Article
Mechanics
Zhao-bo Du, Chi-bing Shen, Wei Huang, Bo Fan, Yi Han
Summary: This study numerically evaluates the flow control induced by steady and pulsed micro-jets to reduce shock wave/boundary layer interactions. Results show that using these methods can significantly reduce the volume of the separation zone.
Article
Mechanics
Mengxiao Tang, Yun Wu, Haohua Zong, Shanguang Guo, Hua Liang, Yanhao Luo
Summary: Particle image velocimetry measurement was conducted in a Mach 2.0 supersonic wind tunnel to study shock wave/boundary layer interaction and quantitatively reveal the plasma flow control effect. The results showed a reduction in shock wave drag and decrease in shock wave angle by using a streamwise plasma actuator array as the control device, indicating the effectiveness of the control mechanism. Additionally, the high-frequency actuation was found to play a key role in achieving continuous control.
Article
Engineering, Aerospace
Ziao Wang, Juntao Chang, Chen Kong, Yunfei Li
Summary: Experimental investigation was conducted on micro-ramps for shock train control in a Mach 1.85 supersonic isolator flow, revealing that taller devices generate stronger wake and wave structures for better control. The wake and wave structures eliminate the Mach stem in the shock train leading edge, inhibit boundary layer thickening, slow down supersonic core flow contraction, and promote high total pressure fluid downstream development. The wake structure promotes shock train oscillation and upstream motion, whereas the wave structure restrains oscillation and enhances resistance backpressure downstream.
Article
Mechanics
Pengcheng Quan, Gang Wang, Xiwang Xu, Ke Zhu, Yanguang Yang
Summary: This paper experimentally investigates the effects of herringbone riblets (HRs) on a turbulent boundary layer and shock wave/boundary layer interactions (SWBLIs) at Mach number 3. Three different lengths of HRs strips are applied upstream of the separation zone of SWBLIs on a compression ramp model. Various techniques like high-speed schlieren, oil-flow visualization, and planar laser scattering are used to examine the shock pattern and boundary layer over the model's surface. The experiments provide evidence that HRs make the separation line wavy and reduce the separation zone, and microscale HRs induce large-scale streamwise vortical structures in the boundary layer.
Article
Physics, Fluids & Plasmas
Xingyu Ma, Xuan Gong, Zhanqi Tang, Nan Jiang
Summary: This study experimentally investigates the aerodynamic role of artificial covert feathers on an airfoil and finds that the coverts effectively control flow separation and improve the characteristics of the wake flow area. The coverts also modulate the distribution of turbulent kinetic energy, stabilize the leading-edge and trailing-edge shear layers, and attenuate flow intermittency outside of the wake flow area. These findings are important for understanding the aerodynamic contribution of covert feathers in bird flight and the potential application of bioinspired coverts for flow separation control of aircrafts and unmanned air vehicles.
Article
Mechanics
Luca Galantucci, Michele Sciacca, Nick G. Parker, Andrew W. Baggaley, Carlo F. Barenghi
Summary: This article discusses the leapfrogging of coaxial vortex rings in ultra-cold atomic gases and quantum fluids. Using the two-dimensional point vortex model and solving the Gross-Pitaevskii equation for a Bose-Einstein condensate, it was found that the dynamics of leapfrogging in narrow channels is richer than in unbounded domains, with new regimes identified. The differences between classical and quantum vortex leapfrogging were also discussed, especially when the quantum healing length and compressibility effects become significant.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Thermodynamics
Yue Yang, JuiKui Mao, Pingting Chen, Feilong Wang, Zecan Tu
Summary: This study compares the heat transfer performance of different VGs configurations through numerical simulations, finding that the downstream common-flow-down configuration of VGs can achieve favorable heat transfer enhancement. By increasing the height of VGs and decreasing the spacing between VGs and the jet, the heat transfer efficiency can be further improved.
APPLIED THERMAL ENGINEERING
(2022)
Article
Mechanics
L. Xia, Y. Hua, J. G. Zheng
Summary: The study investigates leading edge flow separation control over a stalled airfoil using a fluidic oscillator, revealing the interaction between oscillating jet and external crossflow leads to the production of spanwise vortices, mitigating flow separation. It is found that a higher mass flow usually leads to a better flow control performance.
Article
Acoustics
Kristian F. Sagmo, Pal-Tore S. Storli
Summary: The experiments compared the effects of three different trailing edge designs on vortex induced vibrations of a hydrofoil. The results showed that the design with vortex generators effectively reduced resonance and maximum strain intensity. The design also weakened the von Karman-type vortex shedding and decreased the correlation of streamwise velocity fluctuations in the wake. The design with serrated trailing edge also reduced velocity fluctuation correlation at lock-off conditions, but the shedding became more coherent and strengthened as the foil vibrations increased towards resonance.
JOURNAL OF SOUND AND VIBRATION
(2023)
Article
Mechanics
Tongbiao Guo, Jian Fang, Ji Zhang, Xinliang Li
Summary: In this paper, the impact of convergent-divergent riblets on a supersonic turbulent boundary layer is examined using direct numerical simulations. The riblets induce spanwise heterogeneity and successfully reduce the area of the separation zone.
Article
Multidisciplinary Sciences
Fatima Abbas, Silke Becker, Bryan W. Jones, Ludovic S. Mure, Satchidananda Panda, Anne Hanneken, Frans Vinberg
Summary: In this study, the researchers used the retina as a model to investigate the process of death and neuronal revival in the central nervous system. They found that under certain conditions, postmortem mouse and human retinas can revive synchronous in vivo-like trans-synaptic transmission. They also identified modifiable factors that drive reversible and irreversible loss of light signalling after death.
Review
Cell Biology
Nicolas Altemose
Summary: This review provides an account of the history and current understanding of HSat1-3, and emphasizes the importance of studying their evolution and roles in health and disease.
SEMINARS IN CELL & DEVELOPMENTAL BIOLOGY
(2022)
Article
Green & Sustainable Science & Technology
Ruifang Jiang, Zhenzhou Zhao, Huiwen Liu, Tongguang Wang, Ming Chen, Junxin Feng, Dingding Wang
Summary: This study simulates and compares the S809 airfoil and Phase VI wind turbine rotating blades based on the gamma-Re-qt transition model. The aerodynamic characteristics and flow field structures of the blade and airfoil are compared under the same Reynolds number to explore the three-dimensional rotation effect on aerodynamic performance. The local angle of attack and relative velocity of the wind turbine blade are obtained using the inverse blade element moment method, and the influence of vortex generators on flow separation is analyzed through torque and pressure coefficients. The results show that the three-dimensional rotation effect is obvious at the blade root and can effectively delay separation, and vortex generators further delay flow separation and increase lift coefficients and output torques of the wind turbine.
Article
Thermodynamics
Cheng-Hung Huang, Li-Wei Liu
Summary: This study investigated the optimal design of a delta winglet vortex generator to improve the heat dissipation performance of a pin-fin heat sink. Experimental results showed that the optimized heat sink with the delta winglet vortex generator had lower bottom temperatures compared to the original design for various inlet air velocities and Reynolds numbers.
CASE STUDIES IN THERMAL ENGINEERING
(2022)
Article
Optics
Sergey A. Ponomarenko
Summary: In this study, it was demonstrated that the presence of a twist phase in a random light beam leads to classical entanglement between phase space degrees of freedom. The bi-orthogonal decomposition of the Wigner function of a twisted Gaussian Schell-model (TGSM) source was found analytically, and the entanglement was quantified by evaluating the Schmidt number of the decomposition. Results showed that classical entanglement of a TGSM source changes with different coherence levels.
Article
Thermodynamics
C. Sanmiguel Vila, R. Vinuesa, S. Discetti, A. Ianiro, P. Schlatter, R. Orlu
EXPERIMENTAL THERMAL AND FLUID SCIENCE
(2020)
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
Thermodynamics
Ahmad Zarei, Sadegh Seddighi, Sohail Elahi, Ramis Orlu
Summary: The study investigates the use of bubble injection to improve cold thermal energy storage in a helical coil heat exchanger, leading to significant improvements in cycle performance, heat transfer rate, and exergy destruction. The effectiveness of bubble injection depends on geometry and flow rate, with an optimal flow rate value observed.
APPLIED THERMAL ENGINEERING
(2022)
Article
Thermodynamics
Xiaobo Zheng, Gabriele Bellani, Lucia Mascotelli, Ramis Orlu, Andrea Ianiro, Carlos Sanmiguel Vila, Stefano Discetti, Jacopo Serpieri, Marco Raiola, Alessandro Talamelli, Ye Li, Nan Jiang
Summary: Hot-wire measurements were conducted in the large-scale pipe-flow facility CICLoPE, showing Re-tau-independent modulation features and geometric characteristics. The study revealed the coherence and phase relations of different scale motions, with AM effects and opposite effects observed in different regions of the pipe flow.
EXPERIMENTAL THERMAL AND FLUID SCIENCE
(2022)
Article
Engineering, Mechanical
Lars H. von Deyn, Marius Schmidt, Ramis Oerlue, Alexander Stroh, Jochen Kriegseis, Benjamin Boehm, Bettina Frohnapfel
Summary: Existing engineering tools can predict the impact of homogeneous surface roughness on near-wall turbulent flows to some extent, but they are not reliable for heterogeneous rough surfaces. In this study, we investigate the effect of ridge-type roughness on turbulent flows inside a combustion engine, and find that it induces large-scale secondary motions. This suggests that large scale secondary motions can also be present in technical flows.
EXPERIMENTS IN FLUIDS
(2022)
Correction
Thermodynamics
Narges Tabatabaei, Ricardo Vinuesa, Ramis Orlu, Philipp Schlatter
FLOW TURBULENCE AND COMBUSTION
(2022)
Article
Thermodynamics
Narges Tabatabaei, Ricardo Vinuesa, Ramis Orlu, Philipp Schlatter
Summary: The study investigates the implementation and performance of tripping techniques in turbulence models. Three alternatives for tripping are assessed, including a recent turbulence generation method, a traditional transition model, and a novel formulation combining the two. Validated with DNS, LES and experimental data, the tripping model shows promising results in a variety of test cases, providing more reliable simulation results by excluding the challenging transition region.
FLOW TURBULENCE AND COMBUSTION
(2022)
Article
Engineering, Mechanical
Davide Gatti, Alexander Stroh, Bettina Frohnapfel, Ramis Oerlue
Summary: This study addresses the question of whether spatial resolution effects should be considered in measurements of turbulent wall-bounded flows over rough surfaces in the fully rough regime. By using a direct numerical simulation database, the researchers find that spatial resolution effects are significant in fully rough flows and can be corrected using an appropriate correction scheme.
EXPERIMENTS IN FLUIDS
(2022)
Article
Mechanics
P. Sujar-Garrido, M. Becerra, R. Orlu
Summary: This paper experimentally and numerically investigates the spatial and time-resolved characteristics of a single surface dielectric barrier discharge (sDBD) actuator, and focuses on its efficiency as a flow-control device. The study finds that the commonly used simplified phenomenological model fails to accurately reproduce the induced wall-jet and underestimates the power consumption. A better phenomenological model or a fully coupled physical plasma model is required to improve the accuracy.
Article
Physics, Fluids & Plasmas
C. Chan, R. Orlu, P. Schlatter, R. C. Chin
Summary: The role of streamwise length scales in turbulent skin friction generation is investigated. It is found that both the motions scaled with local boundary layer thickness and the large-scale ejection and sweep events contribute significantly to turbulent skin friction. The reduction of turbulent skin friction can be achieved by modifying both the large- and small-scale quadrant events.
PHYSICAL REVIEW FLUIDS
(2022)
Article
Engineering, Mechanical
Adalberto Perez, Ramis Orlu, Alessandro Talamelli, Philipp Schlatter
Summary: Flush-mounted cavity hot-wire probes are an alternative to classical hot-wire probes for wall-shear stress measurements, as they avoid the heat transfer issue. However, our study shows that the presence of the cavity changes the nature of the flow field, with an increase in mean velocity and turbulence, and a decrease in shear stress.
EXPERIMENTS IN FLUIDS
(2022)
Article
Engineering, Multidisciplinary
Mohammadreza Manami, Sadegh Seddighi, Ramis Orlu
Summary: Measurement of oil and gas two-phase flow with variable flow regimes can be achieved by studying flow patterns and transitions. This study presents a dynamic neural network method (NARX) for flow rate measurement, which can predict oil and gas flow with variable flow regimes more accurately compared to the multilayer perceptron model (MLP).
Article
Mechanics
Andrea Andreolli, Davide Gatti, Ricardo Vinuesa, Ramis Oerlue, Philipp Schlatter
Summary: The presence of very-large-scale motions in wall-bounded turbulent flows is commonly associated with the superposition of large scales at the wall and the modulation of small-scale near-wall turbulence. This study challenges the current understanding by selectively suppressing either superposition or amplitude modulation and studying the remaining phenomenon. The results indicate that there is still a correlation between the amplitude of small scales near the wall and the large-scale signal in the outer flow even when near-wall large-scale motions are suppressed.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Physics, Fluids & Plasmas
Narges Tabatabaei, Majid Hajipour, Fermin Mallor, Ramis Orlu, Ricardo Vinuesa, Philipp Schlatter
Summary: Wake analysis is crucial for wind-farm planning. Computational fluid dynamics (CFD) is an efficient alternative to expensive and time-consuming wind-tunnel tests. This study compares detailed wind-tunnel experiments with CFD results for wake analysis of a NACA4412 wing section profile. The agreement between CFD, experiments, and the literature is fairly good, indicating that CFD is an adequate methodology for characterizing wings and their wakes.
Article
Physics, Fluids & Plasmas
Narges Tabatabaei, Ramis Orlu, Ricardo Vinuesa, Philipp Schlatter
Summary: The article discusses the issue of wall-interference in wind tunnel tests and proposes the use of inclined sidewalls as a simplified wall insert to reduce this interference. By conducting sensitivity analysis and simulations on a NACA4412 wing at various angles of attack, the study evaluates the impact of wall-interference on aerodynamic forces and local pressure coefficients. The approach of modifying wall-alignment as a calibration parameter shows promising results in reducing wall interference and improving agreement between wind tunnel and free-flight data.
