Article
Chemistry, Multidisciplinary
Lorenzo Cacciatori, Carlo Brignoli, Benedetto Mele, Federica Gattere, Celeste Monti, Maurizio Quadrio
Summary: This study assesses for the first time the effects of riblets on the total aerodynamic drag of a low-speed UAV using RANS simulations. The results show that installing riblets with optimal size can significantly reduce the drag coefficient of the aircraft, and installing riblets on the wing can further decrease the drag, improving the cost-benefit ratio.
APPLIED SCIENCES-BASEL
(2022)
Article
Engineering, Chemical
Xiaopei Yang, Jun Wang, Boyan Jiang, Zhi'ang Li, Qianhao Xiao
Summary: This study investigates the effects of sawtooth riblets on NACA4412 airfoil at low Reynolds number, focusing on the impact of riblet length and height on aerodynamic performance. Results show that the most effective riblet length is 0.8 chord, leading to significant improvements in lift and drag coefficients, while the most effective height for a riblet with a length of 0.5 chord is 0.6 mm. Riblets can facilitate a greater improvement in airfoil performance at larger angles of attack.
Article
Engineering, Civil
Vikas Sharma, Sushanta Dutta
Summary: This study aims to improve the aerodynamic performance of navigating objects using bio-inspired surface modification. By investigating the effect of different modified surface structures on drag and flow characteristics, the results show that riblets effectively reduce drag coefficient, decrease energy consumption, and increase navigating speed.
JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS
(2022)
Article
Thermodynamics
Shabnam Raayai-Ardakani
Summary: Periodic and symmetric two-dimensional textures with various cross-sectional profiles are studied to improve the physical response of surfaces. A polynomial framework is proposed to define and measure the profiles of these textures, and their hydrodynamic frictional response is tested. Experimental and numerical results show that textures with concave profiles and height-to-half-spacing ratios of lower and equal to unity offer lower torque compared to smooth surfaces and triangular textures. Polynomials of second order provide sufficient response range without the need for higher order or more complex polynomials.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2022)
Article
Green & Sustainable Science & Technology
Shaotao Fan, Xiangxi Han, Youhong Tang, Yiwen Wang, Xiangshao Kong
Summary: This study proposes a novel biomimetic turbulent drag reduction topology inspired by the special structure of shark skin. The excellent drag reduction performances of the optimized ribletted surfaces are verified by large eddy simulation. The designed riblets exhibit higher turbulent drag reduction behavior and the effects of the riblets on fluid flow behavior and drag reduction mechanisms are discussed.
Article
Thermodynamics
Jiansheng Wang, Jianan Ge, Yuntian Fan, Yuguo Fu, Xueling Liu
Summary: In this paper, the flow behavior in a rectangular channel with miniature riblets (MRs) is investigated numerically. The results show that the MRs effectively reduce drag and improve flow stability, but they also lead to a deterioration in heat transfer performance.
INTERNATIONAL COMMUNICATIONS IN HEAT AND MASS TRANSFER
(2022)
Article
Nanoscience & Nanotechnology
ZiDan Zhou, ShengKun Wang, ZeXiang Yan, DaoYuan Wang, JinJun Deng, Yang He, WeiZheng Yuan
Summary: Riblets inspired by shark skin show great potential in reducing air drag in various industries, with blade riblets currently reaching up to 11% drag reduction. A study introduced multilayer hierarchical riblets (MLHRs) as a method to further improve drag reduction, achieving up to 16.67% reduction in a closed air channel experiment.
ACS APPLIED MATERIALS & INTERFACES
(2021)
Article
Engineering, Aerospace
Monami Sasamori, Seigo Koga, Mitsuru Kurita
Summary: A method for estimating the drag reduction performance of riblets installed on aircraft surfaces was extended to consider the effect of pressure gradient. The study combined wind tunnel test data and computational fluid dynamics analysis to estimate the effectiveness of riblets on arbitrary aircraft surfaces. Results showed that the pressure gradient has a small impact on the overall riblet performance.
JOURNAL OF AIRCRAFT
(2022)
Article
Energy & Fuels
Hoai Thanh Nguyen, Kyoungsik Chang, Sang-Wook Lee, Jaiyoung Ryu, Minjae Kim
Summary: In this study, the effect of parameters on drag-reducing performance of superhydrophobic surfaces was investigated using direct numerical simulation (DNS). The results reveal the drag reduction mechanism through turbulent kinetic energy budget and observation of coherent structures. The study demonstrates that significant drag reduction can be achieved under specific solid fraction and distribution conditions.
Article
Mechanics
Xin-wei Wang, Zi-ye Fan, Zhan-qi Tang, Nan Jiang
Summary: Experimental measurements using TR-PIV were conducted for turbulent boundary layer over smooth, superhydrophobic, and superhydrophobic-riblets surfaces. A drag reduction of about 22.1% was achieved on the superhydrophobic-riblets surface compared to 18.7% on the superhydrophobic surface. Large-scale structures over different surfaces were analyzed to show that the hairpin packets on the superhydrophobic-riblets surface were smaller and weaker than those on the smooth surface, but surpassed them in scale and strength in certain regions.
JOURNAL OF HYDRODYNAMICS
(2021)
Article
Engineering, Multidisciplinary
Vikas Sharma, Sushanta Dutta
Summary: This study is inspired by the denticles found on shark skin, and demonstrates the improvement in aerodynamic characteristics by using similar structures on aerofoils. The results show that riblet structures enhance momentum flux, improve mixing, reduce wake zones, and decrease vorticity and Reynolds stress, leading to drag reduction. These findings suggest the potential of using ribbed aerofoils and encourage further research.
SADHANA-ACADEMY PROCEEDINGS IN ENGINEERING SCIENCES
(2023)
Article
Engineering, Mechanical
Vikas Sharma, Sushanta Dutta
Summary: Flow alteration using the bio-inspired riblet structure is a fascinating field of study resulting in drag benefits. Riblets have no power requirement being a passive method. This work aims to study the effect of riblets on flow and drag behavior using both experimental and numerical analysis.
JOURNAL OF FLUIDS ENGINEERING-TRANSACTIONS OF THE ASME
(2023)
Article
Thermodynamics
S. Endrikat, D. Modesti, M. MacDonald, R. Garcia-Mayoral, N. Hutchins, D. Chung
Summary: The study investigates the breakdown of drag-reduction mechanisms in riblets as their viscous-scaled size becomes large enough for turbulence to approach the wall. Using the minimal-span channel concept, cost-efficient direct numerical simulation of rough-wall flows was conducted to study the inertial-flow mechanisms. Different shapes and sizes of riblets were examined, with findings indicating varying influences on the Kelvin-Helmholtz instability.
FLOW TURBULENCE AND COMBUSTION
(2021)
Article
Engineering, Multidisciplinary
Benjamin W. Hamilton, O. Remus Tutunea-Fatan, Evgueni V. Bordatchev
Summary: The natural surfaces of plants and animals can serve as inspiration for developing fouling-resistant surfaces. This study focused on investigating the mechanism behind drag reduction for underwater surfaces and found that a fish-scale-inspired microstructure exhibited a similar effect. The primary mechanism is a delayed transition to turbulence.
Article
Mechanics
Tongtong Tao, Zhaochang Wang, Jiawei Ji, Yuhang Guo, Yongqing Zhu, Xidong Hu, Kun Liu, Yunlong Jiao
Summary: In this study, a deflecting air cavity generation strategy utilizing superhydrophobic area occupancy and impact angle control is reported. The influence of these factors on water entry dynamics and drag reduction characteristics of spheres is investigated through experimental and theoretical analysis. The results show that the deflection displacement of a hemispherically coated sphere reaches its maximum when the impact angle is 90 degrees. The SHB region-modulated sphere exhibits different air cavity morphologies and achieves faster movement with reduced drag.
Article
Engineering, Aerospace
Simone Di Giorgio, Domenico Quagliarella, Giuseppe Pezzella, Sergio Pirozzoli
AEROSPACE SCIENCE AND TECHNOLOGY
(2019)
Article
Computer Science, Interdisciplinary Applications
Sergio Pirozzoli, Simone Di Giorgio, Alessandro Lafrati
COMPUTERS & FLUIDS
(2019)
Article
Mechanics
Simone Di Giorgio, Sergio Pirozzoli, Alessandro Iafrati
Summary: The breaking of free-surface waves in a periodic domain is numerically simulated using a gas-liquid Navier-Stokes solver. The solver incorporates novel schemes for interface tracking and utilizes a low numerical dissipation scheme to conserve energy in the discrete form. Both two-dimensional and three-dimensional simulations are performed, and the analysis focuses on energy dissipation, air entrainment, bubble fragmentation, statistics, and distribution. The study identifies coherent vortical structures and highlights the correlation between vortical structures and energy dissipation, demonstrating their close relationship in both the mixing zone and the pure water domain.
JOURNAL OF FLUID MECHANICS
(2022)
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)