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
Mathematics, Applied
Manuel Nunez
Summary: Introducing a magnetic field into the plate generates a perturbation that can be expressed in terms of an Abel transform for lift calculation. Inverting the Abel transform allows for achieving any desired lift distribution on the plate.
ZAMM-ZEITSCHRIFT FUR ANGEWANDTE MATHEMATIK UND MECHANIK
(2022)
Article
Mechanics
Arnab Kumar De, Sandip Sarkar
Summary: The study uses an immersed boundary-based method to compute wake transition behind a pitching panel and observes flow characteristics under different pitching frequencies and aspect ratios. Different vortex structures and wake features appear under different conditions, with observations of certain phenomena but no direct correlation with the growth of secondary instabilities. Thrust and lift signals exhibit different oscillation characteristics under different conditions, with root-mean-squared thrust and lift coefficients increasing with certain factors.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Qingrui Meng, Hongwei An, Liang Cheng, Mehrdad Kimiaei
Summary: Numerical investigation on wake transitions behind an isolated cube revealed four different flow regimes and their evolution patterns. The study also identified the transition mechanisms between vortex shedding states and the critical Reynolds numbers for bifurcations to different regimes.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Chenlin Sun, Azlin Mohd Azmi, Justin Leontini, Hongjun Zhu, Tongming Zhou
Summary: This study investigated the development of large-scale vortex structures in the wake of two screen cylinders with different porosities using X-type hot-wire probes. The results showed that the mechanisms of vortex formation in the wake of screen cylinders with different porosities were different, with one being due to wake instability and the other due to shear-layer convective instability.
Article
Mechanics
Armin Sheidani, Sajad Salavatidezfouli, Giovanni Stabile, Mostafa Barzegar Gerdroodbary, Gianluigi Rozza
Summary: In this study, the effect of icing phenomenon on the wake characteristics of a vertical-axis wind turbine (VAWT) was investigated using high-fidelity computational fluid dynamics simulation. The results showed that icing caused the leading edge vortex and trailing edge vortex to separate faster, resulting in a steeper drop in the power coefficient. The modes of the transversal component of velocity in clean and icy conditions were found to be more similar, while the modes of the streamwise component showed significant differences.
Article
Mechanics
Shijian Wu, Tomas Solano, Kourosh Shoele, Hadi Mohammadigoushki
Summary: In this study, we investigate the effects of helical swimmer shape on swimming dynamics in a constant viscosity viscoelastic fluid. The results show that increasing the swimmer's tail thickness and pitch angle enhances the swimming speed. Furthermore, a front-back flow asymmetry is observed in the viscoelastic flow around the swimmer, and the strength of the negative wake is inversely proportional to the swimming speed. Simulations confirm the formation of a similar front-back flow asymmetry. Finally, the contribution of polymer stresses in the interior region of the helix may provide a mechanism for swimming enhancement or diminution in the viscoelastic fluid.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Physics, Fluids & Plasmas
Biswajit Dutta, Pratikshya Bezbaruah, Nilakshi Das
Summary: The study investigates the diffusion of a three-dimensional dust ensemble in a flowing plasma with a moderate magnetic field using Langevin dynamics simulation. It is discovered that the presence of asymmetric wake potential created by streaming ions can drive the dusty plasma from subdiffusive to superdiffusive regime, revealing a novel wake-dominant regime. The dependence of cross field diffusion coefficient on magnetic field exhibits three distinct behaviors corresponding to different strength of the magnetic field.
PHYSICS OF PLASMAS
(2021)
Article
Mechanics
Jianxun Zhu, Fengjian Jiang, Lars Erik Holmedal
Summary: The study investigates the three-dimensional flow past an elliptic cylinder with an aspect ratio of 0.5 near a moving bottom wall, analyzing the transition between two- and three-dimensional flow regimes for different gap ratios. The flow behavior shows a progression from two-dimensional to three-dimensional with various instabilities and vorticity patterns depending on the gap ratio and Reynolds number.
Article
Mechanics
Fei Wang, Chun-Ho Liu, Jingwei Xie
Summary: This study conducted a large-eddy simulation to investigate turbulent pollutant dispersion in the near wake behind a real, light-duty lorry, with results comparing favorably with simplified vehicle models in the literature. By using proper orthogonal decomposition (POD), flow instabilities in the vertical and horizontal directions, as well as pumping motion, were identified with characteristic frequencies. Additionally, coherence analysis revealed strong modulation behavior and the evolution of the lower vortex system spirally and in-phase near the ground.
Article
Mechanics
Yuan-Heng Zhang, Huan-Feng Duan, Xu-Feng Yan, Alessandro Stocchino
Summary: This paper presents an experimental study on the impact of variable solid volume fractions and aspect ratios on the flow behavior and wake structure of a centre-channel rectangular porous patch. The study establishes the importance of aspect ratio in wake vortex generation. By elongating the patch, a vortex street can be generated due to the promotion of transverse velocity gradient in the wake region. The paper also proposes non-dimensional threshold maps to express the combined effects of solid volume fraction and aspect ratio on the initiation of the wake vortex street.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Physics, Multidisciplinary
Waqas Sarwar Abbasi, Saba Ismail, Sumaira Nadeem, Hamid Rahman, Afraz Hussain Majeed, Ilyas Khan, Abdullah Mohamed
Summary: In this study, the numerical analysis of wake flow control of a single square cylinder by a flat plate is conducted using the lattice Boltzmann method. The study observes three different flow modes depending on the length of the plate. The presence of the plate leads to a reduction in drag and lift coefficients.
FRONTIERS IN PHYSICS
(2023)
Article
Engineering, Aerospace
Uday Narayan Ghosh
Summary: Various plasma models have been developed and shown interesting features in auroral plasma, astro-physics plasmas, and spacecraft observations, based on the acknowledgements of space observations. Soliton theory is efficient in describing nonlinear features, and lump soliton solutions of the Kadomstev-Petviashvili equation have been derived using Viking satellite data. The study of lump solitons is attractive and important due to its wide range of applications, and the structures of lump solitons in auroral magnetized plasma vary with parameters.
ADVANCES IN SPACE RESEARCH
(2023)
Article
Thermodynamics
Suyash Verma, Arman Hemmati
Summary: The wake behavior of an oscillating hydrofoil in combined heaving and pitching motion is numerically evaluated. A dominant elliptic instability feature is observed at 90 degrees phase offset, while a deformed trailing edge vortex evolves at 180 degrees phase offset. No secondary hairpin structures are observed at 225 degrees and 270 degrees phase offset, despite local instability features on the leading edge rollers.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2023)
Article
Mechanics
Suyash Verma, Arman Hemmati
Summary: The study found that an oscillating teardrop hydrofoil with combined heaving and pitching motion generates larger thrust with higher Strouhal numbers, but at the expense of lower propulsive efficiency. The evolution of vortex and the formation and interaction of primary structures are influenced by elliptic instability characteristics.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Physics, Applied
Oguz Han Asnaz, Niklas Kohlmann, Hauke Folger, Franko Greiner, Jan Benedikt
Summary: This study uses a parallel-plate, low-pressure plasma to grow hydrogenated amorphous carbon nanoparticles using an argon-acetylene gas mixture. The effects of prolonged treatment with noble gas and reactive gas mixtures on the particles are investigated, and their size and surface morphology are analyzed using scanning electron microscopy. The results indicate that prolonged treatment with argon leads to an increase in particle size and incorporation of oxygen from gas impurities, while the reactive gas mixtures cause etching of the nanoparticle material without exchange reactions between deuterium and hydrogen atoms.
PLASMA PROCESSES AND POLYMERS
(2022)
Review
Astronomy & Astrophysics
Alan G. Wood, Lucilla Alfonsi, Lasse B. N. Clausen, Yaqi Jin, Luca Spogli, Jaroslav Urbar, James T. Rawlings, Ian C. Whittaker, Gareth D. Dorrian, Per Hoeg, Daria Kotova, Claudio Cesaroni, Antonio Cicone, Jan Miedzik, Ewa Gierlach, Paula Kochanska, Pawel Wojtkiewicz, Golnaz Shahtahmassebi, Wojciech J. Miloch
Summary: Swarm is the first ESA constellation mission for Earth Observation, which studies ionospheric plasma using various instruments and provides a reference for scientific challenges in future work.
SPACE SCIENCE REVIEWS
(2022)
Review
Geochemistry & Geophysics
Lucilla Alfonsi, Nicolas Bergeot, Pierre J. Cilliers, Giorgiana De Franceschi, Lisa Baddeley, Emilia Correia, Domenico Di Mauro, Carl-Fredrik Enell, Mark Engebretson, Reza Ghoddousi-Fard, Ingemar Haggstrom, Young-bae Ham, Georg Heygster, Geonhwa Jee, Antti Kero, Michael Kosch, Hyuck-Jin Kwon, Changsup Lee, Stefan Lotz, Liliana Macotela, Maria Federica Marcucci, Wojciech J. Miloch, Y. Jade Morton, Takahiro Naoi, Monia Negusini, Noora Partamies, Boyan H. Petkov, Eric Pottiaux, Paul Prikryl, P. R. Shreedevi, Rikard Slapak, Luca Spogli, Judy Stephenson, Arantxa M. Triana-Gomez, Oleg A. Troshichev, Roeland Van Malderen, James M. Weygand, Shasha Zou
Summary: The Antarctic and Arctic regions provide unique opportunities for investigating the atmosphere system at high latitudes, which is not well understood. The development of observing infrastructure in these regions has provided scientists with new opportunities to advance our knowledge on the polar atmosphere and geospace. Integrated, multi-disciplinary research using long-term observations combined with ad hoc measurement campaigns is crucial for improving our understanding of atmospheric dynamics in the polar regions.
SURVEYS IN GEOPHYSICS
(2022)
Article
Physics, Fluids & Plasmas
Kai Morgan Kjolerbakken, Wojciech J. Miloch, Ketil Roed
Summary: In this study, the formation time of the surrounding sheath of Langmuir probes in an ionospheric plasma was investigated using a kinetic particle-in-cell model. The results showed that theoretical models can be used to estimate the formation time and determine the sampling rate, and the formation time is primarily affected by the plasma density rather than the temperature or bias voltage. Additionally, applying a step function to the probe can be used to characterize ion species composition or estimate ion density.
JOURNAL OF PLASMA PHYSICS
(2023)
Article
Astronomy & Astrophysics
Florine Enengl, Daria Kotova, Yaqi Jin, Lasse B. N. Clausen, Wojciech J. Miloch
Summary: Auroral particle precipitation has a significant impact on ionospheric plasma structuring. Through multi-point measurements, it is found that plasma structuring affects the GNSS signals the most at the edges of auroral forms. Specifically, elevated phase scintillation index values are observed at the poleward edge of the aurora in the ionospheric E-region.
JOURNAL OF SPACE WEATHER AND SPACE CLIMATE
(2023)
Article
Chemistry, Multidisciplinary
Oguz Han Asnaz, Jonas Drewes, Marie Elis, Thomas Strunskus, Franko Greiner, Oleksandr Polonskyi, Franz Faupel, Lorenz Kienle, Alexander Vahl, Jan Benedikt
Summary: A novel combined setup of a Haberland type gas aggregation source and a secondary radio frequency discharge is used to generate, confine, and coat nanoparticles over much longer time scales than traditional in-flight treatment. The process is precisely monitored using localized surface plasmon resonance and Fourier-transform infrared spectroscopy as in situ diagnostics. Surface coating is shown to occur in two phases: first, singular seeds appear on the particle surface which then grow to cover the entire particle surface over 3 to 5 minutes.
NANOSCALE ADVANCES
(2023)
Review
Astronomy & Astrophysics
Theodoros Sarris, Minna Palmroth, Anita Aikio, Stephan Christoph Buchert, James Clemmons, Mark Clilverd, Iannis Dandouras, Eelco Doornbos, Lindsay Victoria Goodwin, Maxime Grandin, Roderick Heelis, Nickolay Ivchenko, Therese Moretto-Jorgensen, Guram Kervalishvili, David Knudsen, Han-Li Liu, Gang Lu, David M. Malaspina, Octav Marghitu, Astrid Maute, Wojciech J. Miloch, Nils Olsen, Robert Pfaff, Claudia Stolle, Elsayed Talaat, Jeffrey Thayer, Stelios Tourgaidis, Pekka T. Verronen, Masatoshi Yamauchi
Summary: The lower thermosphere-ionosphere (LTI) is a critical transition region between Earth's atmosphere and space. However, its complex interactions between neutral and charged constituents remain poorly characterized due to the lack of in situ measurements. The quantification of key processes in the 100-200 km altitude range is essential for improving atmospheric models and space weather prediction capabilities.
FRONTIERS IN ASTRONOMY AND SPACE SCIENCES
(2023)
Article
Physics, Multidisciplinary
Julia Kobus, Andreas Petersen, Florian Kirchschlager, Nils Rehbehn, Franko Greiner, Sebastian Wolf
Summary: Imaging Mie polarimetry is crucial for determining spatially resolved information about particle cloud properties in reactive particle producing plasmas. The anisotropic scattering of polarized laser light creates asymmetries in the intensity maps, necessitating the use of radiative transfer simulations for analysis. By using RT simulations, we investigate the asymmetric scattering behavior in a model of a typical reactive plasma and explore the potential for analyzing particle properties. We find that the intensity distribution's asymmetry pattern is highly dependent on the refractive index, offering the possibility of determining the refractive index and grain size during the growth process.
NEW JOURNAL OF PHYSICS
(2023)
Article
Astronomy & Astrophysics
P. Sado, L. B. N. Clausen, W. J. Miloch, H. Nickisch
Summary: We classified sky images from four seasons, transformed the results into time-series data, and combined them with information on geomagnetic substorms. We trained a lightweight classifier on this dataset to predict substorm onset within a 15 min interval after being shown aurora information for 30 min. The best classifier achieved a balanced accuracy of 59% with a recall rate of 39% and false positive rate of 20%. We demonstrated that the classifier is limited by a strong imbalance in the dataset, with approximately 50:1 ratio between negative and positive events. All software and results are open source and freely available.
SPACE WEATHER-THE INTERNATIONAL JOURNAL OF RESEARCH AND APPLICATIONS
(2023)
Article
Astronomy & Astrophysics
A. A. Sinevich, A. A. Chernyshov, D. V. Chugunin, L. B. N. Clausen, W. J. Miloch, M. M. Mogilevsky
Summary: This paper examines the internal structuring of Polarization Jet (PJ)/Subauroral Ion Drift (SAID) and identifies the presence of Polarization Jet Strata (PJS) within PJ/SAID. A new phenomenon called Stratified Subauroral Ion Drift (SSAID) is discovered, characterized by small-scale PJS. Measuring the internal small-scale structure of SSAIDs during geomagnetic events using satellite data shows that SSAID consists of 2-4 large PJS and several tens of small PJS, with respective sizes of 0.2-0.3 degrees latitude and < 0.1 degrees.
JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS
(2023)
Article
Physics, Applied
Alexander Schmitz, Andreas Petersen, Franko Greiner
Summary: This study introduces a method using neural networks to analyze the size of nanoparticles in plasma technology and dusty plasmas. Compared to traditional methods, this approach offers higher stability, faster computation, and automation.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2023)
Article
Astronomy & Astrophysics
Yaqi Jin, Wojciech J. J. Miloch, Daria Kotova, Knut Stanley Jacobsen, Dorde Stevanovic, Lasse B. N. Clausen, Nicholas Ssessanga, Federico Da Dalt
Summary: We developed a climatological model for the Arctic ionosphere based on a solar cycle of data from the IGS ROTI maps. By decomposing the ROTI maps using the EOF method, we obtained a model that reflects the drivers of ionospheric irregularities. The model fits well with selected indices, but further improvement is needed during severe storms.
SPACE WEATHER-THE INTERNATIONAL JOURNAL OF RESEARCH AND APPLICATIONS
(2023)
Article
Nanoscience & Nanotechnology
A. Piterskaya, W. J. Miloch, M. Mortensen
Summary: This paper presents a new efficient algorithm based on spectral-Galerkin numerical approximations and a magnetohydrodynamics-Boussinesq model for studying the development of a Rayleigh-Taylor instability. The validity of the algorithm was confirmed through numerical simulations and comparisons with linear stability analysis. The effects of an external magnetic field on the instability were also investigated.
Article
Astronomy & Astrophysics
Yaqi Jin, Joran Idar Moen, Andres Spicher, Jianjun Liu, Lasse B. N. Clausen, Wojciech J. Miloch
Summary: Abrupt changes in solar wind dynamic pressure have a significant impact on the Earth's magnetosphere-ionosphere system. In this study, a flow vortex in the ionosphere was observed during a sudden decrease in solar wind dynamic pressure. The vortex was tracked using radar instruments, and its effects on electron density and temperature were studied.
JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Lisa M. M. Buschmann, John W. W. Bonnell, Scott Bounds, Lasse B. N. Clausen, Craig Kletzing, Sigvald Marholm, Wojciech J. J. Miloch, Roger Roglans, Andres Spicher
Summary: Particle precipitation affects plasma density irregularities in the cusp ionosphere, which can lead to strong scintillations in GNSS signals. Power spectra analysis of electron density measurements from TRICE-2 mission show that there are two regimes of irregularities, dominated by fluid-like processes and kinetic theory, respectively. Additionally, occurrence of double slopes and strong electron density fluctuations are observed during and after precipitation.
JOURNAL OF SPACE WEATHER AND SPACE CLIMATE
(2023)