Navid Freidoonimehr, Azadeh Jafari, Maziar Arjomandi
Summary: In this study, a high-fidelity flow visualisation technique is used to investigate the resemblance between a turbulent boundary layer generated by different tripping devices in a lab environment and a naturally developed canonical turbulent boundary layer. The study finds that the blockage created by trips is the main factor affecting the turbulence statistics at a certain downstream distance.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2024)
Article
Thermodynamics
Yuning Wang, Alberto Solera-Rico, Carlos Sanmiguel Vila, Ricardo Vinuesa
Summary: This study proposes a method that combines 6-VAEs for modal decomposition and transformer neural networks for temporal-dynamics prediction in the latent space to develop reduced-order models (ROMs) for turbulent flows. The method achieves high reconstruction accuracy and accurate prediction of temporal dynamics.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2024)
Article
Thermodynamics
L. Laguarda, S. Hickel, F. F. J. Schrijer, B. W. van Oudheusden
Summary: Wall-resolved large-eddy simulations were used to investigate the Reynolds number effects in supersonic turbulent boundary layers at Mach 2.0. The study covered a wide range of friction Reynolds numbers and identified trends in various statistics and scaling laws. The size and topology of turbulent structures in the boundary layer were examined, with a focus on the outer-layer motions at high Reynolds numbers. The study also assessed the influence of outer-layer structures on near-wall turbulence and the sensitivity of uniform momentum regions to compressibility.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2024)
Article
Thermodynamics
A. Doehring, T. Kaller, S. J. Schmidt, N. A. Adams
Summary: In this study, well-resolved large-eddy simulations were used to investigate turbulent duct flows with a square cross section. The influence of a modified wall shear stress on the secondary flow was analyzed by artificially modifying the wall shear stress at one of the four walls. The results showed that the modification led to an asymmetrical distribution of the secondary flow source terms, affecting the momentum distribution. Furthermore, the anisotropy of the Reynolds stress tensor, which induces the secondary flow vortices, was significantly affected by the wall shear stress modulation.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2024)